M. Kloker, U. Rist
Institut für Aerodynamik & Gasdynamik,
Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Delaying laminar-turbulent transition undoubtedly reduces the skin friction at the wall and hence allows to diminish fuel consumption in many flows of practical interest. However, designing and optimizing devices for drag reduction requires a fundamental understanding of transition mechanisms and phenomena.
The results presented here contain a visualization of so-called Λ-vortices and their breakdown into smaller Ω-shaped vortices during the transition process next to the wall (placed at Y=0 in the figure below). Only a subregion of the integration domain used for a numerical solution of the complete incompressible Navier-Stokes equations employing a combined spectral/finite-difference algorithm developed at Institut A für Mechanik (until 1989) and then at Institut für Aerodynamik und Gasdynamik at the University of Stuttgart is shown. Here, a simulation has been performed using 65 spectral modes in Z direction on a X x Ygrid with 190,000 nodes. The number of unknowns at each time instant thus amounts to 74x106 and, starting from an initially laminar flow, approx. 7,000 time steps have been computed in order to capture the small-scale unsteady motions. The numerical results have been extensively verified by grid-refinement studies and validated by comparisons with stability theories and available experimental data.
These studies are part of ongoing research funded by Universität Stuttgart, Deutsche Forschungsgemeinschaft, Deutsche Volkswagen-Stiftung, and the European Community through INTAS.