Force identification by vorticity fields: Techniques based on flow imaging

Oscillation of a cylinder in quiescent fluid gives rise to complex patterns of vortices, which are related to the forces on the cylinder. Quantitative imaging of these patterns via high-image-density particle image velocimetry allows determination of the instantaneous distributions of vorticity. By considering the vorticity at successive instants of time, it is possible to identify the contributions to the instantaneous lift using two concepts: the extended Blasius theorem, and the Lighthill impulse concept. This approach represents the first prediction of force based on experimental distributions of instantaneous vorticity. (C) 1996 Academic Press Limited