Merging Near-Wall RANS Models With LES for Separating and Reattaching Flows

Abstract

A method of coupling a low-Reynolds-number k–ε RANS (Reynolds-Averaged Navier-Stokes) model with Large-Eddy Simulation (LES) in a two-layer Hybrid LES/RANS (HLR) scheme is proposed in the present work. The RANS model covers the near-wall region and the LES model the remainder of the flow domain. Two different subgrid-scale (SGS) models in LES were considered, the Smagorinsky model and the one-equation model for the residual kinetic energy (Yoshizawa and Horiuti, 1985), combined with two versions of the RANS ε equation, one governing the “isotropic” (ε˜; Chien, 1982) and the other the “homogeneous” dissipation rate (εh; Jakirlic and Hanjalic, 2002). Both fixed and self-adjusting interface locations were considered. The exchange of the variables across the interface was adjusted by smoothing the turbulence viscosity either by adjusting the RANS model parameters, such as Cμ (Temmerman et al., 2005), or by applying an additional forcing at the interface using a method of digital-filter-based generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). The feasibility of the method was illustrated against the available DNS, fine- and coarse grid LES, DES (Detached Eddy Simulation) and experiments in turbulent flow over a backward-facing step at a low (Yoshioka et al., 2001) and a high Re number (Vogel and Eaton, 1985), periodic flow over a series of 2-D hills (Fro¨hlich et al., 2005) and in a high-Re flow over a 2-D, wall-mounted hump (Greenblat et al, 2004). Prior to these computations, the method was validated in a fully-developed channel flow at a moderate Reynolds number Rem ≈ 24000 (Abe et al., 2004).

Numerical and physical aspects in LES and hybrid LES/RANS of turbulent flow separation in a 3-D diffuser

“…Also, different sub-grid-scale (SGS) model formulations in LES (besides the Smagorinsky model the transport model for the residual kinetic energy from Yoshizawa and Horiuti (1985) has been tested) were combined with different eddy-viscosity-based RANS models. More details about the present HLR method are given in Jakirlić et al (2006 and Kniesner (2008).…”

Experimental and Computational Investigations of Flow and Mixing in a Single-Annular Combustor Configuration

“…The present HLR model has been thoroughly validated in configurations of different geometrical complexity featured by flow separation (from sharp-edged and continuous curved surfaces) and strong heating under the conditions of constant and variable fluid properties. Readers interested in more details about the present hybrid LES/RANS method are referred to Jakirlić et al [16], Kniesner et al [18] and Kniesner [19].…”

“…Presently a two-equation k − ε RANS model and the SGS model due to Smagorinsky were adopted, although the method could be easily extended to other eddy-viscosity-based RANS models as well as SGS models, see e.g. Jakirlić et al [16] and Kniesner [19]. …”

Wall Modeled Large Eddy Simulation of Flow Over a Wall-Mounted Hump

“…Table 3-2 Summary of previous work performed using other turbulence models Saric et al [8,36] assessed a number of computational models viz. LES, DES [4,37] , Delayed DES (DDES) [38] and a zonal hybrid LES/RANS [39] (HLR) scheme. They performed the solution of both 3D filtered and RANS equations on a block-structured body fitted collocated mesh, using a second order central scheme for spatial discretization and second order Crank Nicolson scheme for time advancement.…”