scholarly journals Estimating the Reattachment Length by Realizing a Comparison between URANS k-Omega SST and LES WALE Models on a Symmetric Geometry

Symmetry ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1555
Author(s):  
Daniel Teso-Fz-Betoño ◽  
Martin Juica ◽  
Koldo Portal-Porras ◽  
Unai Fernandez-Gamiz ◽  
Ekaitz Zulueta
Keyword(s):  
Eddy Viscosity ◽  
Mechanical Energy ◽  
Expansion Ratio ◽  
Navier Stokes ◽  
Scale Analysis ◽  
Reattachment Length ◽  
Reattachment Point ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Symmetric Geometry

In this study, a water reattachment length was calculated by adopting two different models. The first was based on Unsteady Reynolds-Averaged Navier–Stokes (URANS) k-omega with Shear Stress Transport (SST); the second was a Large Eddy Simulation (LES) with Wall-Adapting Local Eddy-Viscosity (WALE). Both models used the same mesh and were checked with Taylor length-scale analysis. After the analysis, the mesh had 11,040,000 hexahedral cells. The geometry was a symmetrical expansion–contraction tube with a 4.28 expansion ratio that created mechanical energy losses, which were taken into account. Moreover, the reattachment length was estimated by analyzing the speed values; the change of speed value from negative to positive was used as the criterion to recognize the reattachment point.

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Tom Hickling ◽  
Li He
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Systematic Investigation ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Detached Eddy Simulation ◽  
Bulk Fluid ◽  
Eddy Simulation ◽  
Rotating Cavity ◽  
Large Eddy

Abstract Across the open literature, there is no clear consensus on what the most suitable modeling fidelity is for rotating cavity flows. Although it is a widely held opinion that unsteady Reynolds-averaged-Navier–Stokes (URANS) approaches are unsuitable, many authors have succeeded in getting reasonable heat transfer results with them. There is also a lack of research into the validity of hybrid URANS/large eddy simulation (LES) type approaches such as detached eddy simulation (DES). This paper addresses these research challenges with a systematic investigation of a rotating cavity with axial throughflow at Grashof numbers of 3.03×109 and 3.03×1011. The disk near-wall layers remained laminar at both conditions, meaning that a turbulence model should not be active in these regions. The disk heat transfer was observed to affect the near-disk aerodynamics, which in turn affect the disk heat transfer: this feedback loop implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, additional eddy viscosity in URANS and DES was found to interfere with the formation of heat transfer enhancing streaks, whilst these were always captured by LES. DES exhibited a concerning behavior at the higher Grashof number. Locally generated eddy viscosity from the shroud was injected into the bulk fluid by the radial inflow. This contaminated the entire cavity with nonphysical modeled turbulence. As the radial inflow is a characteristic feature of rotating cavity flows, these results show that caution is necessary when applying hybrid URANS/LES approaches to this type of flow.

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Hayder Schneider ◽  
Dominic von Terzi ◽  
Hans-Jörg Bauer ◽  
Wolfgang Rodi
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Expansion Ratio ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reasonable Accuracy ◽  
Wall Functions ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

Large-eddy simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) calculations of the flow in two asymmetric three-dimensional diffusers were performed. The setup was chosen to match an existing experiment with separation. Both diffusers possess the same expansion ratio but differ in performance. The aim of the present study is to find the least expensive method to reliably and with reasonable accuracy account for the impact of the change in geometry. RANS calculations failed to predict both the extent and location of the separation. In contrast, LES with wall-functions delivered results within the accuracy of the experimental data.

Evaluation of PANS Methodology With Nonlinear Eddy Viscosity Closure: Flow Past a Heated Sphere

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Sagar Saroha ◽  
Krishnendu Chakraborty ◽  
Sawan S. Sinha ◽  
Sunil Lakshmipathy
Keyword(s):  
Eddy Viscosity ◽  
Thermal Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow Past ◽  
Large Eddy ◽  
Reynolds Averaging ◽  
Better Than ◽  
Flow Past A Sphere

Abstract The partially averaged Navier–Stokes (PANS) approach has emerged as a viable scale-resolving bridging method over the last decade. Conventional PANS method, based on the linear eddy viscosity closure, overcomes the scale-resolving inadequacies of Reynolds-averaging but still suffers from limitations arising from linear constitutive modeling of turbulent stresses. Linear PANS has been evaluated in a variety of complex flow fields, including the benchmark case of flow around a sphere. In this work, the authors assess the potential of nonlinear eddy viscosity closure and further extend the evaluation of nonlinear closure in predicting thermal characteristics (besides hydrodynamics) of flow past a sphere. The presented evaluation has been performed on the basis of various surface-related and wake-related quantities. Our results are compared against available experimental and direct numerical simulation (DNS)/large eddy simulation studies. Our study shows that for the same value of the filter-control parameters, nonlinear PANS performs significantly better than linear PANS.

