Shock wave interaction with a spiral vortex

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 th e trailing edge of an aerofoil. In this study a bifurcated shock tube facil ity has been constructed where two plane waves arrive sequentially at the t railing edge of a wedge. The first shock wave results in a spiral vortex be ing shed, which is then impacted by the second wave. Accurate control of th e 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 d evelopment of a transient pressure spike, physically occupying an area less than 0.5 mm in diameter and having a duration of 15 mus, with a pressure n early two-and-a-half times that of the surrounding fluid. This has been don e both numerically using an adapting mesh Euler code, and experimentally, t he latter with the careful use of fast response miniature pressure transduc ers. Numerically generated holographic interferograms and shadowgraph image s have been generated for direct visual comparisons with the equivalent exp erimental results of the whole flow field, from which the reason for the pr oduction of the pressure spike is established as being due to local shock w ave focusing resulting from part of the shock being pulled around the vorte x to impact on itself. The generation of a second pressure peak is also exa mined, as is the wave field emanating from the interaction and the influenc e on the vortex. The use of both experimental images and numerical flow vis ualization algorithms were found to provide complimentary information, whic h allowed for detailed investigation and understanding of the shock wave-vo rtex interaction. (C) 2001 American Institute of Physics.