WALE Model Research Articles

Development of Wall-Adapting Local Eddy Viscosity Model for Study of Fire Dynamics in a Large Compartment

The Wall Adpating Local Eddy Viscosity (WALE) subgrid-scale turbulence model was adopted for an in-house large eddy simulation (LES) fire code in which the turbulence is fully coupled combustion and radiation models. The traditional Smagorinsky subgrid-scale model accounts only strain rate of the turbulent structure while the WALE model considers both the strain and the rotation rates. Furthermore, the WALE model automatically recovers the near wall-scaling for the eddy viscosity hence more adaptive for wall bounded flows.A 15 m long test hall fire was reconstructed by the in-house fire code with 1.5 MW fire source. The performance of the WALE model was assessed by comparingpredicted transient gas temperatures and velocities at various spatial locations.

Effect of Turbulence Model on Simulation of Vehicle Aerodynamic Characteristics Based on XFlow

The stability, comfort and safety of vehicles depend largely on the aerodynamic characteristics of the vehicle in high speed. As the turbulence model plays a decisive factor in the numerical simulation of aerodynamic characteristics, a simulation analysis of Ahmed model with a slant angle of is carried out by the XFlow software. Then the paper presents the changes of aerodynamic parameters relative to the experimental values with four turbulence models: Spalart-Allmaras model, WALE model, Dynamic Smagorinsky model and Smagorinsky model. It is found that the result of simulation with Smagorinsky model is in good agreement with experimental value, and the simulation of the wake vortex separation is consistent with the actual phenomenon. The Smagorinsky turbulence model has a good simulation precision.

Large Eddy Simulation for an inherent boron dilution transient

The present paper focuses on the validation and applicability of large eddy simulation (LES) to analyze the transport and mixing in the reactor pressure vessel (RPV) during an inherent boron dilution transient (BDT) scenario. Extensive validation data comes from relevant integral tests performed in the scaled ROCOM experimental facility. The modeling of sub-grid-scales is based on the WALE model. A fully conformal polyhedral grid of about 15 million cells is constructed to capture all details in the domain, including the complex structures of the lower-plenum. Detailed qualitative and quantitative validations are performed by following a systematic multi-step validation methodology. Qualitative comparisons to the experimental data in the cold legs, downcomer and the core inlet showed good predictions by the LES model. Minor deviations seen in the quantitative comparisons are rigorously quantified. A key parameter which is affecting the core neutron kinetics response is the value of highest deborated slug concentration that occurs at the core inlet during the transient. Detailed analyses are made at the core inlet to evaluate not only the value of the maximum slug concentration, but also the location and the time at which it occurs during the transient. The relative differences between the ensemble averaged experimental data and CFD predictions were within the range of relative differences seen within 10 different experimental realizations. For the studied scenario, the present LES results lend support to its reliability in consistently predicting the slug transport in the RPV.

Numerical modelling of odour dispersion around a cubical obstacle using large eddy simulation

In the present work two different large eddy simulation (LES) approaches, namely the Dynamic Smagorinsky model and the Wale model, are used to simulate the air flow and pollutant dispersion around a cubical obstacle. Results are compared with wind tunnel data (WT) and with results from the Smagorinsky LES model. Overall agreement was good between the different LES approaches and the WT results, both for the mean and fluctuating flow and concentration patterns. LES models can provide good estimates of concentration fluctuation intensity and enable the calculation of the intermittency factor. The model results indicate that LES is a viable tool for odour impact assessment.

A relative assessment of sub grid scale models for large eddy simulation of co-axial combustor

Large eddy simulation (LES) of a co-axial combustor is reported. Accuracy of LES depends on the ability of the sub-grid scale (SGS) models to predict the turbulent viscosity. The sensitivity of LES results for different SGS models is established for a coaxial annular combustor. The radial, axial and tangential velocity distribution predicted by four sub-grid scale models is compared with the experimental results of Sommerfeld and Qiu. It is observed that the flow physics is captured more accurately by WALE model as compared to other SGS models. The predictions of WALE model are closer to the experimental results for all stations in the flow domain.

A finite element LES for high- Re flow in a short-elbow pipe with undisturbed inlet velocity

The paper is concerned with a large-eddy simulation (LES) for a high-Reynolds-number flow in a short-elbow pipe, which can potentially be employed in the primary piping system of the Japan Sodium-cooled Fast Reactor (JSFR). The basic performance of the LES is studied for an elbow pipe flow without turbulence at inlet boundary at Re = 1.2 × 10 6 by comparison with a flow observed in a 1/3-scale water experiment, where the flow disturbance at the pipe inlet is small. In setting up the computational conditions, special care was taken to ensure that the mesh subdivision was suitable for the simulation of the pipe flow through a theoretical consideration. We discuss the effects of the turbulence model (Smagorinsky model, WALE model) and the inlet velocity profile on the results. The mechanism of the pressure fluctuation and the origin of the fluid force are also discussed with the aid of spectral analysis and the visualization of essential hydraulic quantities.

