Neutrally-stratified boundary layer flows over a 2-D block: An LES study

Large-eddy simulation (LES) is adopted to simulate re-circulation flows associated to a 2D block in neutrally-stratified boundary-layer flows developed over rough and smooth surfaces. Three different subgrid-scale (SGS) models for SGS stresses are tested: (a) the Smagorinsky model, (b) the Lagrangian dynamic model, and (c) the scale-dependent (SD) Lagrangian dynamic model (Stoll and Porté-Agel, 2006). Simulation results obtained with the different models are compared with measurements obtained with hot-wire and cold-wire anemometry at the St. Anthony Falls Laboratory atmospheric boundary layer wind tunnel. We find that the Lagrangian scale-dependent dynamic model is able to account (tuning-free) for the local changes in the eddy-viscosity model coefficient. It can also capture the scale dependence of this coefficient associated with flow anisotropy at the smallest resolved and sub-grid scales in regions of the flow with strong mean shear. As a result, the scale-dependent dynamic model yields results that are more realistic than the ones obtained with the standard Smagorinsky model and the scale-invariant Lagrangian dynamic model.