Towards Optimal Large-Eddy Simulation of Wall-Bounded Flows

141 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.The issue of modeling the instantaneous viscous and pressure stresses at the wall is addressed via a review of the OLES simulation of turbulent channel flow performed by Das (2004). In this approach, a buffer region with zero velocity is attached adjacent to the wall, and the extended velocity field is filtered using a Fourier-cutoff filter in all directions. The instantaneous wall stresses are then obtained using a "no leakage" condition, where the energy in the buffer-region is minimized at every time-step. Some changes are introduced to the previous formulation---the nonlinear and subgrid terms in the LES equation are obtained using a nonlocal re-filtering approach and a "matched buffer" condition is used to obtain the wall stresses. Simulations performed using both the "no leakage" and "matched buffer" conditions yield statistics which compare well with DNS data. Some numerical experiments involving the linear OLES kernel are also performed, where it is shown that the positive eigenvalues in the kernel and the skew-symmetric part of the kernel are important.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD