School of Aerospace, Mechanical and Mechatronic Engineering

Light Field Based 6DoF Tracking of Previously Unobserved Objects

2026-04-28T03:07:53Z

Light Field Based 6DoF Tracking of Previously Unobserved Objects Goncharov, Nikolai; Gray, James Lyndon; Dansereau, Donald Gilbert Object tracking is an important step in robotics and autonomous driving pipelines, which has to generalize to previously unseen and complex objects. Existing high-performing methods often rely on pre-captured object views to build explicit reference models, which restricts them to a fixed set of known objects. However, such reference models can struggle with visually complex appearance, reducing the quality of tracking. In this work, we introduce an object tracking method based on light field images that does not depend on a pre-trained model, while being robust to complex visual behavior, such as reflections. We extract semantic and geometric features from light field inputs using vision foundation models and convert them into view-dependent Gaussian splats. These splats serve as a unified object representation supporting differentiable rendering and pose optimization. We further introduce a light field object tracking dataset containing challenging reflective objects with precise ground truth poses. Experiments demonstrate that our method is competitive with state-of-the-art model-based trackers in these difficult cases, paving the way toward universal object tracking in robotic systems. Each sequence contains the following directory structure: ├── camera_matrix.txt ├── camera_poses ├── depth ├── depth_video.gif ├── gdino_prompt.txt ├── LF_0000 ... ├── LF_XXXX ├── metadata.json ├── object_poses └── video.gif Each frame in the sequence has its own folder and the light field sub-aperture views are contained within. The depth maps are contained within the depth folder. The camera and object poses are contained within the camera_poses and object_poses directories respectively.

Understandings of empathy held by Australian engineering leadership

2026-04-28T03:21:14Z

Understandings of empathy held by Australian engineering leadership Scott-Curwood, Cole Empathy is emerging as a vital engineering skill in light of the growing complexity of engineering work and necessity of human-centred solutions. While there is emerging research on empathy in engineering, there is a lack of specific focus on Australian leaders in this field. Considering the criticality of this demographic to realising systemic change in engineering organisations and the profession, this thesis examines how Australian engineering leaders understand empathy. To achieve this, thematic analysis of semi-structured interviews with seven Australian engineering leaders has been conducted. From this, it is clear that a collective uplift in empathetic skills within engineering is essential, particularly for engineering leaders. However, this necessity varies depending on an individual engineer’s work, which reflects their personal abilities, and is completely natural and acceptable. It is inherently empathetic to recognise and champion the diversity of skills in engineering. Developing empathy as an engineering skill requires holistic and nuanced integration into engineering education as well as whole-of-career development. Self-selecting engineers should be empowered to deepen their empathy skills and a baseline awareness requirement should be established for all graduates. These findings are significant as they challenge the all-or-nothing approach to people skills in engineering while reinforcing their criticality to the future of the profession. This thesis recommends that systemic change should be reflected through a tiered approach to empathy in Engineers Australia’s competency standards involving a Stage 1 awareness and a Stage 2 knowledge. This approach sidesteps the issue of congested undergraduate education programs to deliver a collective uplift in empathetic capability. Ultimately, this thesis provides rich insights from Australian engineering leaders in how empathy might be better integrated into engineering education and the profession.

Event-based Satellite Docking

2026-04-28T03:07:53Z

Event-based Satellite Docking Le Gentil, Cedric; Naylor, Jack; Munasinghe, Nuwan; Mehami, Jasprabhijit; Dai, Benny; Asavkin, Mikhail; Dansereau, Donald G.; Vidal-Calleja, Teresa Dataset to accompany Le Gentil et al. "Mixing Data-driven and Geometric Models for Satellite Docking Port State Estimation using an RGB or Event Camera", IEEE International Conference on Robotics and Automation (ICRA) 2025. In-orbit automated servicing is a promising path towards lowering the cost of satellite operations and reducing the amount of orbital debris. For this purpose, we present a pipeline for automated satellite docking port detection and state estimation using monocular vision data from standard RGB sensing or an event camera. Rather than taking snapshots of the environment, an event camera has independent pixels that asynchronously respond to light changes, offering advantages such as high dynamic range, low power consumption and latency, etc. This work focuses on satellite-agnostic operations (only a geometric knowledge of the actual port is required) using the recently released Lockheed Martin Mission Augmentation Port (LM-MAP) as the target. By leveraging shallow data-driven techniques to preprocess the incoming data to highlight the LM-MAP's reflective navigational aids and then using basic geometric models for state estimation, we present a lightweight and data-efficient pipeline that can be used independently with either RGB or event cameras. We demonstrate the soundness of the pipeline and perform a quantitative comparison of the two modalities based on data collected with a photometrically accurate test bench that includes a robotic arm to simulate the target satellite's uncontrolled motion.

The effect of rotation speed and flow rate on evacuation of particles from a spinning dry powder inhaler capsule

2026-04-28T03:07:53Z

The effect of rotation speed and flow rate on evacuation of particles from a spinning dry powder inhaler capsule Azeem, A; Singh, G; Chan, H-K; Yang, R; Cheng, S; Kourmatzis, A This study investigated a capsule’s powder evacuation behaviour when rotating about its minor axis in a cross flow and considering the effects of rotation speed and flow rate on powder emission. The experimental platform, an optically accessible capsule chamber, was designed to uncover the independent effects of these variables by enabling high-speed imaging of the powder evacuation. The capsules were rotated at three speeds (1500, 2500 and 3650 RPM) and two constant flow rates, 30 SLPM and 60 SLPM (inlet velocity: 16.67 m/s and 33.33 m/s, respectively). Two powders were selected: a lactose carrier, Respitose (SV010, D50 = 104 μm) and Mannitol (D50 = 7 μm), the latter representing pure active pharmaceutical ingredient formulations that form agglomerates. In addition to imaging, the capsule was weighed before and after each device actuation to quantify powder emission. Increasing the flow rate was found to have the largest impact on the mass emitted from the capsule at all rotation speeds. The emitted mass for all cases was highly variable and influenced by the cohesiveness of the powder and subsequent blockage of the capsule aperture. The potential for blockage was more pronounced for mannitol at the high rotation speeds. Emitted dose over time was modelled using a natural logarithm function to describe the rate of emptying and demonstrate the advantage of increased flow rate and favourability of low/- moderate rotation speeds. The study of powder size distribution during evacuation found no significant difference between flow conditions for mannitol, as dispersion was dominated by shearing at the capsule aperture.

SydneyScapes: Image Segmentation for Australian Environments

2026-04-28T03:07:53Z

SydneyScapes: Image Segmentation for Australian Environments Berrio Perez, Julie Stephany; Shan, Mao; Worrall, Stewart; Lyu, Hongyu Autonomous Vehicles (AVs) are being partially deployed and tested across various global locations, including China, the USA, Germany, France, Japan, Korea, and the UK, but with limited demonstrations in Australia. The integration of machine learning (ML) into AV perception systems underscores the need for locally labeled datasets to develop and test algorithms in specific environments. To address this, we introduce SydneyScapes—a dataset tailored for computer vision tasks of image semantic, instance, and panoptic segmentation. This dataset, collected from Sydney and surrounding cities in New South Wales (NSW), Australia, consists of 756 images with high-quality pixel-level annotations. It is designed to assist AV industry and researchers by providing annotated data and tools for algorithm development, testing, and deployment in the Australian context. Additionally, we offer benchmarking results using state-of-the-art algorithms to establish reference points for future research and development.

