Numerical analysis of helicopter rotor/fuselage unsteady aerodynamic interaction

Unsteady aerodynamic load on helicopter fuselage is mainly due to aerodynamic interaction of rotor and fuselage. An unsteady panel/time step full span-free wake method is established to accurately predict the rotor/fuselage unsteady aerodynamic interaction for the vibration load analysis of whole vehicle. The unsteady panel method is used to consider unsteady aerodynamics of rotors and fuselage, and the free-wake method is applied to accurately simulate dynamics of rotor wake. Helicopter fuselage is discretizated into source/doublet panels to simulate its lift in forward flight, and vortex line mirror method is adapted to account acceleration phenomenon resulted from rotor wake close to fuselage surface. To validate the accuracy of this approach, unsteady rotor/fuselage aerodynamic interaction of Maryland and ROBIN modes are simulated in forward flight, and compared with measured data and CFD results. Finally, the influences of advanced ratio, rotorfuselage distance on unsteady aerodynamic interaction are analyzed. It is shown that the unsteady pressure of fuselage is mainly affected by rotor blade pass effect, while that of tail boom is mainly due to the interaction of rotor wake and fuselage, and the frequency of unsteady pressure is times of blades number. Amplitude of unsteady pressure on fuselage will increase as advance ratio increases, that of tail boom, however, will increase and then decrease. Increasing rotorfuselage distance will decrease amplitude of unsteady pressure on fuselage and tail boom.