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Oliver Thomer
Aerodynamisches Institut der RWTH-Aachen

The picture shows vortex breakdown, enforced by the interaction of a normal shock and a slender vortex with its axis parallel to the oncoming supersonic flow. The phenomena was numerically simulated with a finite-volume solution of the Navier-Stokes equations for time-dependent, compressible, viscous flow. The conservation equations were written in divergence form, with the time derivatives discretized with a Runge-Kutta five-step scheme, and the spatial derivatives with a node-centered finite-volume technique. A cartesian grid was used with clustering of grid points near the axis of the vortex. The total number of grid points was 2 millions. Computations were carried out for a free-stream Mach number Ma=1.6 and a Reynolds number Re=15000, based on the initial vortex core radius. The inflow profile of the azimuthal velocity component was prescribed by a BurgersŤ vortex with the circulation Gamma=2.5, non-dimensionalized with the vortex core radius and the stagnation speed of sound. The inflow profile for the axial velocity component was assumed to be Gaussian with a velocity defect of 10 percent. The temperature distribution was computed from isentropic relations. The figure shows the flow downstream from the normal shock, visualized by the plane normal to the vortex. The breakdown process is characterized by vortex shedding immediately downstream from the shock and subsequent spiraling of the inner part of the core. The iso-surfaces shown represent surfaces of constant pressure.

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