Large-eddy simulation of separated flows on unconventionally coarse grids
0
Citation
0
Reference
10
Related Paper
Abstract:
We examine and benchmark the emerging idea of applying the large-eddy simulation (LES) formalism to unconventionally coarse grids where RANS would be considered more appropriate at first glance. We distinguish this idea from very-large-eddy-simulation (VLES) and detached-eddy-simulation (DES), which require switching between RANS and LES formalism. LES on RANS grid is appealing because first, it requires minimal changes to a production code; second, it is more cost-effective than LES; third, it converges to LES; and most importantly, it accurately predicts flows with separation. This work quantifies the benefit of LES on RANS-like grids as compared to RANS on the same grids. Three canonical cases are considered: periodic hill, backward-facing step, and jet in cross flow. We conduct direct numerical simulation (DNS), proper LES on LES grids, LES on RANS-quality grids, and RANS. We show that while the LES solutions on the RANS-quality grids are not grid converged, they are twice as accurate as the RANS on the same grids.Keywords:
Large-Eddy Simulation
Detached-Eddy Simulation
Detached-Eddy Simulation
Reynolds stress
Large-Eddy Simulation
Turbulence Modeling
Solver
Cite
Citations (4)
Large-Eddy Simulation
Detached-Eddy Simulation
Cite
Citations (9)
The performance of an hybrid LES–RANS strategy, the Detached Eddy Simulation (DES), as a predictive tool for turbulent channel flow with massive separation is scrutinized. This is undertaken in a collaborative effort involving five different flow solvers used by five different groups to cover a broad range of numerical methods and implementations. This paper concentrates on DES results obtained with a computational mesh of approximately one million cells. The results are compared to those obtained by Large Eddy Simulations (LES) using the standard and the dynamic Smagorinsky models and an alternative hybrid LES–RANS – all computed on the same grid. Data of a highly resolved LES (roughly 13 million cells) are used for reference. Furthermore, the impact of resolution and, therefore, the location of the LES–RANS interface is studied.
Detached-Eddy Simulation
Large-Eddy Simulation
Cite
Citations (35)
Detached-Eddy Simulation
Large-Eddy Simulation
Cite
Citations (3)
This paper investigates the flow field and thermal characteristics in the near-field region of film cooling jets through numerical simulations using Reynolds-averaged Navier–Stokes (RANS) and hybrid unsteady RANS (URANS)/large eddy simulation (LES) models. Detailed simulations of flow and thermal fields of a single-row of film cooling cylindrical holes with 30 deg inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (FST) (10%). The realizable k‐ε model is used within the RANS framework and a realizable k‐ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Nevertheless, there still exist some discrepancies between numerical results and experimental data. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high FST is studied using the present DES results.
Large-Eddy Simulation
Detached-Eddy Simulation
Reynolds stress
Cite
Citations (24)
Large-Eddy Simulation
Detached-Eddy Simulation
Cite
Citations (3)
Detached-Eddy Simulation
Large-Eddy Simulation
Reynolds stress
Cite
Citations (118)
Following the idea of Speziale's Very Large Eddy Simulation(VLES) method,a new unified hybrid simulation approach was proposed which can change seamlessly from RANS(Reynolds-Averaged Navier-Stokes) to LES(Large Eddy Simulation) method depending on the numerical resolution.The model constants were calibrated in accordance with other hybrid methods.Besides being able to approach the two limits of RANS and LES,the new model also provides a proper VLES mode between the two limits,and thus can be used for a wide range of mesh resolutions.Also RANS simulation can be recovered near the wall which is similar to the Detached Eddy Simulation(DES) concept.This new methodology was implemented into Wilcox's k-ω model and applications were conducted for fully developed turbulent channel flow at Reτ = 395 and turbulent flow past a square cylinder at Re = 22000.Results were compared with LES predictions and other studies.The new method is found to be quite efficient in resolving large flow structures,and can predict satisfactory results on relative coarse mesh.
Large-Eddy Simulation
Detached-Eddy Simulation
Cite
Citations (0)
This paper presents numerical simulations for the prediction of the flow around the Ahmed body, with the 25 • and 35 • slant angles, obtained with the flow solver ISIS-CFD. Two RANS (Reynolds Averaged Navier-Stokes) turbulence models, as the k − ω SST and the EARSM (Explicit Algebraic Stress Model) and two hybrid RANS-LES models, as DES (De-tached Eddy Simulation) and IDDES (Improved Delay Detached Eddy Simulation) models, are used. The use of a hybrid RANS-LES model, and more particularly the IDDES model, offers an advantage over RANS models in term of the force coefficients, and general flow field.
Detached-Eddy Simulation
Large-Eddy Simulation
Reynolds stress
Turbulence Modeling
Solver
Cite
Citations (2)
In the present article, we introduce a local hybrid RANS/LES turbulence model, the Flow-based Stress-Blended Eddy Simulation (Fb-SBES). The methodology is applied to urban flow simulations in atmospheric boundary layer. The blending from RANS to LES is performed on the fly with respect to a flow deviation parameter. This makes the model self-adaptive and requires no prior knowledge of the flow contrary to typical zonal LES models. The present methodology enables the RANS equations to be solved in the major part of the computational domain (e.g on average 88% for a single building). The RANS zone is modelled with a comprehensive RANS turbulence model for ABL simulations that sustains the fully developed inlet conditions until the built environment. In general, Fb-SBES shows better agreement with experimental data on the building and in the wake compared to advanced RANS and DDES simulations.
Large-Eddy Simulation
Detached-Eddy Simulation
Turbulence Modeling
Cite
Citations (10)