Numerical Simulation of Rotor Using Coupled Computational Fluid Dynamics and Free Wake

Abstract

Rotor aerodynamics is governed by wake behavior. Particularly, aerodynamic performance in the hovering flight condition is determined by the structure and the strength of the wake. In this paper, rotating blades were simulated using a tightly coupled computational fluid dynamics and time-marching free-wake method in hovering and forward flight. The rotating blades and a flowfield near the rotor are calculated by the computational fluid dynamics, and the strength and motions of the wake are simulated with the time-marching free-wake method. A moving overset grid technique is applied to consider rotor motions during hovering and forward flight. Inflow and outflow conditions in the computational fluid dynamics domain are provided from an induced flow rate by the time-marching free-wake method at each time step. The strength of the trailed vortices is determined from a sectional lift calculated in the rotating blade, which is computed using the computational fluid dynamics. The present coupled method was compared with other inflow and outflow conditions, such as source sink and Riemann-invariant conditions. To investigate the robustness of the present method, grid-size effects were also tested in large and small background grid systems.