Experimental Investigation of Pairs of Vortex Filaments in Ground Effect

Abstract

The motion of co -rotating filaments in ground effect is investigated using a water tunnel. The vortices are generated using two flat blades and the ground is modeled with a splitter plate. The time history of the vortex motion is recorded at several downstream locations. Data is shown for two ground plane positions and compared with the vortex be havior in the free stream. The experimental data is also verified using a potential -flow model. Results show that the vortices undergo a rebound as the result of ground effect. The vortices also undergo a lateral motion due to potential flow effects. A leapfrogging behavior is present due to the differences in the lateral motions caused by the ground proximities of the spiraling vortices. In addition, the filaments form planar waves and move along preferred directions. b = vortex span at the trailing edge of the blades C = chord max min , I I = principal second moments of vortex position N = total number of vortices Re � = vortex Reynolds number = � / � S = span � V = free stream velocity z