Computer-aided flow visualization and vorticity balance in the laminar wake of a circular cylinder

The two-dimensional Navier-Stokes equations were used for the solution of laminar vortex shedding behind a circular cylinder at a Reynolds number of 106 using the finite element technique. Streamlines, equivorticity lines and filament lines have been used for the wake visualization, while the pressure distribution in the wake is presented in the form of isobars. Useful conclusions have been drawn from the superposition of different flow visualization patterns, a technique used extensively herein. The strengths of the laminar vortices were calculated at various locations from the vorticity distribution, confirming the hypothesis that maximum strength occurs at the end of the formation region. A vorticity balance in the cylinder wake was conducted, comparing the circulation influx into the wake over a period and the strength of the vortices. The time-dependent streamwise fluid velocities were calculated from the present simulation at various points in the wake, and are presented on the same diagram with velocities measured experimentally at similar conditions. The validity of alternative definitions for the vortex formation length was examined and the velocity and displacement of the newly formed vortex as function of time was calculated. (C) 1997 Academic Press Limited.