Direct Numerical Simulation of Shear-Induced Transitional Mixing and its Interplay with Combustion

Abstract

Turbulent mixing is central to advanced energy and propulsion technologies, yet its complexity presents challenges for control and prediction. This complexity stems from a high degree of interdependence of the different underlying physical processes and scales of fluid motion and is further exacerbated when the mixing process is afflicted by rapid compositional and fluid property changes such as with combustion or nuclear fusion. Prominent advancements in the field were mostly through experimental investigations. However, with the highly chaotic nature of turbulence and the limited diagnostics available to collect comprehensive data sets from experiments, additional significant advancements in the field stagnated. The recent improvement of computing and storage facilities enable through numerical simulations, access to comprehensive flow field information and the opportunity to artificially isolate elements of interdependent physics.

This thesis leverages High-Performance Computing to investigate how fundamental shear instabilities, namely Kelvin-Helmholtz Instabilities (KHI), drive turbulence generation and mixing, offering new insights for turbulence and combustion control. Through high-fidelity simulations, the role of initial perturbation parameters on flow and mixing evolution in both inert and reacting flows are explored and demonstrated to exhibit wide-reaching implications on both the flow and the mixing development well beyond the initial stages of flow perturbation. The findings challenge the traditional sole reliance on the Reynolds number to characterize the extent of turbulence and reveals new sensitivities of the flow evolution that extend to the stabilised flame structure. These results pave the way for more accurate predictions and optimized designs to control turbulent mixing in cutting-edge energy and propulsion technologies.