Neural Network Modelling of Track Profile in Cold Spray Additive Manufacturing

2026-04-28T03:07:51Z

Neural Network Modelling of Track Profile in Cold Spray Additive Manufacturing Ikeuchi, Daiki; Vargas-Uscategui, Alejandro; Wu, Xiaofeng; King, Peter C. Cold spray additive manufacturing is an emerging technology that offers the ability to deposit oxygen-sensitive materials and to manufacture large components in the solid state. For further development of the technology, the geometric control of cold sprayed components is fundamental but not yet fully matured. This study presents a neural network predictive modelling of a single-track profile in cold spray additive manufacturing to address the problem. In contrast to previous studies focusing only on key geometric feature predictions, the neural network model was employed to demonstrate its capability of predicting complete track profiles at both normal and off-normal spray angles, resulting in a mean absolute error of 8.3%. We also compared the track profile modelling results against the previously proposed Gaussian model and showed that the neural network model provided comparable predictive accuracy, even outperforming in the predictions at cold spray profile edges. The results indicate that a neural network modelling approach is well suited to cold spray profile prediction and may be used to improve geometric control during additive manufacturing with an appropriate process planning algorithm.

Cr-Mo-V-W: A new refractory and transition metal high-entropy alloy system

2026-04-28T02:43:41Z

Cr-Mo-V-W: A new refractory and transition metal high-entropy alloy system Ikeuchi, Daiki; D.J.M., King; K.J., Laws; A.J., Knowles; R.D., Aughterson; G.R., Lumpkin; E.G., Obbard Cr-Mo-V-W high-entropy alloy (HEA) is studied, with 2553 K equilibrium solidus and high Cr content to promote protective oxide scale formation, suggesting potential applications in hot, oxidising environments. Alloy Search and Predict (ASAP) and phase diagram calculations found a single phase, body-centred cubic (BCC) solid solution at elevated temperatures, across the range of compositions present within the system - uncommon for a HEA of refractory and transition metals. Density functional theory identified solubility of 22 at.% Cr at solidus temperature, with composition-dependent drive for segregation during cooling. An as-cast, BCC single-phase with the composition 31.3Cr-23.6Mo-26.4 V-18.7 W exhibiting dendritic microsegregation was verified.

Data-Driven Overlapping-Track Profile Modeling in Cold Spray Additive Manufacturing

2026-04-28T03:07:53Z

Data-Driven Overlapping-Track Profile Modeling in Cold Spray Additive Manufacturing Ikeuchi, Daiki; Vargas-Uscategui, Alejandro; Wu, Xiaofeng; King, Peter C. Cold spray additive manufacturing is an emerging solid-state deposition process that enables large-scale components to be manufactured at high-production rates. Control over geometry is important for reducing the development and growth of defects during the 3D build process and improving the final dimensional accuracy and quality of components. To this end, a machine learning approach has recently gained interest in modeling additively manufactured geometry; however, such a data-driven modeling framework lacks the explicit consideration of a depositing surface and domain knowledge in cold spray additive manufacturing. Therefore, this study presents surface-aware data-driven modeling of an overlapping-track profile using a Gaussian Process Regression model. The proposed Gaussian Process modeling framework explicitly incorporated two relevant geometric features (i.e., surface type and polar length from the nozzle exit to the surface) and a widely adopted Gaussian superposing model as prior domain knowledge in the form of an explicit mean function. It was shown that the proposed model could provide better predictive performance than the Gaussian superposing model alone and the purely data-driven Gaussian Process model, providing consistent overlapping-track profile predictions at all overlapping ratios. By combining accurate prediction of track geometry with toolpath planning, it is anticipated that improved geometric control and product quality can be achieved in cold spray additive manufacturing.

Design and Simulation of a Flexible Bending Actuator for Solar Sail Attitude Control

2026-04-28T03:07:52Z

Design and Simulation of a Flexible Bending Actuator for Solar Sail Attitude Control Liu, Meilin; Wang, Zihao; Ikeuchi, Daiki; Fu, Junyu; Wu, Xiaofeng This paper presents the design of a flexible bending actuator using shape memory alloy (SMA) and its integration in attitude control for solar sailing. The SMA actuator has advantages in its power-to-weight ratio and light weight. The bending mechanism and models of the actuator were designed and developed. A neural network based adaptive controller was implemented to control the non-linear nature of the SMA actuator. The actuator control modules were integrated into the solar sail attitude model with a quaternion PD controller that formed a cascade control. The feasibility and performance of the proposed actuator for attitude control were investigated and evaluated, showing that the actuator could generate 1.5 × 10−3 Nm torque which maneuvered a 1600 m2 CubeSat based solar sail by 45° in 14 h. The results demonstrate that the proposed SMA bending actuator can be effectively integrated in attitude control for solar sailing under moderate external disturbances using an appropriate controller design, indicating the potential of a lighter solar sail for future missions.

Data-Efficient Neural Network for Track Profile Modelling in Cold Spray Additive Manufacturing

2026-04-28T03:07:52Z

Data-Efficient Neural Network for Track Profile Modelling in Cold Spray Additive Manufacturing Ikeuchi, Daiki; Vargas-Uscategui, Alejandro; Wu, Xiaofeng; King, Peter C. Abstract: Cold spray is emerging as an additive manufacturing technique, particularly advantageous when high production rate and large build sizes are in demand. To further accelerate technology’s industrial maturity, the problem of geometric control must be improved, and a neural network model has emerged to predict additively manufactured geometry. However, limited data on the effect of deposition conditions on geometry growth is often problematic. Therefore, this study presents data-efficient neural network modelling of a single-track profile in cold spray additive manufacturing. Two modelling techniques harnessing prior knowledge or existing model were proposed, and both were found to be effective in achieving the data-efficient development of a neural network model. We also showed that the proposed data-efficient neural network model provided better predictive performance than the previously proposed Gaussian function model and purely data-driven neural network. The results indicate that a neural network model can outperform a widely used mathematical model with data-efficient modelling techniques and be better suited to improving geometric control in cold spray additive manufacturing.

Characterising entrainment in fountains and negatively buoyant jets

2026-04-28T03:07:53Z

Characterising entrainment in fountains and negatively buoyant jets Milton-Mcgurk, Liam; Williamson, Nicholas; Armfield, Steven; Kirckpatrick, Michael Turbulent fountain flow consists of two distinct stages, the initial ‘negatively buoyant jet’ (NBJ) stage, and the fully developed ‘fountain’ stage. The present study investigates both stages of the flow using particle image velocimetry and planar laser-induced fluorescence, over a range of source Froude numbers, 10≲Fro≲30 , and Reynolds numbers, 5500≲Reo≲7700 . While the velocity and buoyancy profiles in NBJs take similar Gaussian shapes over a wide range of axial locations, this was not observed in fountains. The changing profile shape is most evident in the outer flow (OF) region, while there is a degree of similarity in the inner flow (IF). Entrainment between IF and OF is shown to depend on the local Richardson number, Ri . The fountains are found to have a negative entrainment coefficient, α<0 , for the majority of their height, implying a net radial outflow of fluid from the IF to the OF. An alternative description of entrainment is considered, the ‘decomposed top-hat’ model, where the radial flow is separated into inflow and outflow components that are then estimated using the present experimental data. The inflow component was found to be proportional to the axial IF velocity, which is similar to the classical description of entrainment in pure jets/plumes, while the outflow depends on the local Ri . Entrainment in NBJs may also be described by this framework, which, despite not having an OF, is still subject to an Ri -dependent radial outflow.

Entrainment and structure of negatively buoyant jets

2026-04-28T03:07:53Z

Entrainment and structure of negatively buoyant jets Milton-Mcgurk, Liam; Williamson, Nicholas; Armfield, Steven; Kirkpatrick, Michael; Talluru, Krishna Turbulent negatively buoyant jets occur when the buoyancy of a jet directly opposes its momentum, and will decelerate until its mean momentum is reduced to zero. Here, the flow reverses direction and, for an axisymmetric flow originating from a round inlet, returns annularly towards the source, mixing with the opposing fluid and forming a fountain. This investigation focuses on the initial stage of the flow, before the return flow is established. Data are obtained experimentally using two-dimensional particle image velocimetry and planar laser induced fluorescence for saline/freshwater negatively buoyant jets with source Froude number Fro=30 and Reynolds numbers 5500≲Reo≲5900 at axial locations 18≲z/D≲30 , and compared to a neutral jet. The development of the mean and turbulence profiles with local Fr are investigated, and it is found that, unlike neutral jets and plumes, the turbulence intensity in negatively buoyant jets does not scale with the mean flow. Additionally, the ratio of widths of the buoyancy and velocity profiles, λ , increases along the jet. The entrainment coefficient, α , was estimated for a negatively buoyant jet, and was found to decrease with local Fr , eventually becoming negative, indicating fluid is being ejected from the jet. These observations differ to neutral or buoyant jets and plumes, which approach a constant λ and α in the far field. This different behaviour in negatively buoyant jets is a natural consequence of the strongly decelerating mean flow as a result of opposing buoyancy, which is demonstrated in the context of the integral model framework developed by Morton et al. (Proc. R. Soc. Lond. A, vol. 234, no. 1196, 1956, pp. 1–23).

