Immersed Boundary Method for Aerodynamic Simulations of Complicated Rotorcraft Configurations

Abstract

Complete helicopter configurations in hover and forward flight conditions are numerically studied using an immersed boundary method and an actuator surface method. Detached eddy simulations are performed where the fuselage is modelled by the immersed boundary method, while the rotors are represented using the actuator surface method. Both generic and complicated rotorcraft configurations are investigated, where most of the geometrical details, such as the engine intake and exhaust, doors, struts, and wheels, are included. The immersed boundary method is a non-body-conformal mesh approach that allows a fully automated meshing process utilising a simple Cartesian mesh. Hence, this method is suitable for this purpose.

Four improvements are suggested for the immersed boundary method to enhance its computation speed and accuracy of the solution. These are implemented and validated for a turbulent flat plate, isolated fuselage, and unsteady ship airwake simulations. With the complete helicopter configurations, both isolated rotor and rotor-fuselage cases are studied to measure rotor performance and fuselage effect on the performance. The validation of each test case is conducted against both experimental measurements and computational data from the literature. The surface pressure, fuselage drag and download, unsteady rotor blade loadings, and power spectral density of the ship airwake over the flight deck are compared. Qualitative data demonstrate massive flow separation and recirculation from the bluff bodies (fuselage and ship) as well as rotor-fuselage and main rotor-tail rotor interactions. The computational effort for different grid levels of each test case is provided. Overall, the results have demonstrated an equivalent level of accuracy compared to the previous high-fidelity simulation results at their fraction of setup and computational expenses.