Normal vortex interaction with a circular cylinder

Interaction of a columnar vortex. with a long circular cylinder translated normal to the vortex axis is examined for the case where the cylinder diame ter is much larger than the vortex core radius. The study focuses on unders tanding and quantifying the limitations of traditional vortex filament mode ls arising from vortex-induced separation of the cylinder boundary layer an d vortex core shape deformation. These limitations an: examined over a wide range of values of the impact parameter, defined as the ratio of the ambie nt normal velocity past the cylinder to the maximum vortex azimuthal veloci ty, Filament model predictions of vortex displacement are compared to exper imental data both before and after vortex-induced boundary-layer separation . Experimental data are presented showing the importance of the ambient nor mal velocity to the cylinder in delaying vortex-induced boundary layer sepa ration, so that far cases with high impact parameter the flow is governed b y inviscid effects even as the vortex moves quite close to the cylinder sur face, The inviscid shape deformation of the vortex core is modest in the ca ses examined, even for close vortex-cylinder interaction, and is shown to h ave small effect on the surface pressure, The topology of secondary vortici ty structures ejected from the cylinder boundary layer is examined using a two-color laser-induced fluorescence technique and is found to be qualitati vely different for cases with high and low values of the impact parameter.