Effects of respiratory rate on the fluid mechanics of a reconstructed upper airway

2026-04-28T03:07:52Z

Effects of respiratory rate on the fluid mechanics of a reconstructed upper airway Burchell, C; Kourmatzis, A; Zhao, Y; Raco, J; Mekonnen, T; Chan, H-K; Cheng, S This study aims to utilise particle image velocimetry (PIV) techniques to investigate the time-dependant effects of respiratory rate in the extrathoracic airway, to show how they affect the flow field developed. There has been limited validation of computational fluid dynamics (CFD) models using experimental setups. Furthermore, the large majority of existing CFD models focus on rigid airways, not accounting for active deformation through the breathing cycle. Experiments were carried out to expand upon Zhao et al.’s previous study, in which a single respiratory rate was investigated. This studied utilised a transient, sinusoidal flow profile with two respiratory rates of 10 breaths per minute (BPM) and 25 BPM, both achieving a maximum flow rate correlating to 5 L/min in air to simulate tidal breathing. Results from this study showed that respiratory rate had the greatest influence near the onset of the inspiratory and expiratory manoeuvres, with the higher respiratory rate homogenising later in the cycle. It was shown that airway deformation at the level of the soft palate homogenised flow downstream of the deformation which resulted in a lower peak magnitude velocity for approximately 40% of the cycle at the level of the epiglottis, when compared to the rigid airway model.

From laminar to turbulent flow in a dry powder inhaler: the effect of simple design modifications

2026-04-28T03:07:53Z

From laminar to turbulent flow in a dry powder inhaler: the effect of simple design modifications SIngh, G; Tang, P; Cheng, S; Chan, H-K; Kourmatzis, A In order to better understand powder dispersion in dry powder inhaler (DPI) devices, a new powder disperser was designed, which uses flow modifiers to alter powder fluidization behavior so as to physically replicate various flow conditions observed in a range of commercial DPIs. The influence of these modifiers on the performance of the DPI was analyzed for flowrates progressing from laminar (15 L/min) to transitional (30 L/min), and finally turbulent flow regimes (60 L/min) in the device. The aerosol performance of the disperser was measured using a Next Generation Impactor. For flowrate in the laminar regime, powder evacuation from the disperser was generally insufficient (<30%), which was increased to >85% when the device was operated in the turbulent flow regime. In contrast, the highest fine particle fraction (FPF) and lowest throat deposition were achieved when operating in the transitional flow regime. The FPF could be increased further by applying flow modifications such as narrowing the air passage before the powder pocket, inducing localized turbulence (by a grid) near the powder pocket, and by changing the loading position of the powder. Flow modifiers had the most noticeable effect under a laminar flow regime, however, the device operated most efficiently under a transitional flow regime.

Syndromic surveillance of respiratory-tract infections and hand hygiene practice among pilgrims attended Hajj in 2021: A cohort study

2026-04-22T03:34:34Z

Syndromic surveillance of respiratory-tract infections and hand hygiene practice among pilgrims attended Hajj in 2021: A cohort study Mahdi, Hashim A.; Rashid, Harunor; Qashqari, Fadi S.; Hariri, Sumyya H.; Marglani, Osama A.; Barasheed, Osamah; Albutti, Aqel; Alwashmi, Ameen S.; Shaban, Ramon Z.; Booy, Robert; Alfelali, Mohammad Background: This cohort study estimated the incidence of symptomatic respiratory tract infections (RTIs) and hand hygiene compliance with its impact among domestic Hajj pilgrims during the COVID-19 pandemic. Methods: During the week of Hajj rituals in 2021, pilgrims were recruited by phone and asked to complete a baseline questionnaire. Pilgrims were followed up after seven days using a questionnaire about the development of symptoms, and practices of hand hygiene. Syndromic definitions were used to clinically diagnose ‘possible’ influenza-like illnesses (ILI) and COVID-19 infection. Results: A total of 510 pilgrims aged between 18 and 69 (median of 50) years completed the questionnaire, 280 (54.9%) of whom were female, and all of them (except for one) were vaccinated against COVID-19 with at least one dose. The mean (±SD) of pilgrims’ hand hygiene knowledge score (on a scale of 0 to 6) was 4.15 (±1.22), and a higher level of knowledge was correlated with a higher frequency of handwashing using soap and water. Among those 445 pilgrims who completed the follow-up form, 21 (4.7%) developed one or more respiratory symptoms, of which sore throat and cough were the commonest (respectively 76.2% and 42.8%); ‘possible ILI’ and ‘possible COVID-19’ were present in 1.1% and 0.9% of pilgrims. Obesity was found to be a significant factor associated with the risk of developing RTIs (odds ratio = 4.45, 95% confidence interval 1.15–17.13). Conclusion: Hajj pilgrims are still at risk of respiratory infections. Further larger and controlled investigations are needed to assess the efficacy of hand hygiene during Hajj.

Recent advances and applications of polymeric materials in healthcare sector and COVID-19 management

2026-04-22T03:32:50Z

Recent advances and applications of polymeric materials in healthcare sector and COVID-19 management Singh, Rasmeet; Kaur, Jagmehak; Gupta, Kashvi; Singh, Mandeep; Kanaoujiya, Rahul; Kaur, Navneet The coronavirus disease pandemic is considered at its worst and all nations are collectively fighting to improve global public health. In this outlook, polymers and their related materials (including plastics) are the primary sources in the manufacturing of medical and personal protective equipment. Plastics can be mass-produced, economical, and sterilized, which makes them an inevitable material in the medical and healthcare sector. Along with plastics, antibacterial and antiviral coatings, polymeric nanomaterials and nanocomposites, and functional polymers have become excellent materials for COIVD-19. This review centres on the applications of polymer materials in managing the COVID-19 outbreak. Moreover, the utilization of plastics with its healthcare applications are reviewed. Apart from this, major challenges and future directions of these materials have also been discussed. This review will help aspiring researchers to develop the basic understanding of polymeric materials currently employed in medical sector.

Instability Growth and Fragment Formation in air assisted atomization

2026-04-28T03:07:53Z

Instability Growth and Fragment Formation in air assisted atomization Singh, G; Kourmatzis, A; Gutteridge, A; Masri, AR This paper reports an extensive study on the morphology of wave formation on the liquid core of atomizing sprays. The gas velocity, liquid jet velocity, and liquid jet size are varied for two different fuels resulting in a range of liquid jet Reynolds numbers, aerodynamic Weber numbers, and mass flux ratios. The liquid jet-Reynolds number can be used to predict the initiation of jet instabilities, with coaxial air-flow velocity controlling their subsequent growth. A categorization of waves on the surface of the liquid according to their amplitude and wavelength has enabled (i) the identification of a threshold that leads to breakup, and (ii) the isolation of waves that lead to ligament formation from waves that result in droplets. The probability distribution of measured wavelength reasonably matches that of the ligament length, with no requirement for empirical constants. This confirms a direct link between interfacial instabilities and ligament formation in air assisted primary atomization.

