Coupled Analysis between CFD and CSD for a Helicopter Rotor in Hover and Forward Flight

This paper presents a combination of an analysis between a computational structural dynamics (CSD) and high fidelity unsteady computational fluid dynamics (CFD) analysis. Regarding a helicopter in hover, aerodynamic loads are computed from the three-dimensional Navier-Stokes solver in overlapped grids, and blade motions are estimated from the geometrically exact rotor beam analysis. While combining those two analyses, a loosely coupled method is used and the results are validated regarding a civil transport helicopter. The next step is to analyze a periodic steady-state flight condition such as forward flight. In this paper, HART II blade flapping motion in a forward flight acted upon by periodic airloads and collective pitch angle is predicted by using a similar procedure as is used in hover. But the response phase is obtained to be different from that observed in the experiment. Thus, a further consideration upon the periodic excitation forces and the blade response will be required in the foregoing CFD and CSD computation for forward flight. Nomenclature Mtip = hover tip Mach number c = chord length CnM2 = sectional normal force Cp = pressure coefficient CT = thrust coefficient Ct = sectional thrust coefficient R = radius of rotor blade σ = solidity μ = advance ratio ψ = azimuth angle θ = blade pitch angle γ * = force strain κ * = momentum strain I