Fast Free Wake: a Possible Approach to Real-Time Rotor Wake Simulation

Accounting for wake-body interference effects in real-time simulations is still a challenge. To this aim the Fast Free Wake (FFW) model has been developed. It consists in a simple elaboration of the free-wake concept: vortex rings are released every certain time step from the rotor disk, and then they are free to move, interacting with all the other vorticity sources in the flow field without constraints. Wake deformation is accounted for by rings movement and diameter variation, while vorticity strength is directly related to the instantaneous rotor thrust value. The model has been developed, implemented, and then validated in hover, forward flight, vertical flight both In Ground Effect (IGE) and Out of Ground Effect (OGE). The computational efficiency of the model has been deeply investigated and the real-time running capability has been confirmed. The low computational cost required by FFW, together with its fair accuracy, makes the proposed model a valid tool for real-time flight mechanics simulations.