Interaction behavior of triple transitional round fountains in a homogeneous fluid

2026-04-28T03:07:53Z

Interaction behavior of triple transitional round fountains in a homogeneous fluid Mahmud, Hasan; Lin, Wenxian; Gao, Wenfeng; Armfield, Steven; He, Yinghe In this study, the PIV and flow visualization techniques and three-dimensional di- rect numerical simulation are used to investigate the behavior of triple transitional round fountains, which are aligned along a straight line, interacting with each other in a homo- geneous fluid over the ranges of 1 ≤ Fr ≤ 10 and 100 ≤ Re ≤ 1000, at a fixed spacing of D/X0 = 6, where Re and F r are the Reynolds and Froude numbers, D is the spacing between the two neighbouring fountain sources, and X0 is the radius of orifices at the fountain source, respectively. The results show that the interaction behavior of triple transitional round fountains, over the ranges of Re and Fr studied, is dominated by the bobbing and flapping motions, and is either steady, or unsteady weakly multi-modal, or unsteady strongly multi-modal. In a steady interaction, the bobbing-flapping motions are only present in its initial development stage and the interaction will attain a steady state in the later stage in which the bobbing-flapping motions are no longer present. In contrast, in an unsteady interaction, the interaction remains unsteady all the time and the bobbing-flapping motions are present at all stages. Among all cases considered, a steady interaction occurs at Re ≤ 300 with Fr = 1 and at Re = 100 with Fr ≤ 5; an unsteady weakly multi-modal interaction occurs at Re = 100 with 6 ≤ F r ≤ 10, at 200 ≤ Re ≤ 300 with 2 ≤ Fr ≤ 10, and at Re = 400 with Fr = 1; and an unsteady strongly multi-modal interaction occurs at 600 ≤ Re ≤ 1000 with Fr = 1 and at 400 ≤ Re ≤ 1000 with2 ≤ F r ≤ 10. Such interaction behavior is found to be similar to that of twin transitional round fountains over comparable ranges of Re and Fr, as discovered by us in an earlier study. It is also found that the two interaction regions formed by the three fountains have essentially symmetrical behavior about the middle fountain for all cases considered. Furthermore, the maximum fountain penetration heights and the maximum thicknesses of the interaction regions of the triple transitional round fountains are quantified with the experimental and numerical results and compared to the available scalings for single fountains at comparable Fr and Re values. Several scaling relations are then developed for these parameters over the ranges of Fr and Re considered.

Characteristics of unsteadiness for transitional plane fountains in linearly stratified fluids

2026-04-28T03:07:53Z

Characteristics of unsteadiness for transitional plane fountains in linearly stratified fluids Inam, Mohammad; Lin, Wenxian; Williamson, Nicholas; Armfield, Steven; He, Yinghe When a fountain is injected into a linearly stratified fluid, its behavior will be governed by the stratification of the ambient fluid, represented by the dimensionless temperature stratification parameter (s), in addition to the Reynolds number (Re) and the Froude number (Fr). In this study, a series of three-dimensional direct numerical simulations (DNS) were carried out using ANSYS Fluent for transitional plane fountains in linearly-stratified fluids with Re, F r and s over the ranges 28 ≤ Re ≤ 300, 3 ≤ F r ≤ 10, and 0.1 ≤ s ≤ 0.5 to study the effects of these governing parameters on the characteristics of such unsteadiness. Empirical correlations to quantify the effects of F r, Re and s over the studied ranges on the characteristics of the unsteadiness are also obtained and compared to the relevant scaling relations developed for weak plane fountains. Keywords: Direct numerical simulation, Plane fountain, Stratification, Transitional flow, Unsteadiness.

Numerical Simulation for Entrainment of Forced Turbulent Fountains

2026-04-28T03:07:53Z

Numerical Simulation for Entrainment of Forced Turbulent Fountains Awin, layth; Armfield, Steven; Williamson, Nicholas; Kirkpatrick, Michael; Lin, Wenxian Numerical simulations are used to investigate the entrainment for forced turbulent fountains over a range of Reynolds numbers, 2000 ≤ Re ≤ 3500, and Froude numbers, 5 ≤ Fr ≤ 24, where Re and Fr are based on the fountain source properties. Other fountain properties such as height and width are also examined to provide information on the general structure of the fountains. The results show that the foun- tains have minimal Reynolds number dependency, while they have a strong linear relation with the Froude number for the cases considered in this study. The entrainment coefficient is obtained as well as scaling constants for height and width in terms of the Froude number.

Transition to asymmetry of transitional round fountains in a linearly stratified fluid

2026-04-28T03:07:52Z

Transition to asymmetry of transitional round fountains in a linearly stratified fluid Gao, Wenfeng; Lin, Wenxian; Liu, Tao; Armfield, Steven; Li, Ming In this study, a series of three-dimensional direct numerical simulations were carried out for transitional round fountains in a linearly-stratified fluid over the ranges of 100 ≤ Re ≤ 400, 1 ≤ F r ≤ 8 and 0.0 ≤ s ≤ 0.3, where F r, Re and s are the Froude, Reynolds, and dimensionless temperature stratification parameters, respectively, to examine, both qualitatively and quanti- tatively, the effect of these parameters on their transition to asymmetry and the asymmetric behavior. It is found that the transition to asymmetry are well represented and quantified by azimuthal velocity, with non-zero or noticeable azimuthal velocity indicating asymmetry. The re- sults show that when F r or Re are small, a fountain remains axisymmetric for all time; however, when Fr or Re are increased to be sufficiently large, the fountain will be axisymmetric initially, before becoming asymmetric and unsteady, ultimately reaching a fully developed quasi-steady stage when each quantity fluctuates over a constant, time-average, value. The stratification is found to play a positive role to stabilize the flow and to reduce or even to eliminate the asymmetric behavior. The numerical results were also used to develop the scaling for the time for transition to asymmetry, which is found to be strongly dependent on Fr and s, while only weakly dependent on Re.

Correlations for maximum penetration heights of transitional plane fountains in linearly stratified fluids

2026-04-28T03:07:52Z

Correlations for maximum penetration heights of transitional plane fountains in linearly stratified fluids Inam, Mohammad; Lin, Wenxian In this study, a series of three-dimensional direct numerical simulations (DNS) were carried out using ANSYS Fluent for transitional plane fountains in linearly stratified fluids with the Reynolds number (Re), Froude number (Fr) and dimensionless temperature stratification parameter (s) over 28 ≤ Re ≤ 300, 3 ≤ Fr ≤ 10, and 0.1 ≤ s ≤ 0.5, to study and quantify the effects of these governing parameters on the maximum fountain penetration height, including the initial one during the early developing stage and the time-averaged one at the quasi-steady state, as well as the time to reach the initial maximum penetration height. The results show that both the initial and time-averaged maximum fountain heights as well as the time to attain the initial maximum fountain height increase with Fr but decrease with s, whereas the effect of Re is negligible, and the fluctuations of the maximum fountain penetration height at some specific locations at the quasi-steady state also follow the similar trends. Empirical correlations to quantify the effects of Fr, s and Re on these bulk fountain behavior parameters were obtained from the DNS results over the ranges of Fr, s and Re considered.

Entrainment in Pulsing Plumes

2026-04-28T03:07:53Z

Entrainment in Pulsing Plumes Huang, Danlan; Williamson, Nicholas; Armfield, Steven Turbulent axisymmetric lazy plumes produced by discharging saline fluid downwards into a less dense uniform environment from a round pipe are exam- ined experimentally. The plumes development is con- trolled by the source flow rate Q0, momentum M0 and buoyancy F0. This study investigated plumes where the flow rate Q0(t), momentum M0(t) and buoyancy F0(t) are sinusoidal functions of time. The pulsing flow is generated by a programmable ISMATEC gear pump. The maximum frequency f of this pulsing plume is of O(U0/D), where D/U0 is the eddy turnover time scale at the source, D is the source diameter, U0 is the average velocity at the source. Experiments with puls- ing plumes were carried out with a flow rate ampli- tude A of up to 80% and with Strouhal number St =fD/U0 ranging from 0.012 to 1.2. The bulk dilution and entrainment measurements were made by using the experimental approach of Hunt and Kaye (2001). Average local entrainment is obtained via the integral relationship for Q(z) and M(z) from the model estab- lished by Morton et al. (1956) for continuous sources. The influence of the amplitude of source flow rate and Strouhal number St on the entrainment coefficient α is examined, found to be very small over the entire range of source conditions considered.

