Large-Eddy Simulation of Separation Control for Flow Over a Wall-Mounted Hump

Abstract

This work describes an implicit large-eddy simulation (LES) for active control of flow over a wall-mounted hump. Both steady suction and oscillatory blowing and suction are compared to baseline conditions with no flow control. This simulation models an experiment conducted by NASA which was one of the test cases in their 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop. A previous LES of the baseline case with the current scheme demonstrated significantly better agreement with the experimental flow physics than RANS in the separated region downstream of the hump. The current work concludes that this also holds for the cases using active control. The LES is accomplished using an implicit parallel flow solver that is based on an approximately-factored time-integration method using fourth-order spatial compact-dierence formulations and a high-order filtering strategy. To properly resolve the flow for this LES, the Reynolds number of 9.36 ◊ 10 5 used in the experiment was reduced to 2.0 ◊ 10 5 . Eects of lowering the Reynolds number were previously investigated using RANS. Flow features of the active control cases are compared with the baseline case, each other, and experimental data. The active control LES cases matches experimental data significantly better in the recirculation region than RANS. The baseline and steady suction LES separation reattachment lengths are within 2% and 4%, respectively, of the experimental locations. These simulations achieve very good agreement with the experimental surface pressure coecient, skin friction coefficient, mean velocity profiles, Reynolds stresses, and flow reattachment location. Because of the lower Reynolds number, the oscillatory blowing and suction flow control only has about 25% of the eectiveness of that observed in the experiment. The LES separation reattachment length is 10% longer than its experimental counterpart. Other flow quantities display favorable agreement with experimental data. Results demonstrate that both steady suction and oscillatory blowing and suction can be properly simulated by LES and eectively reduce the size of the separated flow region.