Noncirculatory Force on a Finite Thickness Body Encountering a Gust

Abstract

The origin of the noncirculatory force arising during a cylinder sharp-edged gust encounter is investigated experimentally at a Reynolds number of 6000. Planar particle image velocimetry and force balance measurements are employed simultaneously to assess the response of a translating cylinder encountering nominal gust ratios of 0.5, 1, and 1.5. Although the vortex sheet distribution, which represents the boundary-layer vorticity, agrees with that calculated following Küssner’s potential flow approach for a sharp-edged transverse gust, it was found that the sheet can also be determined from the vorticity distribution in the shear layers forming the gust edges. Furthermore, it is found that the noncirculatory force calculated using Küssner’s model is an overestimate because the implicit assumption of rigid gust shear layers leads to an unphysical additional momentum change as a body of volume enters the gust regime. A volume correction is therefore proposed. In addition, it is found that the gust shear layer width and deformation have a noticeable effect on the unsteady noncirculatory force development, which reduces the applicability of Küssner’s method for large gust ratios and objects with considerable volume.