6,102 research outputs found

    A Nested-LES Approach for Computation of High-Reynolds Number, Equilibrium and Non-Equilibrium Turbulent Wall-Bounded Flows.

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    Computation of high Reynolds number, complex, non-equilibrium wall-bounded turbulent flows presents a major challenge for large-eddy simulation (LES), due to the stringent resolution requirements in the near-wall region in conventional LES, and the inability of existing wall models to accurately capture the near-wall dynamics in flows involving complex physics in the near-wall region. In this study, a novel nested-LES approach for computation of high Reynolds number, equilibrium and non-equilibrium, wall-bounded turbulent flows is proposed. The method couples well-resolved LES in a minimal flow unit with coarse-resolution LES in the full domain to provide high-fidelity simulations of the flow physics in both the inner and outer layers. The coupling between the two domains of nested-LES is achieved by dynamically renormalizing the velocity fields in each domain at each time-step during the course of the simulation to match the wall-normal profiles of the single-time ensemble-averaged kinetic energies of the components of mean and fluctuating velocities in both domains to those of the minimal flow unit in the inner layer, and to those of the full domain in the outer layer. The proposed nested-LES approach can be applied to any flows with at least one direction of local or global homogeneity, while reducing the required number of grid points from O(Re_t^2) of conventional LES to O(log{Re_t}) and O(Re_t^1) in flows with two or one directions of homogeneity, respectively. The proposed nested-LES approach has been applied to LES of equilibrium turbulent channel flow at Re_t ~= 1000 - 10000, and non-equilibrium, strained turbulent channel flow at Re_t ~=2000. In application to equilibrium turbulent channel flow, the nested-LES approach predicts the skin-friction coefficient, first-order turbulence statistics, higher-order moments, two-point correlations, correlation maps, and structural features of the flow in agreement with available direct numerical simulation (DNS) and experimental data. In application to non-equilibrium, strained turbulent channel flow, nested-LES predicts the evolution of skin-friction coefficients and one-point turbulence statistics in good agreement with experimental data in shear-driven, three-dimensional turbulent boundary-layer (TBL).PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120800/1/yifeng_1.pd

    Segregated Runge–Kutta time integration of convection-stabilized mixed finite element schemes for wall-unresolved LES of incompressible flows

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    In this work, we develop a high-performance numerical framework for the large eddy simulation (LES) of incompressible flows. The spatial discretization of the nonlinear system is carried out using mixed finite element (FE) schemes supplemented with symmetric projection stabilization of the convective term and a penalty term for the divergence constraint. These additional terms introduced at the discrete level have been proved to act as implicit LES models. In order to perform meaningful wall-unresolved simulations, we consider a weak imposition of the boundary conditions using a Nitsche’s-type scheme, where the tangential component penalty term is designed to act as a wall law. Next, segregated Runge–Kutta (SRK) schemes (recently proposed by the authors for laminar flow problems) are applied to the LES simulation of turbulent flows. By the introduction of a penalty term on the trace of the acceleration, these methods exhibit excellent stability properties for both implicit and explicit treatment of the convective terms. SRK schemes are excellent for large-scale simulations, since they reduce the computational cost of the linear system solves by splitting velocity and pressure computations at the time integration level, leading to two uncoupled systems. The pressure system is a Darcy-type problem that can easily be preconditioned using a traditional block-preconditioning scheme that only requires a Poisson solver. At the end, only coercive systems have to be solved, which can be effectively preconditioned by multilevel domain decomposition schemes, which are both optimal and scalable. The framework is applied to the Taylor–Green and turbulent channel flow benchmarks in order to prove the accuracy of the convection-stabilized mixed FEs as LES models and SRK time integrators. The scalability of the preconditioning techniques (in space only) has also been proven for one step of the SRK scheme for the Taylor–Green flow using uniform meshes. Moreover, a turbulent flow around a NACA profile is solved to show the applicability of the proposed algorithms for a realistic problem.Peer ReviewedPostprint (author's final draft
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