Flow Simulations Past Helicopters at Different Flight Conditions using Low and High Order CFD Methods

摘要

The present paper contains a comprehensive literature survey on helicopter flow analyses and describes some true unsteady flows past helicopter rotors obtained using low and high order CFD models.The low order model is based on a panel method coupled with a viscous boundary layer approach and a compressibility correction.The USAERO software is used for the computations.The high order model is based on Euler and Navier- Stokes equations.For the high order models,a true unsteady scheme,as implemented in the CFD- FASTRAN code using the Euler equations,is considered for flows past hovering rotor.On the other hand,a quasi-steady approach,using the WIND code with the Navier-Stokes equations and the SST turbulence model,is used to assess the validity of the approach for the simulation of flows past a helicopter in forward flight conditions.When using the high order models,a Chimera grid technique is used to describe the blade motions within the parent stationary grid.Comparisons with experimental data are performed and the true unsteady simulations provide a reasonable agreement with the available experimental data.The panel method and the quasi- steady approach are found to overestimate the loads on the helicopter rotors.The USAERO panel code is found to produce more thrust owing to some error sources in the computations when a wake-surface collision occurs,as the blades interact with their own wakes.The automatic cutting of the wake sheets,as they approach the model surface,is not working properly at every time step.