Dynamic Stall Modeling Using Viscous Vortex Particle Method for Coaxial Rotors

Abstract

Dynamic stall is an important source of vibrations on a rotor at high advance ratios. The periodic flow separation and reattachment during dynamic stall generates large unsteady loads. In this study, the flow separation is modeled as the shedding of concentrated vorticity from the leading edge of the airfoil. The viscous vortex particle method is used to calculate the evolution of the rotor wake. Blade loads are calculated using a reduced order model obtained from computational fluid dynamics, and dynamic stall loads are calculated using the ONERA dynamic stall model. Results are presented for single main rotor and coaxial rotors at advance ratios of μ = 0.3–0.4. The separated wake modifies the angle of attack distribution on the rotor and hence impacts the hub loads. The results indicate that the separated wake modifies the vibratory hub loads by 5–10% for a single main rotor at μ = 0.3. The vibratory hub loads for the coaxial rotor are modified by 10–20% at μ = 0.4 with the inclusion of the separated wake. The upper and lower rotor tip path planes are tilted such that the blade and wake interaction is greater on the retreating side of the upper rotor and decreased on the advancing side.