Shock wave interaction with a spiral vortex

Abstract

Previous studies on shock–vortex interactions have either been numerical in nature with idealized boundary conditions and prescribed vortex flows, or in complex experimental flow fields, such as where the vortex is shed at the trailing edge of an aerofoil. In this study a bifurcated shock tube facility has been constructed where two plane waves arrive sequentially at the trailing edge of a wedge. The first shock wave results in a spiral vortex being shed, which is then impacted by the second wave. Accurate control of the delay between the two shock waves was achieved using a highly repeatable piston actuated shock tube driver. A number of interesting new features of this interaction have been identified. The work specifically examines the development of a transient pressure spike, physically occupying an area less than 0.5 mm in diameter and having a duration of 15 μs, with a pressure nearly two-and-a-half times that of the surrounding fluid. This has been done both numerically using an adapting mesh Euler code, and experimentally, the latter with the careful use of fast response miniature pressure transducers. Numerically generated holographic interferograms and shadowgraph images have been generated for direct visual comparisons with the equivalent experimental results of the whole flow field, from which the reason for the production of the pressure spike is established as being due to local shock wave focusing resulting from part of the shock being pulled around the vortex to impact on itself. The generation of a second pressure peak is also examined, as is the wave field emanating from the interaction and the influence on the vortex. The use of both experimental images and numerical flow visualization algorithms were found to provide complimentary information, which allowed for detailed investigation and understanding of the shock wave–vortex interaction.