The State of the Art of Hybrid RANS/LES Modeling for the Simulation of Turbulent Flows

Abstract

This review presents the state of the art of hybrid RANS/LES modeling for the simulation of turbulent flows. After recalling the modeling used in RANS and LES methodologies, we propose in a first step a theoretical formalism developed in the spectral space that allows to unify the RANS and LES methods from a physical standpoint. In a second step, we discuss the principle of the hybrid RANS/LES methods capable of representing a RANS-type behavior in the vicinity of a solid boundary and an LES-type behavior far away from the wall boundary. Then, we analyze the principal hybrid RANS/LES methods usually used to perform numerical simulation of turbulent flows encountered in engineering applications. In particular, we investigate the very large eddy simulation (VLES), the detached eddy simulation (DES), the partially integrated transport modeling (PITM) method, the partially averaged Navier-Stokes (PANS) method, and the scale adaptive simulation (SAS) from a physical point of view. Finally, we establish the connection between these methods and more precisely, the link between PITM and PANS as well as DES and PITM showing that these methods that have been built by different ways, practical or theoretical manners have common points of comparison. It is the opinion of the author to consider that the most appropriate method for a particular application will depend on the expectations of the engineer and the computational resources the user is prepared to expend on the problem.

Computational Fluid Dynamic Simulation of Vertical Axis Hydrokinetic Turbines

“…Recently, hybrid unsteady RANS/LES method has been increasingly used for certain classes of simulations, including separated flows; nevertheless, the techniques that combine the near-wall RANS region with the outer, large-eddy simulation region need further development [51].…”

“…DES is a hybrid model of URANS and LES models, being the former one for modeling the wall region and the latter one for the other regions. The motivation of researchers for utilizing DES is the high cost of LES in the boundary layer region; the strategy of using DES aims at accurately modeling the large vortices in the separated shed wake while keeping the simulation of the near-wall region at a limited cost [51].…”

Towards a Predictive Hybrid RANS/LES Framework

“…With the target acceleration magnitude (6) and structure (9) in hand, additional modifications are necessary to respect RANS and DNS limits while also acknowledging the combination of h i and existing turbulent fluctuations would generally result in no net resolved production. The latter is addressed by testing the resolved production due to h i as…”

“…which will be used to clip (9). The RANS limit is readily apparent when α = 1 while identification of near-DNS conditions requires an approximation of the local Kolmogorov length scale.…”

“…It is widely recognized that combining Reynolds-averaged Navier-Stokes (RANS) models with large eddy simulation (LES) in a hybrid modeling framework can, in principle, provide a computationally tractable, predictive tool for simulation of high Reynolds number flows in complex geometries. Since the 1990s, many hybrid simulation approaches, including Detached Eddy Simulation (DES) and variants [1][2][3][4][5], partially-averaged Navier-Stokes [6,7], partially-integrated transport models [8,9], scale-adaptive simulation [10,11], zonal RANS/LES approaches [12,13], and others [14][15][16], have been developed. However, despite this research and the intuitive appeal of the ideas underlying hybrid models, because of a host of issues introduced by the blending of RANS and LES models as well as deficiencies inherited from the underlying models, a hybrid approach capable of reliably predicting a wide range of flows does not yet exist.…”