Main/Tail Rotor Interaction under Ground Effect Using DLR 3D Free Wake Code

The prediction of the ground effect on rotor aerodynamics remains a challenging task for all wake models because of the complicated influence of the ground on the wake development. A numerical simulation of main rotor and tail rotor interaction operating in ground effect was carried out with two different ground models, an image and a surface singularity model. An unsteady free wake 3-D panel code developed at DLR has been extended to account for the ground effect. The effect of the ground on rotor interference versus height above ground was examined on the basis of the main and tail rotor wake development and corresponding loads. The study was conducted for a simultaneously rotated main/tail rotor configuration in hover and forward flight. The results with two different ground models were compared. The problem of using a surface singularity model is discussed.