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.