LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER

1. INTRODUCTIONFreesurface turbulent flow exists widely in engineering. Due to difficulties in measurement and simulation, very little has been understood about the structures and transport mechanism of turbulence near the freesurface. Komori and Ueda…     

LARGE EDDY SIMULATION OF PULSATING TURBULENT OPEN CHANNEL FLOW

Pulsating turbulent open channel flow has been investigated by the u.se of I.arge Eddy Simulation (I.ES) technique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulent SGS stress to closure the governing equations.Three-dimensional filtered Navier-Stokes equations are numerically solved by a fractional-- step method. The objective of this study is to deal with the behavior of the pulsating turbulent open channel flow and to examine the reliability of the I.ES approach for predicting the pulsating turbulent flow. In this study, the Reynolds number (Re,) is chosen as 180 based on the friction velocity and the channel depth, The frequency of the driving pressure gradient for the pulsating turbulent flow ranges low, medium and high value, Statistical turbulence quantities as well as the flow structures are analyzed.     

LARGE EDDY SIMULATION OF PARTICLE TRANSPORT IN FULLY DEVELOPED VERTICAL TURBULENT CHANNEL FLOW

Fully developed vertical turbulent channel flow with particle transport was investigated by use of Large Eddy Simulation (LES) approach coupled with dynamic the SubGrid Scale (SGS) model. It was assumed that the motion of each particle is followed in a Lagrangian frame of reference driven by the forces exerted by fluid motion and gravity under the condition of one-way coupling. The goal of this study is to investigate the effectiveness of the I.ES technique for predicting particle transport in turbulent flow and the behavior of particle-laden turbulent channel flow for three kinds of particles at different Stokes numbers. To depict the behavior of particle-laden turbulent channel flow, statistical quantities including particle fluctuation and fluid-particle velocity correlation, and visualization of the particle number density field were analyzed.     

LARGE EDDY SIMULATION OF THERMALLY-STRATIFIED TURBULENT CHANNEL FLOW WITH TEMPERATURE OSCILLATION ON THE BOTTOM WALL

Thermally-stratified shear turbulent channel flow with temperature oscillation on the bottom wall of the channel was investigated with the Large Eddy Simulation (LES) approach coupled with dynamic Sub-Grid-Scale (SGS) models. The effect of temperature oscillation on the turbulent channel flow behavior was examined. The phase-averaged velocities and temperature, and flow structures at different Richardson numbers and periods of the oscillation was analyzed.     

LARGE EDDY SIMULATION （LES） OF TURBULENT FLOW BY FINITE DIFFERENCE METHOD

A Large Eddy Simulation (LES) technique was applied to solve the turbulent channel flow for Rer = 150.Three types of turbulence models are employed, such as the Smagorinsky model, the Dynamic Sub-Grid Scale(SGS) model and the Generalized Normal Stress (GNS) model. The simulated data in time series for the LES were averaged in both time and space to carry out the statistical analysis. Results of LES were compared with that of a DNS. As an application, a LES technique was used for 2D body in order to check the validation by investigating the turbulent vortical motion around the afterbody with a slant angle.     

DIRECT NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN A WALL-NORMAL ROTATING CHANNEL FLOW

1. INTRODUCTIONTurbulent flows with heat transfer in rotatingframe exist in a variety of industrial , geophysicaland astrophysical applications . The rotation in-duces additional body forces ,i .e .,centrifugal andCoriolis forces , acting on the turbulent…     

LARGE EDDY SIMULATION OF OPEN CHANNEL FLOWS WITH NONSUBMERGED VEGETATION

Results of several Large Eddy Simulations (LES) of open channel flows with non-submerged vegetation are presented in this article. It is shown that the vegetation can make the flow structure in the mainstream direction uniform for both supercritical and subcritical flows. For subcritical flows, the LES results of the ensemble-average of time-averaged velocity distributions at four vertical sections around a single plant are in good agreement with measurements. The velocity sees double peaks at the upper and lower positions of flows. For supercritical flows, the ensemble-average velocities see some discrepancy between LES and measurement results. Some secondary flow eddies appear near the single plant, and they just locate in the positions of the double peaks in stream-wise velocity profiles. It is also found that the vegetation drag coefficient deceases as the Froude number increases.     