A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

2004 ◽  
Author(s):  
Sanjin Sˇaric´ ◽  
Suad Jakirlic´ ◽  
Cameron Tropea
Keyword(s):  
Navier Stokes ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Inlet Channel ◽  
Flow Separation Control ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Sst Model ◽  
Perturbation Frequency ◽  
Length Reduction

Turbulent flow over a backward-facing step perturbed periodically by an alternating blowing/suction through a thin slit situated at the step edge was studied computationally using the LES (Large Eddy Simulation), DES (Dettached Eddy Simulation) and T-RANS (Transient Reynolds-Averaged Navier-Stokes) techniques. The flow configuration considered (ReH = UcH/ν = 3700) has been investigated experimentally by Yoshioka et al. (2001). The periodical blowing/suction with zero mass flux is governed by a sinusoidal law: ve = 0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St = 0.08, 0.19 and 0.30 were investigated (St = feH/Uc). The experimental observation, that the perturbation frequency St = 0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods applied. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with the LES (24.5%) and DES (35%) methods whereas the T-RANS computations show a weak sensitivity to the perturbation: 5.9% when using the Spalart-Allmaras model and 12.9% using the k–ω SST model.

Towards Large-Eddy Simulation of Turbulent Flow in a Centrifugal Impeller

2011 ◽  
Author(s):  
Gorazd Medic ◽  
Jinzhang Feng ◽  
Liwei Chen ◽  
Om Sharma
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Scale Model ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy

Large-eddy simulation (LES) using wall-adapting local eddy-viscosity (WALE) subgrid scale model has been applied towards elucidating the complex turbulent flow physics in a centrifugal impeller. Several canonical cases of increased complexity were analyzed to better understand the advantages and challenges of applying the LES framework to the aforementioned target problem. These include turbulent flow in a rotating channel, a straight and a curved duct. Results obtained with LES are compared in detail with two-equation eddy-viscosity Reynolds Averaged Navier-Stokes (RANS) turbulence models widely used in industry, as well as, for some of the canonical cases, with hybrid RANS/LES approaches such as the detached eddy simulation (DES) and scale-adaptive simulation (SAS). Finally, LES has been applied to turbulent flow in NASA CC3 centrifugal impeller with grids of increased resolution (up to 100 million computational cells per passage).

scholarly journals Performance of turbulence and cavitation models in prediction of incipient and developed cavitation

2016 ◽  
Vol 18 (4) ◽  
pp. 333-350 ◽  
Author(s):  
Phoevos Koukouvinis ◽  
Homa Naseri ◽  
Manolis Gavaises
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Model ◽  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Navier Stokes ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
The Impact

The aim of this article is to assess the impact of turbulence and cavitation models on the prediction of diesel injector nozzle flow. Two nozzles are examined, an enlarged one, operating at incipient cavitation, and an industrial injector tip, operating at developed cavitation. The turbulence model employed includes the re-normalization group k–ε, realizable k–ε and k–ω shear stress transport Reynolds-averaged Navier–Stokes models; linear pressure–strain Reynolds stress model and the wall adapting local eddy viscosity large eddy simulation model. The results indicate that all Reynolds-averaged Navier–Stokes and the Reynolds stress turbulence models have failed to predict cavitation inception due to their limitation to resolve adequately the low pressure existing inside vortex cores, which is responsible for cavitation development in this particular flow configuration. Moreover, Reynolds-averaged Navier–Stokes models failed to predict unsteady cavitation phenomena in the industrial injector. However, the wall adapting local eddy viscosity large eddy simulation model was able to predict incipient and developed cavitation, while also capturing the shear layer instability, vortex shedding and cavitating vortex formation. Furthermore, the performance of two cavitation methodologies is discussed within the large eddy simulation framework. In particular, a barotropic model and a mixture model based on the asymptotic Rayleigh–Plesset equation of bubble dynamics have been tested. The results indicate that although the solved equations and phase change formulation are different in these models, the predicted cavitation and flow field were very similar at incipient cavitation conditions. At developed cavitation conditions, standard cavitation models may predict unrealistically high liquid tension, so modifications may be essential. It is also concluded that accurate turbulence representation is crucial for cavitation in nozzle flows.

NUMERICAL STUDY OF DETONATION PROPAGATION IN VISCOUS TURBULENT FLOW IN A DUCT

2020 ◽  
Author(s):  
V. A. SABELNIKOV ◽  
◽  
V. V. VLASENKO ◽  
S. BAKHNE ◽  
S. S. MOLEV ◽  
...  
Keyword(s):  
Complex Geometry ◽  
Numerical Study ◽  
Navier Stokes ◽  
Detonation Waves ◽  
Detonation Propagation ◽  
Eddy Simulation ◽  
Detonation Structure ◽  
Classical Studies ◽  
Large Eddy ◽  
Physical Effects

Gasdynamics of detonation waves was widely studied within last hundred years - analytically, experimentally, and numerically. The majority of classical studies of the XX century were concentrated on inviscid aspects of detonation structure and propagation. There was a widespread opinion that detonation is such a fast phenomenon that viscous e¨ects should have insigni¦cant in§uence on its propagation. When the era of calculations based on the Reynolds-averaged Navier- Stokes (RANS) and large eddy simulation approaches came into effect, researchers pounced on practical problems with complex geometry and with the interaction of many physical effects. There is only a limited number of works studying the in§uence of viscosity on detonation propagation in supersonic §ows in ducts (i. e., in the presence of boundary layers).

scholarly journals Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil

2021 ◽  
Vol 9 (7) ◽  
pp. 742
Author(s):  
Minsheng Zhao ◽  
Decheng Wan ◽  
Yangyang Gao
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Specific Information ◽  
Cloud Cavitation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Shedding Frequency ◽  
Reynolds Average

The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.

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