New method for predicting rotor wake geometries and downwash velocity field

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized wake model, a semi-empirical correction for the vortex core effect on rotor wake is made and free wake calculation is carried out. As an example of its engineering application, the calculated downwash velocity field along the rocket launch line is presented and simply analyzed. In terms of theory, the method developed here may provide a referable basis for further study of the formation mode of the tip vortex and vortex core interior structure.