NUMERICAL INVESTIGATION OF TURBULENT COUNTER-GRADIENT-TRANSPORT IN ASYMMETRIC FLOW WITH A JET

By using the Reynolds Stress Closure Model (RSM), turbulent Counter-Gradient-Transport (CGT) phenomenon was numerically investigated in asymmetric flow with a jet, and the computational results were compared with experimental data. The computational results show that the negative turbulent energy production only appears at some certain stations in CGT region, this fact indicates that the CGT phenomenon exists more widely than the negative turbulent energy production; while the CGT region exists all along, it gradually shrinks in the favorable pressure gradient zone until the position of the wing central part is reached, where it vanishes, but it appears in the adverse pressure gradient region in addition, the location in the flow where uυ = 0 switched sides, relative to where aU/au = 0, from favorable pressure gradient to adverse pressure gradient. The pressure gradient takes an important effect on the region of negative turbulent energy production and CGT.     

AN INVESTIGATION OF TURBULENT HEAT TRANSFER IN CHANNEL FLOWS BY LARGE EDDY SIMULATION

Large Eddy Simulation (LES) of fully developed turbulent channel flow with heat transfer was performed to investigate the effects of the Reynolds number on the turbulence behavior. In the present study, the bottom wall of the channel was cooled and the top wall was heated. The Reynolds numbers, based on the central mean-velocity and the half-width of the channel, were chosen as 4000, 6000, 104 and 2×104, and the Prandtl number as 1.0. To validate our calculations, the present results were compared with available data obtained by Direct Numerical Simulation (DNS), which proves to be in good agreement with each other. To reveal the effects of the Reynolds number, some typical quantities, including the velocity fluctuations, temperature fluctuation, heat fluxes and turbulent Prandtl number, were studied.     

INVESTIGATION OF TURBULENCE STRUCTURES AND TURBULENT COUNTER-GRADIENT TRANSPORT PROPERTIES IN STRATIFIED FLOWS

BRIEF INTRODUCTION OF THE PAPER: In this article, the collective effects of mean shear and stratification on turbulence structure and turbulent scalar Counter-Gradient Transport(CGT) features are studied principally. The set of experiments are conducted i…     

DRAG REDUCTION IN A TURBULENT CHANNEL FLOW WITH HYDRO- PHOBIC WALL

This paper investigates a theoretical prediction of friction drag reduction in turbulent channel flow which is achieved by using superhydrophobic surfaces. The effect of the hydrophobic surface is considered to be a slip boundary condition on the wall, and this new boundary condition is added to Large Eddy Simulation (LES) equations. The predicted drag reduction at Reτ=180 is approximately 30%, which concurs with results obtained from Direct Numerical Simulation (DNS). An important implication of the present finding is that the near-wall turbulence structures are modified with streamwise slip velocity. In addition, a noticeable effect on the turbulence structure occurs when the slip length is greater than a certain value.     

THE STRUCTURE AND SCALE EFFECT OF WALL TURBULENT FLOW

In this paper the structure and scale effect of wall turbulence are investigated.Thecharacteristics of the turbulence structure in the wall region is described.The fact that the turbu-lence in whole flow field is controlled mainly by the structure of wall turbulence is demonstrat-ed.Discussion is concentrated on the scale effects of the streak structure,the vortex structureand the bursting frequency.     

Scale analysis of turbulent channel flow with varying pressure gradient简

In this paper orthogonal wavelet transformations are applied to decompose experimental velocity signals in fully develo-ped channel flows with varying pressure gradient into scales. We analyze the time series from turbulent data, to obtain the statistical characteristics, correlations between the adjacent scales and the principal scale of coherent structures in different scales by wavelet transformations. The results show that, in the counter gradient transport （CGT） region, skewness factors and flatness factors deviate strongly from the corresponding values of Gaussian distribution on certain scales. PDFs on each scale confirm this observation. Scale-scale correlations show further that the fluctuations on some certain special scales are more intermittent than nearby. Principal scale of coherent structure is coincident with the scales on which the statistical properties depart from Gaussian distribution. These features are the same for different families of wavelets, and it also shows some different features in the region between favorable pressure gradient and adverse pressure gradient.     

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 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.     

NUMERICAL STUDY OF TURBULENT IMPINGING JET WITH A REFINED k-ε MODEL

1.　INTRODUCTIONJet impingement flows are frequently used in industrial practice for their high rate ofheat and mass transfer.Their employment is common but also diverse and typical applica-tions includemany heating,cooling and drying processessuch asthe manufacturing of print-ed wiring board,printing processes,production of foodstuffs,de-icing of aircraft wings,cooling of electronic elements and package and cooling of turbine aerofoils.The high heattransfer rate are especially needed to a…     

PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED SPIRAL COIL INSERT

The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Compared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous disturbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the reduction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enhanced in this area.     

