Wall-Modeled Large Eddy Simulation and Detached Eddy Simulation of Wall-Mounted Separated Flow via OpenFOAM

Abstract

Considering grid requirements of high Reynolds flow, wall-modeled large eddy simulation (WMLES) and detached eddy simulation (DES) have become the main methods to deal with near-wall turbulence. However, the flow separation phenomenon is a challenge. Three typical separated flows, including flow over a cylinder at ReD = 3900 based on the cylinder diameter, flow over a wall-mounted hump at Rec = 9.36e5 based on the hump length, and transonic flow over an axisymmetric bump with shock-induced separation at Rec = 2.763e6 based on the bump length, are used to verify WMLES, shear stress transport k-ω DES (SST-DES), and Spalart–Allmaras DES (SA-DES) methods in OpenFOAM. The three flows are increasingly challenging, namely laminar boundary layer separation, turbulent boundary layer separation, and turbulent boundary layer separation under shock interference. The results show that WMLES, SST-DES, and SA-DES methods in OpenFOAM can easily predict the separation position and wake characteristics in the flow around the cylinder, but they rely on the grid scale and turbulent inflow to accurately simulate the latter two flows. The grid requirements of Larsson et al. (δ/Δx,δ/Δy,δ/Δz≈(12,50,20)) are the basis for simulating turbulent boundary layers upstream of flow separation. A finer mesh (δ/Δx,δ/Δy,δ/Δz≈(40,75,40)) is required to accurately predict the separation and reattachment. The WMLES method is more sensitive to grid scales than the SA-DES method and fails to obtain flow separation under a coarser grid, while SST-DES method can only describe the vortices generated by the separating shear layer, but not within the turbulent boundary layer, and overestimates the separation-reattachment zone based on the grid system in this paper.

Continuous Eddy Simulation (CES) of Transonic Shock-Induced Flow Separation

“…In contrast, the CES-KOS model provides the highest accuracy regarding the estimation of the separation length, with an error of only ≈4%. Figure 19 shows in its first row streamwise velocity profiles obtained by CES-KOS, WMLES [41], and WRLES [42]. It may be seen that the CES-KOS model predicts the streamwise velocity more accurately than WMLES and WRLES.…”

“…Using an axisymmetric grid, we simulate in this way a slice of the 3D axisymmetric bump geometry (a spanwise-periodic configuration with the same cross-sectional profile as given by the three-dimensional bump geometry). The same approach was applied by Ren et al [41] as well as Elnahhas et al [46]. Characteristic boundary conditions were imposed at the freestream and outflow boundaries.…”

“…The inadequacy of RANS to accurately represent unsteady flow characteristics resulted in the development of DES methods. In this subsection, we will compare CES-KOS predictions with three DES methods: the Wray-Agarwal detached eddy simulation (WA-DES) method [50], the Spalart-Allmaras-based DES (SA-DES) [41] method, and the zonal improved delayed DES (IDDES) [34] method. The zonal IDDES technique uses a synthetic turbulence generator at an adaptive RANS-LES interface located at x/c = −0.5 (0.5c upstream of the bump).…”

“…Figure 19. CES-KOS vs. LES-type WRLES [42] and WMLES [41] models: Profiles of the normalized streamwise velocity ⟨U⟩/U re f , Reynolds stress ⟨uv⟩/U 2 re f , pressure, and skin-friction coefficients at different locations.…”

Image Processing and CFD Simulation Method Comparison in Determining and Visualizing Fluid Flow of a Marine UAV

“…for LES are obtained by spatial filtering of the incompressible Navier-Stokes equations, where[13]: simulation was conducted on a budget gaming computer with specifications which can be mentioned as follows, Processor : AMD Ryzen 7 3750H with Radeon Vega Mobile Gfx (8 CPUs) ~ 2…”