Flow-Structure Interactions on Helicopter Rotors in Forward Flight

Abstract

The flow field of a helicopter rotor in forward flight is highly three-dimensional and unsteady, it is transonic at the tip of the advancing side of the rotor and it suffers from possible dynamic stall and reverse flow at the retreating side. The rotor reacts to this unsteady and asymmetric inflow by flapping, lagging and oscillatory torsional motions. Since these motions influence the aerodynamics a coupled treatment of aerodynamics and rotor dynamics is mandatory. One possibility to numerically simulate this complex flow-structure interaction is to use coupling schemes that combine separate aerodynamics and dynamics modules. Each module can be highly sophisticated. The very important element in this case is the coupling algorithm that is responsible for the accuracy and the stability of the complete coupled procedure. The occurring flow conditions, blade motions and structural phenomena are discussed. The basic equations for both flow and dynamics and the corresponding numerical schemes are addressed to simulate the aerodynamics and the dynamics as well as the interference effects. It is shown that especially staggered coupling schemes of second order in time can be verified by a proper handling of the complete simulation tool which is mandatory for a time accurate simulation of the aeroelastic behavior of a helicopter rotor in forward flight. The accuracy of the complete scheme is demonstrated by comparison with wind tunnel tests.