AERODYNAMIC COMPUTATIONS APPLIED TO HELIC OPTERS

Applied aerodynamics analysis on helicopters require the availability of many computational methods: those used at ONERA are presented in th is paper. The first part consists of a description of the main aerodyn amic features of helicopters. The second part is devoted to the studie s on helicopters in forward flight configurations. The R85 dynamic cod e is one of the tools used at ONERA to calculate blade motion. Satisfa ctory results are obtained for blade motion, the power required by the main rotor and the distribution of forces and deformations, as long a s the blade geometry is not too complex. A more detailed description o f wake model is then given. The wake is modeled by vortex lattices (ME TAR code). For aeroacoustic calculations (low speed cases), the prescr ibed wake geometry is replaced by a free wake analysis (MESIR code), w hich provides better correlations with experimental data when blade/vo rtex interaction occurs. However, 2D methods are not accurate enough t o predict transonic flows on the advancing blade. That is why ONERA de veloped a full potential 3D unsteady code (FP3D) which is able to accu rately calculate the effect of blade planform changes. Some improvemen ts such as entropy corrections, boundary layer corrections and aeroela stic coupling are also described. For hovering flight, the wake model has to be refined because of the strong blade/vortex interactions. Lif ting-line methods can provide a first approximation of the power requi red by the rotor but are not accurate enough to compute advanced geome try rotors. A 3D method (PHOENIX) is used to obtain better results on such rotors. The presence of the fuselage can also significantly influ ence the main rotor wake. Special methods were developed to model this phenomenon. Generally, a panel method is used for the fuselage. For c alculation of the viscous flows, a boundary layer code (3C3D) was inte grated in this method.