Numerical simulations of the unsteady flowfield of helicopter rotors on moving embedded grids

Abstract

An Euler solver was developed for the prediction of 3-D unsteady flow phenomena that occur on helicopter rotors in forward flight, based upon a cell-centered finite volume approximation and dual-time method. In order to reduce false diffusion of vorticity and account for the rigid blade motions in rotation, flapping and pitching, a moving embedded grids methodology was adopted. Aiming at the key identification issue of donor elements in embedded grids, the present analysis implements a new searching scheme, the Pseudo-Searching Scheme of Donor Elements (PSSDE), for improvement purposes. The efficient dual-time method and moving embedded grids methodology make it feasible to compute the complicate flowfield of helicopter rotors on typical PC computers. Preliminary simulation results on surface pressure distributions were presented for a two-bladed Caradonna model rotor in forward flight at different collective pitch angles and flapping angles. Good agreements are found with measurements or other calculated results. Then unsteady lifting results, simulated for three different blade tip planforms, demonstrate the benefit of swept tips in suppressing supercritical flow. Additionally, the vorticity magnitude contours give some qualitative pictures on the evolvement of the distorted rotor wake.