Large eddy simulation coupled with immersed boundary method for turbulent flows over a backward facing step

2020 ◽  
pp. 095440622095489
Author(s):  
Dandan Yang ◽  
Sida He ◽  
Lian Shen ◽  
Xianwu Luo
Keyword(s):  
Large Eddy Simulation ◽  
Flow Separation ◽  
Reverse Flow ◽  
Immersed Boundary ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ib Method

In the present work, large eddy simulation coupled with immersed boundary (LES-IB) method is applied to simulate a backward facing step (BFS) flow, which is a canonical fluid dynamics problem involving flow separation, recirculation and reattachment that are common in many practical applications. The computed reattachment length, a primary parameter to evaluate the overall performance of the numerical method, shows promising accuracy in the present work compared to the alternative numerical simulations. Based on the mean velocity profiles at four representative locations, there is fairly well quantitative agreement among the present LES-IB, DNS and the experiment. The results reveal that the reverse flow in the reattachment region leads to little over-prediction of the reattachment length compared to the DNS result. Furthermore, second-order statistics are in good agreement with the reference data in spite of discrepancies in the recirculation and reattachment region owing to complex flow structure, verifying the accuracy of the present method. In addition, the instantaneous flow fields are also analyzed to show the capability of the present LES-IB method in vortex-capture, and one may see the transient process of flow separation based on the analysis of Lagrangian coherent structure (LCS).

Turbulence Modeling Using Z-F, RSM, LES and WMLES for Flow Analysis in Z-Shape Ducts

2020 ◽  
Author(s):  
Mohammed Karbon ◽  
Ahmad K. Sleiti
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Large Eddy Simulation ◽  
Flow Separation ◽  
Temporal Variations ◽  
Mean Flow ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rsm Model

Abstract Turbulent flow in Z-shape duct configuration is investigated and analyzed using Reynolds Stress Model (RSM), Large Eddy Simulation (LES), ζ-f Model, and Wall-Modeled Large Eddy Simulation (WMLES). The results are validated and compared to experimental data. Both RSM and ζ-f models are based on steady-state RANS solutions, while LES and WMLES models account for temporal variations transient behavior of the flow turbulence. The focus was on regions where RSM has over or under predicted the flow and regions where there are flow separations and high turbulence. LES simulation results have shown under-prediction and over-prediction in the flow separation and re-attachment regions. It is found that the turbulent kinetic energy production in ζ equation is much easier to reproduce accurately than other models. Both mean velocity gradient and local turbulent stress terms are also much easier to resolve properly. The current research has found that ζ-f model not only takes less time to complete the simulation but also the mean flow velocity profile results are in better agreement with experimental data than RSM model despite both are coupled steady-state RANS. ζ-f model numerically resolved both the flow separation and re-attachment regions better than RSM model. WMLES model is employed to investigate the SGS model impact on the small eddies dissipated from the large eddies. Such WMLES model produces much better results than the LES model, however the SGS viscosity damps the energy of the flow.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Large Eddy Simulation of the Vortex End in Reverse-Flow Centrifugal Separators

2009 ◽  
Author(s):  
Gleb I. Pisarev ◽  
Alex C. Hoffmann ◽  
Weiming Peng ◽  
Henk A. Dijkstra ◽  
Theodore E. Simos ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Reverse Flow ◽  
Eddy Simulation ◽  
Large Eddy

Kinetic-energy-flux-constrained model using an artificial neural network for large-eddy simulation of compressible wall-bounded turbulence

2021 ◽  
Vol 932 ◽  
Author(s):  
Changping Yu ◽  
Zelong Yuan ◽  
Han Qi ◽  
Jianchun Wang ◽  
Xinliang Li ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Energy Flux ◽  
Mean Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Bounded Turbulence

Kinetic energy flux (KEF) is an important physical quantity that characterizes cascades of kinetic energy in turbulent flows. In large-eddy simulation (LES), it is crucial for the subgrid-scale (SGS) model to accurately predict the KEF in turbulence. In this paper, we propose a new eddy-viscosity SGS model constrained by the properly modelled KEF for LES of compressible wall-bounded turbulence. The new methodology has the advantages of both accurate prediction of the KEF and strong numerical stability in LES. We can obtain an approximate KEF by the tensor-diffusivity model, which has a high correlation with the real value. Then, using the artificial neural network method, the local ratios between the real KEF and the approximate KEF are accurately modelled. Consequently, the SGS model can be improved by the product of that ratio and the approximate KEF. In LES of compressible turbulent channel flow, the new model can accurately predict mean velocity profile, turbulence intensities, Reynolds stress, temperature–velocity correlation, etc. Additionally, for the case of a compressible flat-plate boundary layer, the new model can accurately predict some key quantities, including the onset of transitions and transition peaks, the skin-friction coefficient, the mean velocity in the turbulence region, etc., and it can also predict the energy backscatters in turbulence. Furthermore, the proposed model also shows more advantages for coarser grids.

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