Numerical simulations of wake structure generated by rotating blades using a time marching, free vortex blob method

Abstract

Vorticity fields in the wake generated by rotating blades are calculated using a time-accurate, free vortex blob method without a non-physical model of the far wake. The computed free-wake geometry of single rotor in hover is represented by the three wake regions: well-defined tip vortex region, intermediate entangled region, and initially generated wake bundle. The air loads and simulated wake geometries in the radial and axial directions agree well with those obtained using a prescribed wake method for a one-blade rotor, and with the experimental data for a two-blade rotor. This agreement can be obtained with the correct initial condition of a slowly rotating blade instead of a impulsively rotating blade. The wake geometry and unsteady air loads of helicopter rotor in forward flight is also calculated. In forward flight, the rotor blade and wake interaction is critical to vibration and noise problem of helicopter. Because the computational time of the free vortex blob method is proportional to the square of element number, the reduction method of computational time is also considered.