Experimental studies on compressible leading-edge vortices

A review emphasizing the quantitative studies of leading-edge vortices at supersonic speed is presented. While quantitative investigations of vortical flow over delta wings are extensive in the incompressible regime, and to a degree in transonic range, their measurements in supersonic freestream are very scarce. It is illustrated that the existing knowledge of leading-edge vortices in the supersonic regime is mainly qualitative, compiled from large amount of flow visualization experiments. A brief account of the flow visualization studies is first presented, followed by a comprehensive survey of the various measurement attempts to quantify these vortices. On the qualitative side, this survey reveals that in spite of the past efforts, the literature still lacks a unified topological description of the compressible leeward vortical flows. In quantitative investigations, the experience with pressure probes and seed based optical measurement techniques is highlighted, and the associated results summarized. Amongst them, although there exists a topological similarity in the delta wing leeward flow at low- and high-speeds, available measurements suggest that leading-edge vortices in supersonic flow have a very different axial flow character. Additional salient features of leading-edge vortices in supersonic freestreams are also provided in the paper.