Investigation of the LES WALE turbulence model within the lattice Boltzmann framework

Turbulence models which can perform the transition from laminar flow to fully developed turbulent flow are of key importance in industrial applications. A promising approach is the LES WALE model, which can be used without wall functions or global damping functions. The model produces an efficient and fast scheme due to its algebraic character. Additionally, its prediction of the transition from laminar to turbulent regimes has shown promising results. In this work, the LES WALE model is investigated within the lattice Boltzmann framework. For validation purposes, various test cases are presented. First, a channel flow at a Reynolds number of 6876 is investigated. Secondly, the flow around a wall-mounted cube at various Reynolds numbers is determined. The flow regime varies from laminar, to transitional, to fully turbulent conditions at a Reynolds number of 40,000 with respect to the cube height.

Large-eddy simulation of an impinging jet in a cross-flow on a heated wall-mounted cube

A large-eddy simulation (LES) is performed in order to predict the mean velocity field, the turbulence characteristics and the heat transfer rate of an impinging jet in cross-flow configuration on a heated wall-mounted cube. The WALE model was used to model the subgrid-scale tensor. The results from the LES are compared with a Reynolds stress model (RSM) and against earlier measurements with identical set-up. A comparison between the results from the predictions and the measurements shows that in general the LES has better agreement with the measurements compared to the RSM and particularly in the stagnation region of the impinging jet.

On the Use of Embedded Meshes in the LES of External Flows

In the present study, the possibility of performing cheap and accurate LES computations using unstructured grids on complex geometries has been examined. The test case considered is a turbulent flow around a thin controlled diffusion airfoil at low speed, with angle of attack of 8° to the incoming free-stream flow. The flow velocity is set to satisfy the chord Reynolds number of 1.2 × 105. Two subgrid models are tested; the classical Smagorinsky model and the WALE model. The predictions are found to be in good agreement with the experimental data both in terms of flow dynamics and pressure spectra. The results are found to be independent of the LES physical models tested herein, although this conclusion is issued with the caveat that a careful grid generation procedure using (2:3 and 3:4 type) refinements was required to reduce the jump size across the different grid resolutions.

火災現象のラージエディシミュレーションにおけるサブグリッドスケールモデルの比較

This paper evaluates the subgrid scale (SGS) models of Large-Eddy Simulation (LES) in the Fire Dynamics Simulator (FDS), which is the Computational Fluid Dynamics (CFD) code developed at the National Institute of Standards and Technology (KIST) for practical use. LES results of three SGS models (Smagorinsky model, Structure-Function model and WALE model) are compared to fire experimental data of fully developed flow fields in a compartment with an opening. On the other hand, the influence of the three SGS models on transient flow fields at an initial stage of compartment fire phenomena was investigated in terms of time evolution of the temperature by a heat detector model. Further, it is employed to study the effect of the SGS models on unsteady flow fields with simple harmonic oscillation, which is used as a very simplified model of ship rolling motion. From the numerical simulations, it is found that there is no critical difference between the results by the above SGS models. This leads to the conclusion that the Smagorinsky model, which is adopted in FDS by default, works well in practical fire dynamics simulations though it is a primitive SGS model in comparison with the other two improved models.

Validation of the LES approach in Kiva‐3V on a square duct geometry

AbstractThe LES approach implemented in the Kiva‐3V code is evaluated on the fully developed flow through a rectangular duct of square cross section. The Reynolds number based on the bulk velocity and duct width is 8000. The number of grid nodes is 96000. Three subgrid‐scale models are compared: the Smagorinsky, the WALE and the Vreman model. The results differ mainly in the predicted shear stress levels. The Smagorinsky model shows a large overprediction of the shear at the walls, whereas both the WALE and Vreman models perform better due to a reduced contribution of the subgrid dissipation. In this study the WALE model gives the best results on simulating the secondary flows and turbulence statistics. Copyright © 2005 John Wiley & Sons, Ltd.

Hurricane Model Experiments with a New Cumulus Parameterization Scheme

A cumulus parameterization scheme that utilizes a one-dimensional cloud model is tested in a revised, axisymmetric hurricane model. The details of how the parameterization scheme may he incorporated into a larger wale model are presented. With a mean tropical sounding, the cumulus parameterization scheme yields a vertical distribution of heating that is appropriate for tropical cyclone development. The structure of the model hurricane and the properties of the convective clouds at various stages of the model storm development are described. The vertical distribution of the cloud-scale heating and the vertical eddy fluxes of heat, moisture and momentum are given as a function of radius from the storm center during the mature stage. The vertical fluxes of heat and moisture cool and dry the lower troposphere while they warm and moisten the upper troposphere. The vertical transport of radial momentum by the cumulus convection is relatively unimportant, however, the transport of tangential momentum is significant in reducing the vertical shear of the tangential wind.