THREE-DIMENSIONAL LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT FLOW IN OPEN CHANNEL WITHIN SUBMERGED VEGETATION DOMAIN

1 .　INTRODUCTIONInactualrivers ,theriverbediscommonlycoveredbyvegetation .Thevegetationinriversplaysanimportantroleontheenvironmentalfunc tionoftherivers,thatis,theamenitytohumanlife ,livingspaceformanylives ,purificationofwaterqualityandsoon .However ,thevegetationinriversalsoplaysakeyroleonthecarryingca pacityofachannelwithfloodplains .Therefore ,thehydraulicsoftheflowwithvegetationshouldbemoreimprovedorrefined .Logicalexplanationandaccurateevaluationaboutturbulentflowinopenchannelwith…     

AN ADAPTIVE CONTROL STRATEGY FOR PROPER MESH DISTRIBUTION IN LARGE EDDY SIMULATION

The Filtering Grid Scale (FGS) of sub-grid scale models does not match with the theoretical Proper FGS (PFGS) because of the improper mesh. Therefore, proper Large Eddy Simulation (LES) Mesh is very decisive for better results and more economical cost. In this work, the purpose is to provide an adaptive control strategy for proper LES mesh with turbulence theory and CFD methods. A new expression of PFGS is proposed on the basis of ?5/3 law of inertial sub-range and the proper mesh of LES can be built directly from the adjustment of RANS mesh. A benchmark of the backward facing step flow at Re = 5147 is provided for application and verification. There are three kinds of mesh sizes, including the RANS mesh, LAM (LES of adaptive-control mesh), LFM (LES of fine mesh), employed here. The grid number of LAM is smaller than those of LFM evidently, and the results of LAM are in a good agreement with those of DNS and experiments. It is revealed that the results of LAM are very close to those of LFM. The conclusions provide positive evidences for the novel strategy.     

INTRINSIC FEATURES OF TURBULENT FLOW IN STRONGLY 3-D SKEW BLADE PASSAGE OF A FRANCIS TURBINE

The turbulent flow, with the Reynolds number of 5.9× 105, in the strongly 3-D skew blade passage of a true Francis hydro turbine was simulated by the Large Eddy Simulation (LES) approach to investigate the spatial and temporal distributions of the fully developed turbulence in the passage with strongly 3-D complex geometry. The simulations show that the strong three-dimensionality of the passage has a great amplification effect on the turbulence in the passage, and the distributions of the turbulence are diversely nonuniform, for instance, the rise of turbulent kinetic energy in the lower 1/3 region of the passage is more than 45%, whereas its rise in the upper 1/3 region is less than 1%. With the LES approach, the details of the flow structures at the near-wall surfaces of the blades could be obtained. Several turbulent spots were captured.     

LARGE EDDY SIMULATION FOR PLUNGING BREAKER WAVE

1 .　INTRODUCTIONInthenear shoreregion ,aswavespropagateintoshallowwater ,theprocessofshoalingleadstotheincreaseofwaveheight ,however ,thisprocesscannotcontinue ,andatacertain positionthewavebreaks .Inpractice ,breakingwavesarepow erfulagentsforgeneratingturbulence ,whichplaysanimportantroleinmostofthefluiddynamicalprocessesthroughoutthesurfzone ,suchaswavetransformation ,generationofnear shorecurrent ,diffusionofmaterials ,andsedimenttransporta tion .Manynumericalstudieshavebeenconductedt…     

NUMERICAL STUDY ON AIR FLOW AROUND AN OPENING WITH LARGE EDDY SIMULATION

Jet characteristics of air supply opening in a ventilating or an air-conditioning system is primarily decided by the folw state in the duct connected to the opening. It is valuable to study the opening jet characteristics and the flow state in a duct. In this study, the Large Eddy Simulation (LES) technique combined with the Tarlor-Galerkin Finite Element Method ( FEM) in Computational Fluid Dynamics (CFD) was applied to the problem. The 3-D flow fields in ducts around air supply opening under typical conditions were investigated by numerical simulation as well as experimental measurements. Numerical results agree well with the available experimental data. It indicates that the LES method is available under the conditions with complicated boundaries and inner accompanied by anisotropic large-scale eddies, and it is credible to predict the jet deflection characteristics around an opening.     

LARGE-EDDY SIMULATION OF TURBULENT FLOW CONSIDERING INFLOW WAKES IN A FRANCIS TURBINE BLADE PASSAGE

Turbulent flow in a 3-D blade passage of a Francis hydro turbine was simulated with the Large Eddy Simulation (LES) to investigate the spatial and temporal distributions of the turbulence when strongly distorted wakes in the inflow sweep over the passage. In a suitable consideration of the energy exchanging mechanism between the large and small scales in the complicated passage with a strong 3-D curvature,one-coefficient dynamic Sub-Grid-Scale (SGS) stress model was used in this article. The simulations show that the strong wakes in the inflow lead to a flow separation at the leading zone of the passage,and to form a primary vortex in the span-wise direction. The primary span-wise vortex evolves and splits into smaller vortex pairs due to the constraint of no-slip wall condition,which triggers losing stability of the flow in the passage. The computed pressures on the pressure and suction sides agree with the measured data for a working test turbine model.     

