WHOLE-FIELD DENSITY VISUALIZATION AND ABEL RECONSTRUCTION OF AXISYMMETRIC VORTEX RINGS

摘要

We present a simple non-invasive optical measurement technique to obtain two-dimensional qualitative and quantitative visualizations of axisymmetric vortex rings. The CO_2-loaded vortex rings are generated using a piston/cylinder apparatus and can be characterized by a circulation-based Reynolds number, Re, and a piston stroke to orifice diameter ratio, I/D_o. Qualitative visualizations of the generated rings are obtained using the recently introduced Background-Oriented Schlieren (BOS) technique, and 2D whole-field density profile measurements are extracted using a PIV algorithm. In a final step, we implement an inverse Abel transform technique to reconstruct radial vortex ring profiles and to compare them with projection measurements. Reconstructed images of such profiles are well suited to visualize characteristic structures of vortex rings such as the recirculating spiral roll-ups and the trailing wakes.