Experimental investigation into turbulent negatively buoyant jets using combined PIV and PLIF measurements

2026-04-28T03:07:53Z

Experimental investigation into turbulent negatively buoyant jets using combined PIV and PLIF measurements Milton-McGurk, Liam; Williamson, Nicholas; Armfield, Steven; Kirkpatrick, Michael Turbulent negatively buoyant jets occur when the buoyancy of a jet opposes its source momentum. In these flows, the fluid will rise until it reaches a stagnation point and a return flow is established, forming a fountain (Hunt and Burridge, 2015). This study looks at both the initial negatively buoyant jet stage of this flow, before the return flow has established, and the fully developed fountain stage. Two-dimensional particle image velocimetry (PIV) and planar laser in- duced fluorescence (PLIF) are used to simultaneously measure the velocity and scalar concentration fields. An experimental and image processing procedure for the PLIF is introduced that accounts for pulse-to-pulse variations in laser power and beam profile for an Nd:YAG laser, which has been demonstrated to reduce the error in scalar concentration measurements. The flow is investigated experimentally using a 1m3 tank of salt-water ambient with freshwater+ethanol negatively buoyant jets, allowing for measurements to be taken at F ro = 30 and Reo = 5900. The entrainment coefficient for a negatively buoyant jet has been estimated as α ∼= 0.054, lower than a neutral jet at α ∼= 0.058. A finding con- sistent with existing literature (Bloomfield and Kerr, 2000; McDougall, 1981).

Turbulence structure of neutral and negatively buoyant jets

2026-04-28T03:07:52Z

Turbulence structure of neutral and negatively buoyant jets Talluru, Krishna; Armfield, Steven; Williamson, Nicholas; Kirkpatrick, Michael; Milton-McGurk, Liam High-fidelity measurements of velocity and concentration are carried out in a neutral jet (NJ) and a negatively buoyant jet (NBJ) by injecting a jet of fresh water vertically downwards into ambient fresh and saline water, respectively. The Reynolds number (Re)based on the pipe inlet diameter (d) and the source velocity (Wo) is approximately 5900 in all the experiments, while the source Froude number based on density difference is approximately 30 in the NBJ experiments. Velocity and concentration measurements are obtained in the region 17 ≤ z/d ≤ 40 (z being the axial coordinate) using particle image velocimetry and planar laser induced fluorescence techniques, respectively. Consistent with the literature on jets, the centreline velocity (Wc) decays as z−1 in the NJ, but in the NBJ, Wc decays faster along z due to the action of negative buoyancy. Nonetheless, the mean velocity (W) and concentration (C) profiles in both the flows exhibit self-similar Gaussian form, when scaled by the local centreline parameters (Wc,Cc) and the jet half-widths (rW , rC ). On the other hand, the turbulence statistics and Reynolds stress in the NBJ do not scale with Wc. The results of autocorrelation functions, integral length scales and two-dimensional correlation maps show the similarity of turbulence structure in the NJ and the NBJ when the axial and radial distances are normalised by the local jet half-width. Further, the spectra and probability density functions are similar on the axis and only minor differences are seen near the jet interface. The above findings are fundamentally consistent with our recent analysis (Milton-McGurk et al., J. Fluid Mech., 2020b), where we observed that the mean and turbulence statistics in the NBJ have different development characteristics. Overall, we find that the turbulence structure of the NBJ (when scaled by local velocity and length scales) is very similar to the momentum-driven NJ, and the differences (e.g. spreading rate, scaling of turbulence intensities, etc.) between the NJ and the NBJ seem to be of secondary importance.

Entrainment and structure of negatively buoyant jets

2026-04-28T03:07:52Z

Entrainment and structure of negatively buoyant jets Milton-McGurk, Liam; Williamson, Nicholas; Armfield, Steven; Kirkpatrick, Michael; Talluru, Krishna Turbulent negatively buoyant jets occur when the buoyancy of a jet directly opposes its momentum, and will decelerate until its mean momentum is reduced to zero. Here the flow reverses direction and, for an axisymmetric flow originating from a round inlet, returns annularly towards the source, mixing with the opposing fluid and forming a fountain. This investigation focuses on the initial stage of the flow, before the return flow is established. Data is obtained experimentally using two-dimensional particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) for saline/freshwater negatively buoyant jets with source Froude number F ro = 30 and Reynolds numbers 5500 􏰁 Reo 􏰁 5900 at axial locations 18 􏰁 z/D 􏰁 30, and compared to a neutral jet. The development of the mean and turbulence profiles with local Fr are investigated, and it is found that, unlike neutral jets and plumes, the turbulence intensity in negatively buoyant jets does not scale with the mean flow. Additionally, the ratio of widths of the buoyancy and velocity profiles, λ, increases along the jet. The entrainment coefficient, α, was estimated for a negatively buoyant jet, and was found to decrease with local Fr, eventually becoming negative, indicating fluid is being ejected from the jet. These observations differ to neutral or buoyant jets and plumes, which approach a constant λ and α in the far field. This different behaviour in negatively buoyant jets is a natural consequence of the strongly decelerating mean flow as a result of opposing buoyancy, which is demonstrated in the context of the integral model framework developed by Morton et al. (1956).

Effect of Inflow Conditioning for Dry Powder Inhalers

2026-04-28T03:07:52Z

Effect of Inflow Conditioning for Dry Powder Inhalers Singh, G; Lowe, A; Azeem, A; Cheng, S; Chan, HK; Walenga, R; Kourmatzis, A The transport of pharmaceutical dry powder inside an optically accessible inhaler-like device is studied using both macro- and microscopic high-speed imaging. The investigation aims to systematically study the effect of inflow modifications on the dispersion characteristics of agglomerates inside a dry powder inhaler (DPI) geometry. An inhaler device was designed with geometrical features akin to commercial inhalers used in the current market and research oriented inhalers such as the Twincer®: two offset inlet channels (one with a powder pocket), a clockwise swirling chamber and a single outlet channel. At the device outlet, a vacuum pump was fitted with an actuator and calibrated to achieve a steady state inhalation with a peak flowrate of 85 and 125 L/min. Airflow conditions at the intake of the device were strategically perturbed in order to induce powder fluidisation and dispersion using turbulence grids and through physically obstructing channel streams in order to achieve changes in flow behaviour (e.g., flow separation). Complete fluidisation of the powder bed was observed with image processing enabling statistics on de-agglomerated fragment size and velocity. A range of behaviour was noted including local turbulence through introduction of a grid, bimodal fragment size behaviour for cohesive mannitol powder, as well as introduction of low velocity zones in the device through flow splitting. The geometry enables simple systematic study of inflow conditions into a DPI-like device with the data being useful for study of a given powder formulation (mannitol) and validation of computational models.

Local dynamics of pharmaceutical powder fluidization using high speed long distance microscopy and particle image velocimetry

2026-04-28T03:07:52Z

Local dynamics of pharmaceutical powder fluidization using high speed long distance microscopy and particle image velocimetry Elserfy, K; Cheng, S; Chan, HK; Kourmatzis, A The local dynamics of fluidized pharmaceutical carrier powders in a turbulent channel flow was studied using particle image velocimetry (PIV) and High-speed, long-distance microscopy (HS-LDM). Four different lactose powders which have been used as a drug carrier in dry powder inhalers were used in this study. These powders have median powder particle diameters ranging between 61 and 121 µm. Air flow velocities ranging between 13.3 m/s and 66.7 m/s were examined. In addition, the effect of grid blockage ratio (ranging from ~25% to ~40% of the area of channel cross-section) was also investigated. Results show that the high-speed, long-distance microscopy (HS-LDM) technique was able to capture the mean velocity of the particles, and the results corresponded well with the PIV measurements. Results from the high-speed, long-distance microscopy (HS-LDM) method also demonstrate that the span of particle velocity closely follows that of the particle size distribution both for cohesive and non-cohesive powders. This study contributes towards an improved understanding of pharmaceutical carrier dynamics in turbulent channel flows and demonstrates how advanced image processing can be used to capture local particle dynamics.

