A Near Wake Dynamic Model

A near wake model has been developed to meet the requirements of three dimensional blade/vortex interaction computation. The use of indicial lift functions means that shed vorticity is implicitly accounted for, thus only the time varying trailing system remains to be evaluated. The basic calculation for the velocity induced by a line vortex has been re-formulated in such a manner that the integrated effect of time varying strength may be readily accomodated within a simple and efficient numerical solution. Some idealised applications to time varying lift on a wing are used to illustrate the implications of the approach and extended to coupled lift/downwash solutions to demonstrate the satisfactory implementation of the numerical procedures. Comparison is made with a wind tunnel test of blade/vortex interaction to show the three dimensional and temporal effects in a rotating system. Finally, the results are shown of a rotor loads calculation which involves interaction with the far wake so as to produce a "blade slap" signal.