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DES of Turbulent Flow Over Wall-Mounted Obstacles Using Wall Functions
백중철,Fotis Sotiropoulos 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.2
An adaptive wall function is employed in Detached-Eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS) -Large Eddy Simulation (LES) model, of turbulent flow past two wall-mounted cubic obstacles in tandem at a Reynolds number Re =22,000 based on the bulk velocity and the obstacle height. Numerical results are compared with previously published DES solutions obtained on wall integration grids and the experimental measurements of Martinuzzi and Havel (2000). The result shows that wallfunction approach in DES allows reasonable reproduction of coherent vortical structures massively separated from the wall-mounted obstacles to be achieved on wall function grids which require just the half of grid nodes of wall resolving grids. The numerical solutions computed by wall function computations reveal energetic unsteady flow fields with complex coherent vortical structures separated from obstacle edges, whose accuracy is better than those obtained by the unsteady RANS computations on the wall integration grid. Wall function solutions appear to be comparable to the wall-resolving DES solutions in most regions except at the junction of obstacle and the bottom wall where the flow is dominated by the horseshoe vortex with intense unsteadiness. The result confirms that DES with wall function approximation can reasonably resolves geometry-induced unsteady three-dimensional turbulent motions.
Kang, Seokkoo,Sotiropoulos, Fotis American Society of Civil Engineers 2015 Journal of hydraulic engineering Vol.141 No.10
<P> Large-eddy simulation (LES) of a three-dimensional, turbulent free surface flow past a stream restoration structure with arbitrarily complex geometries is presented. The three-dimensional, incompressible, spatially filtered Navier-Stokes and continuity equations are solved in generalized curvilinear coordinates. For the solution of mixed air-water flows, the curvilinear immersed boundary (CURVIB)-level set method developed previously is used and extended to carry out LES. Complex solid geometries are handled by the sharp-interface CURVIB method, and the subgrid scale stress terms arising from the spatial filtering of the Navier-Stokes equations are closed by the dynamic Smagorinsky model. To demonstrate the potential of the CURVIB-LES-level set model for simulating real-life, turbulent free surface flows involving arbitrarily complex geometries, LES is carried out for the flow past a complex rock structure that is fully submerged in water in a laboratory flume. The simulations show that the method is able to predict the time-averaged value as well as the root-mean-square fluctuations of water surfaces with good accuracy. Moreover, it is seen that the free surface flow at a high Froude number causes a significant level of fluctuations of water surface elevation and velocity at the water surface. </P>
DES of Turbulent Flow Over Wall-Mounted Obstacles Using Wall Functions
Paik, Joongcheol,Sotiropoulos, Fotis 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.2
An adaptive wall function is employed in Detached-Eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS) - Large Eddy Simulation (LES) model, of turbulent flow past two wall-mounted cubic obstacles in tandem at a Reynolds number Re = 22,000 based on the bulk velocity and the obstacle height. Numerical results are compared with previously published DES solutions obtained on wall integration grids and the experimental measurements of Martinuzzi and Havel (2000). The result shows that wall-function approach in DES allows reasonable reproduction of coherent vortical structures massively separated from the wall-mounted obstacles to be achieved on wall function grids which require just the half of grid nodes of wall resolving grids. The numerical solutions computed by wall function computations reveal energetic unsteady flow fields with complex coherent vortical structures separated from obstacle edges, whose accuracy is better than those obtained by the unsteady RANS computations on the wall integration grid. Wall function solutions appear to be comparable to the wall-resolving DES solutions in most regions except at the junction of obstacle and the bottom wall where the flow is dominated by the horseshoe vortex with intense unsteadiness. The result confirms that DES with wall function approximation can reasonably resolves geometry-induced unsteady three-dimensional turbulent motions.
Numerical study of flow dynamics around a stream restoration structure in a meandering channel
KANG, SEOKKOO,SOTIROPOULOS, FOTIS International Association for Hydraulic Research 2015 Journal of hydraulic research Vol.53 No.2
<P> In this paper the flow around a streambank-attached in-stream structure - rock vane - installed in a meandering channel is investigated via large-eddy simulation (LES). LES is carried out for the case where the rock vane is installed along the outer bank of a field-scale, natural-like experimental meandering channel facility. Analysis of the simulated flow field shows that the rock vane acts to displace the upstream high-velocity core toward the channel centre and it effectively reduces the bed shear stress along the outer streambank. It is also found that the presence of the rock vane gives rise to the growth of the secondary flow cell formed along the outer streambank, which is often called the outer bank cell. Numerical results suggest that the growth of the outer bank cell and the subsequent displacement of the outer bank shear layer are responsible for the displacement of channel thalweg toward the channel centre. </P>