Fragmentation dynamics of single agglomerate-to-wall impaction

2026-04-28T03:07:52Z

Fragmentation dynamics of single agglomerate-to-wall impaction Lowe, A; Singh, G; Chan, HK; Masri, AR; Cheng, S; Kourmatzis, A The de-agglomeration characteristics of single agglomerate-wall impaction are examined using high-resolution shadowgraph imaging. Experiments are performed to investigate the effects of constituent particle size (D50 from 3 to 7 μm) and air velocity on the individual size and velocity of de-agglomerated fragments at conditions relevant to dry powder inhalation systems. De-agglomerated fragment area and trajectories were used to differentiate between pseudo-elastic and inelastic collisions during de-agglomeration. Advanced image processing techniques have enabled provision of joint population distributions of fragment area and aspect ratio, which identify a bimodal dispersion of fragments during de-agglomeration. The bimodality is destroyed with increasing air velocity and also generally diminishes with time after impact. The experiment presented forms a platform for the detailed quantitative characterisation of de-agglomeration behaviour and can be useful towards the development and validation of related computational models for pharmaceutical dry powder inhalers.

Fluidization of lactose carrier powders through normally directed airflow: The effect of recirculation and particle size

2026-04-28T03:07:53Z

Fluidization of lactose carrier powders through normally directed airflow: The effect of recirculation and particle size Elserfy, K; Kourmatzis, A; Singh, G; Chan, HK; Cheng, S This study investigates the fluidization of lactose carriers from a powder bed subjected to a normal force in a channel flow using high-speed imaging, particle image velocimetry (PIV), and high-speed, long-distance microscopy (HS-LDM). Pharmaceutical lactose carriers (LH200 and SV010) with different cohesiveness and fines percentages were examined in this study. Airflow velocities in the range of 1.4 m/s and 7m/s were tested, corresponding to flow rates ranging from 20 to 100 L/min. The use of HS-LDM in tandem with PIV has enabled measurement of the slip factor between particles and conveying airflow as well as metrics that help to identify dose homogeneity as a function of location in the channel flow. The results indicate a lower slip ratio and a larger change in powder particle size bands percentages along with channel height in the region near the powder bed, because of flow recirculation and higher velocity fluctuation observed in that region.

Extending the range of back-lit imaging in two-phase flows using an interrogation window based method

2026-04-28T03:07:52Z

Extending the range of back-lit imaging in two-phase flows using an interrogation window based method Singh, G; Kourmatzis, A; Lowe, A; Masri, AR; Chan, HK; Cheng, S This paper introduces a novel image processing methodology to enable an extension of the range of applicability of the back-lit imaging method to provide the simultaneous measurement of size and velocity in turbulent flows with a high concentration of objects having various shapes and sizes. The new image processing methodology applies an interrogation-window method similar to that used in particle image velocimetry, alongside interface identification as used in backlight imaging. The matching of droplets or particles of arbitrary shape is achieved by dividing the image into several small windows and cross-correlating objects in each window to obtain a coefficient of dissimilarity, extracted using a variety of metrics of droplet or particle morphology. To demonstrate its utility this technique is applied to measurement of velocities from (i) a highly turbulent spray flow and (ii) a swirling particle-laden flow as applicable to dry powder inhalation systems. Results are validated against phase Doppler anemometry data and a sensitivity analysis of the controlling parameters of the image processing methodology demonstrate that the technique is robust for a variety of input conditions. A key advantage of this approach lies in complementing the diagnostics capability of PDA methods to span a broader range of particle sizes irrelevant of shape and particle concentration.

Evolution of thermally stratified turbulent open channel flow after removal of the heat source

2026-04-28T03:07:53Z

Evolution of thermally stratified turbulent open channel flow after removal of the heat source Kirkpatrick, Michael Philip; Williamson, Nicholas; Armfield, Steven William; Zecevic, Vanja Evolution of thermally stratified open channel flow after removal of a volumetric heat source is investigated using direct numerical simulation. The heat source models radiative heating from above and varies with height due to progressive absorption. After removal of the heat source the initial stable stratification breaks down and the channel approaches a fully mixed isothermal state. The initial state consists of three distinct regions: a near-wall region where stratification plays only a minor role, a central region where stratification has a significant effect on flow dynamics and a near-surface region where buoyancy effects dominate. We find that a state of local energetic equilibrium observed in the central region of the channel in the initial state persists until the late stages of the destratification process. In this region local turbulence parameters such as eddy diffusivity kh and flux Richardson number Rf are found to be functions only of the Prandtl number Pr and a mixed parameter Q , which is equal to the ratio of the local buoyancy Reynolds number Reb and the friction Reynolds number Reτ . Close to the top and bottom boundaries turbulence is also affected by Reτ and vertical position z . In the initial heated equilibrium state the laminar surface layer is stabilised by the heat source, which acts as a potential energy sink. Removal of the heat source allows Kelvin–Helmholtz-like shear instabilities to form that lead to a rapid transition to turbulence and significantly enhance the mixing process. The destratifying flow is found to be governed by bulk parameters Reτ , Pr and the friction Richardson number Riτ . The overall destratification rate D is found to be a function of Riτ and Pr .

The influence of sharp meanders on thermally stratified open channel flow

2026-04-28T02:43:43Z

The influence of sharp meanders on thermally stratified open channel flow Nguyen, Duy; Kirkpatrick, Michael Philip In this study, direct numerical simulation (DNS) results for turbulent stratified open channel flow through an idealized meander with an internal heat source that models radiative heating from above are used to investigate the effect of bends on the degree of stratification and the mechanism by which the turbulence kinetic energy is produced and redistributed along the channel centreline. The pronounced local increase of TKE gains strength in the area entering halfway in the bend where a local extremum of TKE is found near the outer bank. The curve is sharp with the ratio of minimum radius of curvature to depth Rmin=B=1:67, the maximum deviation angle of q0 =110 degrees with the ratio of width over depth B/H = 10, the meander wavelength to depth l/H = 11, and the friction Reynolds number Ret = 180. We find that there is an explosion of turbulence at the location of 35% of the distance along the channel centreline which gradually weakens in the downstream part of the bend. Possible causes of this feature are discussed.

Direct numerical simulation and large eddy simulation of wind shear effects on non-stratified open channel flow

2026-04-28T02:43:41Z

Direct numerical simulation and large eddy simulation of wind shear effects on non-stratified open channel flow Lashkarbolouk, Hadi; Kirkpatrick, Michael Philip; Williamson, Nicholas; Armfield, Steven William; Lin, Wenxian In this study, direct numerical simulation (DNS) and large eddy simulation (LES) of turbulent channel flow beneath a flat surface with imposed wind shear stress are presented. An open channel with friction Reynolds number Reτ= 360 has been considered, while wind shear stresses were imposed as being aligned with the flow direction or not aligned with components in streamwise and spanwise directions. The results indicate that there are differences between wind-driven flow and the case with no wind shear stress. Streaks are present close to the surface in wind-driven flow and profiles of the mean velocity, TKE and mean shear production rate in wind-driven flow are different from those in the unsheared surface flow. Large eddy simulation of wind-driven flow was also carried out to evaluate the performance of sub-grid scale models. It is shown that the features of the flow observed in DNS are well simulated by LES with a relatively small difference near the surface due to shear stress boundary condition.

