Breakdown of a Crossflow Vortex in a Three-Dimensional Boundary Layer
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Transition to turbulence in a three-dimensional boundary layer is investigated by a highly resolved direct numerical simulation which has been adapted to a swept flat plate transition experiment performed at DLR Göttingen. As shown earlier, our temporal simulation results can be related to the spatial disturbance development in the experiment and show a good agreement with measurements. The crossflow vortices, which develop as a primary instability of the laminar flow, break down at the late stages of the transition process. At the end of transition, the shape factor and the local skin friction coefficient of the computed mean velocity profile reach their turbulent levels. Particular attention is given to the development of flow structures in the breakdown stage. A new three-dimensional vortical structure is found to emerge which propagates with approximately 70% of the free-stream velocity in the streamwise direction. Vortical structures are identified by different criteria based on local pressure minima or the velocity-gradient tensor ∇u.
KeywordsVortical Structure Secondary Instability Primary Instability Parabolized Stability Equation Parabolized Stability Equation
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