Buffeting of fin - Distortion of incident vortex

Abstract

The encounter of a broken-down vortex with the swept leading edge of a fin is investigated in a water channel using high-image-density particle image velocimetry, which leads to instantaneous fields of velocity and vorticity. The vortex-fin interaction generates a layer of time-averaged vorticity extending along the entire leading edge from the root to the tip of the fin. This averaged vorticity is actually due to a succession of instantaneous states of highly concentrated vorticity along the edge of the postbreakdown region of the vortex. Above the surface of the fin, however, the averaged vorticity has a relatively low level ; the corresponding instantaneous vorticity concentrations have alternating sign and are not repetitive in space or time. Nevertheless, two-dimensional correlations of instantaneous vorticity exhibit well-defined peaks corresponding to an identifiable wavelength between the vorticity concentrations. Spectra of surface pressure at crucial locations on the fin are related to these features of the instantaneous and averaged flow structure.