Entrainment across a sheared density interface in a cavity flow

2026-04-28T03:07:53Z

Entrainment across a sheared density interface in a cavity flow Williamson, Nicholas; Kirkpatrick, Michael Philip; Armfield, Steven William The entrainment of fluid across a sheared density interface has been examined experimentally in a purging cavity flow. In this flow, a long straight cavity with sloped entry and exit boundaries is located in the base of a straight open channel. Dense cavity fluid is entrained from the cavity into the turbulent overflow. The cavity geometry has been designed to ensure there is no separation of the overflow in the cavity region, with the goal of avoiding cavity-specific entrainment mechanisms as have been encountered in most previous experiments using similar arrangements. Results are obtained over a bulk Richardson number range Rib=gΔρD/ρ0U2b=1 to 19, where D and Ub are the depth of the mixed layer and bulk velocity in the cavity, respectively. The experiments cover the Reynolds number range Re=UbD/ν=7100 to 15 100 and interface length to mixed layer depth ratios of 2.4 to 16. Particle image velocimetry and laser induced fluorescence measurements indicate the flow regime over this entire range is one dominated by the Holmboe wave instability. The non-dimensional entrainment rate, E=ue/Ub , is shown to scale with the bulk Richardson number. We find that the entrainment scaling E=CRi−1.38b applies over the entire experimental range, with no apparent dependence on interface length. The exponent in the scaling is similar to previous non-cavity-based sheared interface flows, however, the constant C is up to an order of magnitude smaller. Close agreement is, however, obtained by instead correlating entrainment with the local gradient Richardson number centred on the interface, rather than bulk quantities. We obtain E=0.0021Ri−0.63g for data over 10

Convectively unstable turbulent open channel flow with stable surface stratification

2026-04-28T02:43:39Z

Convectively unstable turbulent open channel flow with stable surface stratification Williamson, Nicholas; Kirkpatrick, Michael Philip; Armfield, Steven William; Norris, Stuart We use direct numerical simulations to examine fully developed turbulent open channel flow where the near wall region is unstably stratified and the outer boundary layer is stably stratified. The simulations are a model for flow in shallow turbid river channels with incident solar radiation. The aim is to determine under what conditions and by what mechanism the stably stratified layer is overturned. The flow is attained by applying a radiative heat flux at the free surface of the open channel. The absorption and transmission of the radiation follows the Beer--Lambert law with a constant absorption coefficient. We examine conditions where approximately 20% of the incident radiative heat flux penetrates through to the wall, releasing heat at the wall as a heat flux. The problem is specified by our buoyancy parameter which is analogous to the bulk Obukhov length scale. In the stable outer boundary layer we observe that the flux Richardson number reaches the limiting value, as was observed in the atmospheric boundary layer under sheared convective conditions.

Rectangular lattice Boltzmann method using multiple relaxation time collision operator in two and three dimensions

2026-04-28T03:07:52Z

Rectangular lattice Boltzmann method using multiple relaxation time collision operator in two and three dimensions Zecevic, Vanja; Kirkpatrick, Michael Philip; Armfield, Steven William We present a lattice Boltzmann (LB) method using a rectangular, non-isotropic lattice based on D2Q9 and D3Q27 velocity sets in two and three dimensions. A second order multi-scale expansion ensures that the scheme correctly reproduces hydrodynamic behaviour. A novel set of basis vectors is introduced in order to allow independent adjustment of eigenvalues corresponding to second order moments as required in order to ensure correct hydrodynamic behaviour using the non-isotropic lattice. Errors are reduced compared to other rectangular grid implementations. Linear perturbation analysis indicates that our scheme has similar stability properties to the isotropic LB method. We investigate the error behaviour of our scheme by performing Taylor-Green vortex flow simulations and comparing our results to simulations using a square grid and also to analytical results. We demonstrate that our scheme is well suited to direct numerical simulation of wall bounded turbulent flows and compare to well known benchmark results.

Destratification of thermally stratified turbulent open-channel flow by surface cooling

2026-04-28T02:43:41Z

Destratification of thermally stratified turbulent open-channel flow by surface cooling Kirkpatrick, Michael Philip; Williamson, Nicholas; Armfield, Steven William; Zecevic, Vanja Destratification of thermally stratified open-channel flow by surface cooling is investigated using direct numerical simulation. The initial states are the equilibrium states resulting from radiative heating. Using these states as initial conditions, a series of direct numerical simulations was run with radiative heating removed and a constant, uniform cooling flux applied at the upper surface. The flow evolves until the initial stable stratification is broken down and replaced by unstable stratification driven by surface cooling. The destratification process is described with reference to the evolution of the internal structure of the turbulent flow field. Based on these observations, we conclude that the dominant time scales in the flow from the perspective of destratification are the time scales associated with shear tτ , convection t∗ and stable density stratification tN . Scaling arguments are then used to derive a scaling relationship for destratification rate as a function of a friction Richardson number Riτ=(tτ/tN)^2 and a convection Richardson number Ri∗=(t∗/tN)^2 . The relationship takes the form DN=C1Riτ^−1+C2Ri∗^−1 , where DN is the destratification rate non-dimensionalised with respect to tN and C1 and C2 are model coefficients. The relationship is compared with simulation results and is shown to accurately predict the destratification rate in the simulations across a range of parameters. This relationship is then integrated to give a formula for the time taken for the flow to destratify.

Effect of an upstream grid on the fluidization of pharmaceutical carrier powders

2026-05-07T02:24:23Z

Effect of an upstream grid on the fluidization of pharmaceutical carrier powders Elserfy, Khalid; Kourmatzis, Agisilaos; Chan, Hak-Kim; Walenga, Ross; Cheng, Shaokoon The influence of grid generated mixing on the fluidization of pharmaceutical carrier powders 15 is studied in a channel-flow experiment using direct high-speed imaging and particle image 16 velocimetry (PIV). Four different lactose powders with mass median diameters that range 17 between 61μm to 121μm are used. The degree of powder mixing in the flow as a function of 18 grid position relative to the powder bed and grid area blockage ratios (ranging from ~25% to 19 ~40%) is studied for a range of flow-rates. The study presents comprehensive mappings of how 20 pharmaceutical powders are fluidised under the influence of mixing, by examining powder bed 21 morphology, powder emptying rate, and the local flow-field surrounding the pocket. The use 22 of a grid results in higher evacuation percentages (void fraction) and a faster evacuation rate 23 but is associated with randomized evacuation behaviour as observed from the powder bed 24 morphology. Use of a grid can enable evacuation of powder at lower overall flow-rates, which 25 may have important implications on respiratory drug delivery. PIV results show the trend of 26 mean velocities with the mass median powder diameter and demonstrates how a grid with 27 lower blockage ratio can increase the degree of mixing of the evacuating powder and make the 28 evacuation process more rapid. This study contributes towards a better understanding of 29 fluidization processes as relevant to dry powder inhaler devices and sheds light on how simple 30 design alterations, such as adding an upstream grid, can be incorporated to optimise device 31 effectiveness.

The effects of upper airway tissue motion on airflow dynamics

2026-05-07T02:24:25Z

The effects of upper airway tissue motion on airflow dynamics Zhao, Yongling; Raco, Joel; Kourmatzis, Agisilaos; Diasinos, Sammy; Chan, Hak-Kim; Yang, Runyu; Cheng, Shaokoon The human upper airway is not only geometrically complex, but it can also deform dynamically as a result of active muscle contraction and motility during respiration. How the active transformation of the airway geometry affects airflow dynamics during respiration is not well understood despite the importance of this knowledge towards improving current understanding of particle transport and deposition. In this study, particle image velocimetry (PIV) measurements of the fluid dynamics are presented in a physiologically realistic human upper airway replica for i) the undeformed case and ii) the case where realistic soft tissue motion during breathing is emulated. Results from this study show that extrathoracic wall motion alters the flow field significantly such that the fluid dynamics is distinctly different from the undeformed airway. Distinctive flow field patterns in the physiologically realistic airway include i) fluid recirculation at the back of the tongue and cranial to the tip of the epiglottis during mid-inspiration, ii) horizontal and posteriorly directed flow at the back of tongue at the peak of inspiration and iii) concentrated flow directed towards the root of tongue near to the end of inspiration. These findings suggest that the active deformation of the human upper airway can potentially influence particle transport by increasing deposition at the back of the tongue and therefore, highlights the importance of considering extrathoracic wall motion in future airway flow studies.

