Pressures and Forces Induced by the Ground Vortex

When the jet stream from a fan or jet powered STOVL aircraft impinges on the ground during STOL operation, the part of the impinging flow that is directed forward is opposed by the free stream (fig. 1) and rolled up into a horseshoe shaped ground vortex. This ground vortex induces pressures on the lower side of the model that can significantly affect the forces and moments experienced in STOL operation.

Available methods for estimating the lift and moment induced by the ground vortex (ref. 1 - 2) are based primarily on force data. This paper presents a review of an ongoing analysis of the effects of the ground vortex that is based on detailed lower surface pressure distributions (ref. 3). The estimating method that is being developed is demonstrated using some comparisons with experimental data.