LARGE EDDY SIMULATION OF VERTICAL JET IMPINGEMENT WITH A FREE SURFACE

1. INTRODUCTION When wastewater is discharged into rivers, lakes or oceans, it usually leads to the formulation of turbulent jet with a free surface. If the ambient water depth is shallow, the jet will impinge on the water surface and the confinement of f…     

AN IMPROVED DYNAMIC SUBGRID-SCALE STRESS MODEL

1 .　INTRODUCTIONFlowsincurvedductsoccurindiverseapplicationssuchascentrifugalpumps,turbines ,aircraftintakes,riverbends ,andsoon .Acharacteristic ,whichdistin guishessuchflowsfromthoseinstraightducts ,isthegenerationofstreamwisevorticity ,orsecondarymo tion ,resultinginapressurelossandthespatialredis tributionofstreamwisevelocitywithintheduct .Sore searchesonflowsthroughbendsaremoremeaningfulforengineeringapplications .AsaresultoftherapidadvancementofcomputercapabilityandComputationalFl…     

THE LARGE EDDY SIMULATION OF STRONGLY CURVED OPEN CHANNEL FLOW

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TURBULENT MIXING AND EVOLUTION IN A STABLY STRATIFIED FLOW WITH A TEMPERATURE STEP

Large-Eddy Simulation(LES)is applied to examine the turbulent mixing and evolution in a stably stratified flow with a thermally sharp interface.Turbulent velocity intensities and turbulent kinetic energy are analyzed by considering the mean shear and stratification effects.The evolution of turbulent mixing layer and turbulent structures are mainly investigated.The results show that the streamwise intensities are much larger than the vertical intensities,and vertical fluctuations decay more rapidly at the presence of stratification.The qualitatively computational results suggest that the mixing layer,defined by the mean temperature,inclines to the side with small inlet velocity.The evolution of the half-width of the mixing layer shows two different slopes.The turbulent structure with high vorticity is restricted in the mixing layer especially in strong stratified cases.     

A LARGE EDDY SIMULATION TURBULENCE MODEL FOR COASTAL SEAS AND SHALLOW WATER PROBLEMS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＬＥＳａｐｐｒｏａｃｈｏｒｉｇｉｎａｔｅｄｆｒｏｍｔｈｅｎｅｅｄｓｏｆｍｅｔｅｏｒｏｌｏｇｉｓｔｓｔｏｐｒｅｄｉｃｔｏｒｓｉｍｕｌａｔｅｔｈｅｇｌｏｂａｌｗｅａｔｈ ｅｒ .ＧｅｎｅｒａｌｌｙＳｍａｇｏｒｉｎｓｋｙ (196 3)ｗａｓｃｒｅｄｉｔｅｄｗｉｔｈｔｈｅｉｎｉｔｉａｌｄｅｖｅｌｏｐｍｅｎｔｏｆＬＥＳ .ＴｈｅｆｉｒｓｔａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅＬＥＳａｐｐｒｏａｃｈｔｏｐｒｏｂｌｅｍｓｏｆｅｎｇｉｎｅｅｒｉｇｉｎｔｅｒｅｓｔｗａｓｍａｄｅｂｙＤｅａｒｄｏｒ…     

EXPERIMENTAL STUDY OF 3-D TURBULENT BEND FLOWS IN OPEN CHANNEL

1.INTRODUCTION Mostnaturalflowsareturbulent,andthenat uralriversareprevalentlymeandering.Mostofthe riverbendsarethosewithnot fully developedcir culationcurrentsonly,inwhichcentralanglesfor thebendsaresmallerthan180°,even90°.These bendflowsarecharacterizedbythedevelopmentoflateralcirculationcurrentsandbythenot fully offsetsofmainflow,withobvious3Dfeatures.Soinhydraulicengineeringandnavigationengi neering,itisimportantandnecessarytoinvesti gatethe3Dturbulentcharactersofbendflow.Be causet…     

LARGE-EDDY AND DETACHED-EDDY SIMULATIONS OF THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER

The separated turbulent flow around a circular cylinder is investigated using Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES, or hybrid RANS/LES methods), and Unsteady Reynolds-Averaged Navier-Stokes (URANS). The purpose of this study is to examine some typical simulation approaches for the prediction of complex separated turbulent flow and to clarify the capability of applying these approaches to a typical case of the separated turbulent flow around a circular cylinder. Several turbulence models, i.e. dynamic Sub-grid Scale (SGS) model in LES, the DES-based Spalart-Allmaras (S-A) and k ? ω Shear-Stress-Transport (SST) models in DES, and the S-A and SST models in URANS, are used in the calculations. Some typical results, e.g., the mean pressure and drag coefficients, velocity profiles, Strouhal number, and Reynolds stresses, are obtained and compared with previous computational and experimental data. Based on our extensive calculations, we assess the capability and performance of these simulation approaches coupled with the relevant turbulence models to predict the separated turbulent flow.