Does Upper Airway Deformation Affect Drug Deposition?

2026-05-07T02:24:29Z

Does Upper Airway Deformation Affect Drug Deposition? Cheng, Shaokoon; Kourmatzis, Agisilaos; Mekonnen, Taye; Gholizadeh, Hanieh; Raco, Joel; Tang, Patricia; Chan, Hak-Kim Knowledge that enables the accurate simulation of drug deposition in the human upper airway is necessary to develop robust platforms for efficient drug delivery by inhalation devices. The human upper airway is deformable during inhalation but how it could affect deposition of inhaled drugs is unknown. We aimed to determine whether pharyngeal deformation at the soft palate level will have any significant effects on throat deposition, in vitro lung dose and fine particle fraction. In this study, dry mannitol powders were delivered to the next-generation cascade impactor (NGI) through the United States Pharmacopeia (USP) throat, and a realistic upper airway cast (RUPAC) at flow rates of 20 40, 60 and 80 Lmin-1. Deformation of the upper airway at 25%, 50%, and 75% in the lateral and antero posterior directions were experimentally simulated in the RUPAC. Throat deposition (p = 0.04) is significantly affected when the upper airway deforms laterally but not antero-posteriorly.

Electrical and transient atomization characteristics of a pulsed charge injection atomizer using electrically insulating liquids

2026-05-07T02:24:24Z

Electrical and transient atomization characteristics of a pulsed charge injection atomizer using electrically insulating liquids Kourmatzis, Agisilaos; Shrimpton, John Charge injection atomizers are energy efficient devices that can be used in order to promote the atomization of dielectric liquids, and a potential application of such devices is fine spray delivery in small internal combustion engines. The operation of a pulsed charge injection atomization system operating at practical engine frequencies under a high voltage pulse train has not been well recorded in the literature. This initial investigation defines the electrical and transient global atomization performance of a charge injection atomizer operating under a steady flow regime, but with a typical high voltage pulse train. Results show that voltage-current characteristics follow similar trends to that of a steady flow, steady voltage system, and observation of the data also reveals that output current waveforms depend on the input pulse train frequency. No degradation in charging efficiency was observed at higher frequencies, which suggests that a charge injection atomizer can operate efficiently at practical engine speeds. Photographs also confirmed the high voltage pulse train injects charge that produces sections of primary atomization on the continuous liquid jet.

Multimodal learning and inference from visual and remotely sensed data

2026-04-28T02:43:38Z

Multimodal learning and inference from visual and remotely sensed data Rao, Dushyant; De Deuge, Mark; Nourani-Vatani, Navid; Williams, Stefan Bernard; Pizarro, Oscar Autonomous vehicles are often tasked to explore unseen environments, aiming to acquire and understand large amounts of visual image data and other sensory information. In such scenarios, remote sensing data may be available a priori, and can help to build a semantic model of the environment and plan future autonomous missions. In this paper, we introduce two multimodal learning algorithms to model the relationship between visual images taken by an autonomous underwater vehicle during a survey and remotely sensed acoustic bathymetry (ocean depth) data that is available prior to the survey. We present a multi-layer architecture to capture the joint distribution between the bathymetry and visual modalities. We then propose an extension based on gated feature learning models, which allows the model to cluster the input data in an unsupervised fashion and predict visual image features using just the ocean depth information. Our experiments demonstrate that multimodal learning improves semantic classification accuracy regardless of which modalities are available at classification time, allows for unsupervised clustering of either or both modalities, and can facilitate mission planning by enabling class-based or image-based queries.

Bounding Drift in Cooperative Localisation Through the Sharing of Local Loop Closures

2026-04-28T02:43:43Z

Bounding Drift in Cooperative Localisation Through the Sharing of Local Loop Closures Toohey, Lachlan; Pizarro, Oscar; Williams, Stefan Bernard Handling loop closures and intervehicle observations in cooperative robotic scenarios remains a challenging problem due to data consistency, bandwidth limitations and increased computation requirements. This paper develops a general cooperative localisation and single vehicle Visual SLAM framework that includes direct intervehicle observations and pose to pose loop closures on each vehicle with states shared as required. This fuses single vehicle SLAM with cooperative localisation and avoids data association of map data across limited communication networks. The base problem is developed as a factor graph with each vehicle solving local subgraphs that are split based on intervehicle observations. We modify the order of variable elimination in subgraphs through manipulation of the square-root of the Information matrix to extract updates that include the historic states involved in the loop closures and do not require transmission of other states not involved in the measurement or retransmission of previously shared states. We demonstrate the effect on localisation accuracy and bandwidth using data captured from a set of five robots observing each other and landmarks compared to both single vehicle SLAM, pure cooperative localisation and a centralised solution.

Adaptive path planning for depth‐constrained bathymetric mapping with an autonomous surface vessel

2026-04-28T02:43:43Z

Adaptive path planning for depth‐constrained bathymetric mapping with an autonomous surface vessel Wilson, Troy; Williams, Stefan Bernard This paper describes the design, implementation, and testing of a suite of algorithms to enable depth‐constrained autonomous bathymetric (underwater topography) mapping by an autonomous surface vessel (ASV). Given a target depth and a bounding polygon, the ASV will find and follow the intersection of the bounding polygon and the depth contour as modeled online with a Gaussian process (GP). This intersection, once mapped, will then be used as a boundary within which a path will be planned for coverage to build a map of the bathymetry. Efficient methods are implemented enabling online fitting, prediction and hyperparameter optimization within the GP framework on a small embedded PC. New algorithms are introduced for the partitioning of convex polygons to allow efficient path planning for coverage. These algorithms are tested both in simulation and in the field with a small twin hull differential thrust vessel built for the task.

Towards Adaptive Benthic Habitat Mapping

2026-04-28T02:43:44Z

Towards Adaptive Benthic Habitat Mapping Shields, Jackson; Pizarro, Oscar; Williams, Stefan Bernard Autonomous Underwater Vehicles (AUVs) are increasingly being used to support scientific research and monitoring studies. One such application is in benthic habitat mapping where these vehicles collect seafloor imagery that complements broadscale bathymetric data collected using sonar. Using these two data sources, the relationship between remotely-sensed acoustic data and the sampled imagery can be learned, creating a habitat model. As the areas to be mapped are often very large and AUV systems collecting seafloor imagery can only sample from a small portion of the survey area, the information gathered should be maximised for each deployment. This paper illustrates how the habitat models themselves can be used to plan more efficient AUV surveys by identifying where to collect further samples in order to most improve the habitat model. A Bayesian neural network is used to predict visually-derived habitat classes when given broad-scale bathymetric data. This network can also estimate the uncertainty associated with a prediction, which can be deconstructed into its aleatoric (data) and epistemic (model) components. We demonstrate how these structured uncertainty estimates can be utilised to improve the model with fewer samples. Such adaptive approaches to benthic surveys have the potential to reduce costs by prioritizing further sampling efforts. We illustrate the effectiveness of the proposed approach using data collected by an AUV on offshore reefs in Tasmania, Australia.

Pairwise comparison locomotion scoring dataset for dairy cattle

2026-04-28T03:07:51Z

Pairwise comparison locomotion scoring dataset for dairy cattle Gardenier, John; Underwood, James; Weary, D. M.; Clark, C. E. F. Lameness in dairy cattle is conventionally assessed through subjective, and often inconsistent visual scores of locomotion. Our work presents a pairwise comparison method to assess locomotion in cattle to reduce these sources of error. Five observers scored 50 videos of dairy cattle with conventional 4-level locomotion scoring and scored 90 pairs sampled from these 50 with pairwise scoring. Scaling methods were used to estimate a continuous measure of lameness for each video from the pairwise scores, which was compared to conventional scoring. This dataset contains the videos and scores used in this research.