Space-time imaging of a turbulent near-wake by high-image-density particle image cinematography

A cinematographic system allows acquisition of high-image-density PIV images in the cross-flow plane of the near-wake of a cylinder at a Reynolds number of 10 000. Images were acquired at a temporal resolution corresponding to 1% of the period of formation of the large-scale spanwise (Karman) vortices. Such a sequence of images leads to three-dimensional space-time representations, which show the relationship between the instantaneous concentrations of streamwise vorticity and the phase of formation of the large-scale Karman vortices. The first spatial correlations of instantaneous streamwise vorticity, taken over the cross-flow plane, reveal that the predominant concentrations of streamwise vorticity maintain a spanwise wavelength of approximately one cylinder diameter. (C) 1996 American Institute of Physics.