AN EVALUATION OF A NAVIER-STOKES CODE FOR CALCULATIONS OF RETREATING BLADE STALL ON A HELICOPTER ROTOR

A hybrid time-marching technique for the numerical solution of the three-dimensional unsteady, Reynolds-averaged, Navier-Stokes equations has been used to compute the three-dimensional retreating blade stall characteristics on a helicopter rotor. An evaluation of the results from this solution is being carried out. Forces computed by the Navier-Stokes code are compared to results from a modularized, two-dimensional strip, blade element theory method that includes a free wake analysis module, an unsteady aerodynamics module, and an aeroelastic rotor module. Initial results from the three-dimensional Navier-Stokes analysis indicate that there is an outflow in the separated region of the retreating blade. This three-dimensional separation phenomenon generates forces that cannot be predicted by current state-of-the-art analysis codes that use two-dimensional airfoil stall characteristics to predict the rotor blade characteristics.