Abstract
The intent of shielding functions in delayed detached-eddy simulation methods (DDES) is to preserve the wall boundary layers as Reynolds-averaged Navier–Strokes (RANS) mode, avoiding possible modeled stress depletion (MSD) or even unphysical separation due to grid refinement. An entropy function fs is introduced to construct a DDES formulation for the k-ω shear stress transport (SST) model, whose performance is extensively examined on a range of attached and separated flows (flat-plate flow, circular cylinder flow, and supersonic cavity-ramp flow). Two more forms of shielding functions are also included for comparison: one that uses the blending function F2 of SST, the other which adopts the recalibrated shielding function fd_cor of the DDES version based on the Spalart-Allmaras (SA) model. In general, all of the shielding functions do not impair the vortex in fully separated flows. However, for flows including attached boundary layer, both F2 and the recalibrated fd_cor are found to be too conservative to resolve the unsteady flow content. On the other side, fs is proposed on the theory of energy dissipation and independent on from any particular turbulence model, showing the generic priority by properly balancing the need of reserving the RANS modeled regions for wall boundary layers and generating the unsteady turbulent structures in detached areas.
Highlights
Detached-eddy simulation (DES) takes advantage of the Reynolds-averaged Navier–Strokes (RANS) method where mean flow is attached and steady, while offering, like large-eddy simulation (LES), the sensitivity to capture unsteady flow phenomena in areas of physical interest such as wakes or recirculation zones [1,2,3,4,5]
The transition from RANS to LES mode would be located within the boundary layer, if the mesh is refined with grid spacing is much smaller than the boundary-layer thickness
Similar to the procedure adopted by Reference [7], we present three types of grids with different mesh resolutions in order to evaluate the grid sensitivity present threeDDES
Summary
Detached-eddy simulation (DES) takes advantage of the Reynolds-averaged Navier–Strokes (RANS) method where mean flow is attached and steady (e.g., walls), while offering, like large-eddy simulation (LES), the sensitivity to capture unsteady flow phenomena in areas of physical interest such as wakes or recirculation zones [1,2,3,4,5]. This strategy is beyond the computational cost of a steady RANS calculation, it reveals nearly as much information about the flow dynamics as LES. Menter and Kuntz [8] used the blending function F2 of the k-ω shear stress transport (SST) model [9] to “shield” the boundary layer, by which they implied “preserve RANS mode”, or “delay LES function” in
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