LARGE-EDDY SIMULATION OF NONLINEAR EVOLUTION AND BREAKDOWN TO TURBULENCE IN HIGH-SPEED BOUNDARY-LAYERS

The nonlinear evolution and laminar-turbulent breakdown of a boundary- layer flow along a cylinder at Mach 4.5 is investigated with large-edd y temporal simulation. The results are validated using the direct nume rical simulation data of Pruett and Zang. The structure of the flow du ring the transition process is studied in terms of the vorticity field . The subgrid scales are modeled dynamically, where the model coeffici ents are determined as part of the solution from the local resolved fi eld. In the numerical simulation the dynamic-model coefficients are ob tained by using both the strain-rate contraction of Germane et al. and the least-squares contraction of Lilly; they produced some difference s in the details of the vorticity structure inside the transition regi on. A new dynamic model that utilizes the second-order velocity struct ure function is used to parametrize the small-scale field. The evoluti on to turbulence is successfully simulated with dynamic subgrid-scale modeling at least in terms of average quantities as well as vorticity fields. This is achieved with one-sixth of the grid resolution used in direct numerical simulation.