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…     

INFLUENCE OF YOUNG'S MODULUS ON DRAG-REDUCTION IN TURBULENT FLOW USING FLEXIBLE TUBES

In order to develop technologies of friction drag reduction with a flexible tube to be used for water transport, experimental studies were carried out on the influence of Young's modulus on the turbulent drag reduction. The friction coefficients of flexible tubes with different Young's modulus were examined by using a sleeve-tube structure. The fluctuating vibration of the outer wall and the fluctuating pressure on the inner wall of the tubes were measured with a laser displacement sensor and a pressure sensor. The results are as follows. The smaller the Young's modulus of a flexible tube and the larger the Reynolds number, the larger the turbulent drag reduction rates become. The transition from laminar flow to turbulent flow can be delayed with an appropriate Young's modulus. Non-dimensional amplitude of fluctuating vibration on the outer wall is smaller than that of a viscous sub-layer thickness, and is positively correlated with the friction drag reduction.     

土石坝渗漏的波速-电阻率联合成像诊断试验研究

本文采用模型试验对三种不同渗漏类型的病险土石坝分别进行波速-电阻率联合成像诊断试验,试验结果表明,采用电阻率成像诊断坝体的渗漏范围具有较高的精度,但在圈定心墙的渗漏通道时,由成像获得的电阻率异常区域较实际渗漏通道大;采用波速成像诊断坝体的渗漏范围时,诊断效果取决于含水量的变化幅度,含水量变化较小的区域,精度较低,但在圈定心墙渗漏通道时,波速成像却具有较高的精度;因此在土石坝渗漏诊断中,采用单一的电阻率成像或波速成像都具有一定局限性,而联合电阻率和波速成像可以有效提高坝体渗漏区域和心墙渗漏通道的诊断精度。     

3-D TURBULENT FLOW SIMULATION FOR THE TAIL WATER CHANNEL

３－ＤＴＵＲＢＵＬＥＮＴＦＬＯＷＳＩＭＵＬＡＴＩＯＮＦＯＲＴＨＥＴＡＩＬＷＡＴＥＲＣＨＡＮＮＥＬＧｕａｎＪｉａｎ－ｙｏｎｇ；ＣｈｅｎＢｉ－ｈｏｎｇ（ＤａｌｉａｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ，Ｄａｌｉａｎ１１６０２３，Ｐ．Ｒ．Ｃｈｉｎａ...     

MODIFIED LOG-WAKE LAWS FOR TURBULENT FLOW OF THE OUTER AND INNER REGIONS IN SMOOTH PIPES

Based on theoretical analysis two modified log-wake laws for turbulent flow in smooth pipes are obtained,one is applicable to the outer region and other one to inner region,the new law for the outer region fits the velocity profile measured in smooth pipes by Zagarola very well and the effect of Reynolds number can be taken into consideration,the velocity profile for inner region satisfies the wall boundary conditions ,equals zero at the pipe wall and smoothly joins up with the velocity profile in outer region,the adopted eddy viscosity model is consistent with Laufer’s,Nunner’s and Reichardt’s experimental data.     

土石坝渗漏的波速-电阻率联合成像诊断试验研究

采用模型试验对3种不同渗漏类型的病险土石坝分别进行了波速-电阻率联合成像诊断试验。试验结果表明,采用电阻率成像诊断坝体的渗漏范围具有较高的精度,但在圈定心墙的渗漏通道时,由成像获得的电阻率异常区域较实际渗漏通道大;采用波速成像诊断坝体的渗漏范围时,诊断效果取决于含水率的变化幅度,含水率变化较小的区域,精度较低,但在圈定心墙渗漏通道时,波速成像却具有较高的精度。因此在土石坝渗漏诊断中,采用单一的电阻率成像或波速成像都具有一定局限性,而联合电阻率和波速成像可以有效提高坝体渗漏区域和心墙渗漏通道的诊断精度。     

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.     

TURBULENT OPEN CHANNEL FLOW SUBJECTED TO THE CONTROL OF A SPANWISE TRAVELING WAVE

Turbulent open channel flows subjected to the control of a spanwise traveling wave have been investigated by means of Direct Numerical Simulation(DNS).The objective of this study is to reveal the response of the near-wall and surface-influenced turbulence to the spanwise traveling wave control.Three typical frequencies of the spanwise traveling wave,i.e.,high-,middle-and low-frequency,corresponding to the exciting periods at 25,50 and 100,are considered to study the turbulence dynamics in the wall and surface regions.To elucidate the behaviors of turbulence statistics,some typical quantities,including the mean velocity,velocity fluctuations and the structures of turbulence fluctuations,are exhibited and analyzed.     

STUDY ON THE MECHANISM OF TURBULENT PRODUCTION AND BURST DETECTION OVER A ROUGH WALL

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