Calculating method of helicopter rotor downwash flow field based on free wake analysis

A rotor free-wake model including fuselage effects was established to predict the rotor induced velocity flow field of a real helicopter which has a combined rotor and fuselage configuration, and to provide a calculating method of the downwash flow field for airborne rocket or missile fire. In this model, a rolled-up tip vortex model was used to simulate the effects of the wake on the flow field, a second-order lifting-line model was adopted to represent the effects of the blade on the flow field and a source panel model was included to take into account the induced and obstructed effects of the fuselage on the rotor wake. Based upon the free-wake model, numerical examples for a 4-blade combined rotor and fuselage configuration of University of Maryland and a 2-blade combined rotor and fuselage configuration of the Georgia Tech were given. The computations of steady and unsteady flow velocities were carried out. The comparison between calculated result and available experimental data shows the effectiveness of the method.