Large-Eddy Simulation of Transition to Turbulence in Boundary Layers

Large-eddy simulation (LES) results for laminar-to-turbulent transition in a spatially developing boundary layer are presented. The disturbances are ingested into a laminar flow through an unsteady suction-and- blowing strip. The filtered, three-dimensional time-dependent Navier-Stokes equations are integrated numerically using spectral, high-order finite-differences, and a three-stage low-storage Runge- Kutta/Crank-Nicolson time-advancement method. The buffer-domain technique is used for the outflow boundary condition. The localized dynamic model used to parametrize the subgrid-scale (SGS) stresses begins to have a significant impact at the beginning of the nonlinear transition (or intermittency) region. The flow structures commonly found in experiments are also observed in the present simulation; the computed linear instability modes and secondary instability lambda- vortex structures are in agreement with the experiments, and the streak-like structures and turbulent statistics compare with both the experiments and theory. The physics captured in the present LES are consistent with the experiments and the full Navier-Stokes simulation (DNS), at a signficant fraction of the DNS cost. A comparison of the results obtained with several SGS models shows that the localized model gives accurate results both in a statistical sense and in terms of predicting the dynamics of the energy- carrying eddies, while requiring fewer ad hoc adjustments than the other models.