Calculation of free-wake of forward flying rotor in ground effect

A free-wake based model was developed to predict the flow field and performance of a forward flying rotor in ground effect.In order to expand the application range of the model,the ground was modeled using surface panel method to simulate the influence of ground upon the flow field.For further improving the prediction convergence and accuracy,modification measures such as rectifying the wake vortices below the ground plane proportionally and distributing the ground panels circularly were incorporated into the model.The prediction results show that as the advance ratio increases,the flow regime below the rotor changes from recirculation to ground vortex mode.When rotor gets into the recirculation regime at extremely low advance ratio,the downwash velocity across rotor leading edge is very large.Which leads to an unexpected phenomenon that the rotor thrust decreases and the required rotor power almost keeps constant while the advance ratio increases.The predicted characteristic values of rotor aerodynamics at different advance ratios were then compared with experimental results and conformed well,proving the accuracy of the newly founded model.