Rotor Wake Modeling for Flight Dynamic Simulation of Helicopters

A computational helicopter rotor wake model, based on the numerical solution of the unsteady fluid-dynamic equations governing the generation and convection of vorticity through a domain enclosing the helicopter, has been developed. The model addresses several issues of specific interest in the context of helicopter flight dynamic modeling. The problem of excessive numerical dissipation of vortical structure, common to most grid-based computational techniques, is overcome using a vorticity conservation approach in conjunction with suitable vorticity-flux limiter functions. Use of a time-factorization-type algorithm allows the wake model to avoid the stiffness that is introduced in flight dynamic applications by the disparity between the rotor and fuselage timescales and to generate rapid solutions to the time-varying vortical structure of the helicopter wake. The model is demonstrated to yield valid solutions to the blade loading and wake structure for isolated and interacting rotors in both hover and forward flight