Investigation of Unsteady Aerodynamics on Rotor Wake Effects in Maneuvering Flight

The role of unsteady effects on the maneuvering aerodynamics of a helicopter rotor has been investigated. The work was focused toward an improved understanding of the underlying aerodynamic mechanisms that may be responsible for the ‘off-axis’ response problem found on helicopters. The approach used a free-vortex wake model, which explicitly tracks the vortical elements of the rotor wake. Different forms of unsteady aerodynamic representations were integrated into the free-wake simulation. A simple quasi-steady aerodynamic model was used as a baseline. The use of a conventional blade element unsteady aerodynamics model based on the indicial method was also incorporated. The indicial method represents, in part, the unsteady effects associated with the shed wake downstream of the blade, and implicitly includes compressibility effects. The effects of unsteady aerodynamics were also included by explicitly tracking shed vortical wake filaments as part of the complete free-wake solution. The results have shown that the effects of unsteady aerodynamics on the predictions of the rotor wake geometry and inflow are relatively small, and are unlikely to be a primary contributor to the off-axis response problem.