Predictions of Airloads and Wake Geometry for Slowly Starting Rotor Blades in Hovering Flight by Using Time Marching Free Vortex Blob Method

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. Calculations are also carried out on a coaxial rotor.