Free-wake analysis of tandem, tilt-rotor and coaxial rotor configurations

A free-wake model has been developed to predict the wake geometries of tandem, tilt-rotor and coaxial twin-rotor systems. The basic formulation is based on a pseudo-implicit, predictor-corrector, relaxation scheme with five-point central differencing and velocity averaging in space. Results are presented for three rotor configurations for several advance ratios ranging from relatively low speed to moderately high speed forward flight conditions. Comparisons have been made between computed and measured tip vortex geometries for the coaxial configuration, with good overall agreement.