Inviscid cavity flow over a wall-mounted fence

Abstract

Two-dimensional cavitating flow over a sharped-edged wall-mounted fence is investigated using inviscid analysis. Similar devices are used for lift generation or enhancement on the trailing edges of aero- and hydrofoils (Gurney flaps, spoilers) or ship transoms (interceptors). The sharp edge induces stable flow/cavity detachment, with lift resulting from the surface pressure distribution acting on the wall upstream of the fence. Analytical and numerical results are presented and compared from which the ‘ideal’ maximum hydrodynamic performance of such devices is obtained. The upstream wall pressure distribution reduces rapidly initially, then eventually as a power law relation in the far field. As the relative cavity pressure is reduced and hence also the cavity length from the infinite upper bound, there is a corresponding reduction in magnitude of the pressure distribution. An ‘ideal’ maximum hydrodynamic efficiency (Lift/Drag)) of greater than 40 is obtained with both cavity and upstream wall of infinite length. For a finite wall length of practical size this value reduces to about 15. Within the limits of 2-D inviscid analysis these results give the upper bound to the hydrodynamic performance possible and general character of cavitating flow over a sharped-edged wall-mounted fence.