Title: “Near-Wall Treatments for Coarse Grid Large-Eddy Simulation" Speaker: Jeremy Templeton, Interview Candidate, Stanford University, Stanford, California Date/Time: Wednesday, April 20, 2005, 11:00-12:15 am (MT) Location: Building 980, Room 95 (Sandia, NM), Building 915, Room S101 (Sandia, CA) Brief Abstract: The major bottleneck preventing large-eddy simulations (LES) of turbulent fluid flow from being used in the complex geometries and high Reynolds numbers typically encountered in engineering practice is the need to resolve the near-wall layer. This is because current sub-grid scale (SGS) models cannot accurately account for the highly energetic and anisotropic small scales found in this region. To avoid the cost of resolving these scales, wall treatments have been used in LES to allow it to accurately capture the important physics of the flow without resolving the near-wall turbulence. In this work, optimal control theory has been used to derive a technique that provides boundary conditions for LES so that it can be used on coarse grids that do not resolve the wall region. The controller is able to compensate not only for the unresolved physics but also for the numerical and SGS modeling errors that occur when coarse grids are used. Results from high Reynolds number plane channel flow have demonstrated that this approach can accurately reproduce the theoretical mean velocity profile for this configuration. Higher order statistics have shown that the rms profiles are also well predicted in the outer flow, but near the wall are elevated in order to compensate for SGS model deficiencies. To improve the prediction of these higher order quantities, a new technique for augmenting LES SGS models by correcting them based on the resolved turbulence is currently being pursued. Preliminary results have indicated that this method has the potential to accurately predict both mean and rms profiles, and has the additional advantages of being computationally inexpensive and easy to implement. CSRI POC: Patty Hough (925) 294-1518/Monica Martinez-Canales, (925) 294-3157 |