In this paper four families of orthogonal wavelets are applied to analyze the turbulent counter gradient transport phenomena in fully developed asymmetric channel flows. The results show that: (1) In the instance of c...In this paper four families of orthogonal wavelets are applied to analyze the turbulent counter gradient transport phenomena in fully developed asymmetric channel flows. The results show that: (1) In the instance of counter gradient transport, the principal scale of the coherent structure is responsible for the strong local counter gradient transport; (2) Counter gradient transport phenomena have a strong effect on the intermittency of turbulence; (3) Non-Gaussian part of the principal coherent structure is essential for counter gradient transport phenomena.展开更多
The counter gradient transport phenomena on momentum, energy and passive scalar in turbulent flows were studied by use of the single response friction for TSDIA. As a result, models that can describe qualitatively the...The counter gradient transport phenomena on momentum, energy and passive scalar in turbulent flows were studied by use of the single response friction for TSDIA. As a result, models that can describe qualitatively the phenomena are obtained. Then the results are simplified by use of the internal range theory, and the results for lower degrees agree with results of predecessor. Finally the counter gradient-transport phenomena in channel flow and circular wake flow are analyzed.展开更多
The empirical mode decomposition （EMD） is used to study the scale properties of turbulent transport and coherent structures based on velocity and temperature time series in stably stratified turbulence. The analysis...The empirical mode decomposition （EMD） is used to study the scale properties of turbulent transport and coherent structures based on velocity and temperature time series in stably stratified turbulence. The analysis is focused on the scale properties of intermittency and coherent structures in different modes and the contributions of energy-contained coherent structures to turbulent scalar counter-gradient transport （CGT）. It is inferred that the velocity intermittency is scattered to more modes with the development of the stratified flow, and the intermittency is enhanced by the vertical stratification, especially in small scales. The anisotropy of the field is presented due to different time scales of coherent structures of streamwise and vertical velocities. There is global counter-gradient heat transport close to the turbulence-generated grid, and there is local counter-gradient heat transport at certain modes in different positions. Coherent structures play a principal role in the turbulent vertical transport of temperature.展开更多
In this paper, the turbulence characteristics were numerically investigatedin an asymmetric turbulent channel flow and the computational results were compared with therelevant experimental data. It shows that the resu...In this paper, the turbulence characteristics were numerically investigatedin an asymmetric turbulent channel flow and the computational results were compared with therelevant experimental data. It shows that the results are consistent with the experiments and thereexist Counter-Gradient Momentum Transport (CGMT) phenomena in the central region near the smoothwall, and this region is as large as 6 percent of the channel width. In addition, a region, in whichCounter-Gradient-Transport (CGT) phenomena occur more evidently, is found close to the rough wall.These results can help to gain a deeper insight into the mechanism of CGT phenomena.展开更多
Turbulence structures and turbulent Counter-Gradient Transport（CGT） properties in the stratified flows with a sharp temperature interface are investigated by experimental measurements using LIF and PIV, by LES and b...Turbulence structures and turbulent Counter-Gradient Transport（CGT） properties in the stratified flows with a sharp temperature interface are investigated by experimental measurements using LIF and PIV, by LES and by correlation analysis.展开更多
By using the Reynolds Stress Closure Model (RSM), turbulentCounter-Gradient-Transport (CGT) phenomenon was numerically investigated in asymmetric flow with ajet, and the computational results were compared with experi...By using the Reynolds Stress Closure Model (RSM), turbulentCounter-Gradient-Transport (CGT) phenomenon was numerically investigated in asymmetric flow with ajet, and the computational results were compared with experimental data. The computational resultsshow that the negative turbulent energy production only appears at some certain stations in CGTregion, this fact indicates that the CGT phenomenon exists more widely than the negative turbulentenergy production; while the CGT region exists all along, it gradually shrinks in the favorablepressure 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 whereuv = 0 switched sides, relative to where partial deriv U/partial deriv y = 0, from favorablepressure gradient to adverse pressure gradient. The pressure gradient takes an important effect onthe region of negative turbulent energy production and CGT.展开更多
Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivit...Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.展开更多
Wavelet analysis is applied to study the global and local scaling exponents in fully developed asymmetric channel flow. Global exponents are calculated by orthogonal wavelets and Extended Scaling Similarity(ESS). The ...Wavelet analysis is applied to study the global and local scaling exponents in fully developed asymmetric channel flow. Global exponents are calculated by orthogonal wavelets and Extended Scaling Similarity(ESS). The results show that the flow in an asymmetric channel flow exhibits different characteristics of intermittency from that in a symmetric flow. It is also shown that the intermittency property of the streamwise fluctuations is different from that of vertical fluctuations, and the intermittency does not decay with the increase of the distance from the wall. In addition, the Continuous Wavelet Transform(CWT) method is found to be unreliable to calculate the local scaling components. Finally, it is pointed out that the existence and the significance of negative local scaling components need further study.展开更多
基金The project supported by the National Natural Science Foundation of China(10272071.10472063)
文摘In this paper four families of orthogonal wavelets are applied to analyze the turbulent counter gradient transport phenomena in fully developed asymmetric channel flows. The results show that: (1) In the instance of counter gradient transport, the principal scale of the coherent structure is responsible for the strong local counter gradient transport; (2) Counter gradient transport phenomena have a strong effect on the intermittency of turbulence; (3) Non-Gaussian part of the principal coherent structure is essential for counter gradient transport phenomena.
文摘The counter gradient transport phenomena on momentum, energy and passive scalar in turbulent flows were studied by use of the single response friction for TSDIA. As a result, models that can describe qualitatively the phenomena are obtained. Then the results are simplified by use of the internal range theory, and the results for lower degrees agree with results of predecessor. Finally the counter gradient-transport phenomena in channel flow and circular wake flow are analyzed.
基金supported by the National Natural Science Foundation of China(Nos.1110211411172179+2 种基金11332006and 11572203)the Innovation Program of Shanghai Municipal Education Commission(No.13YZ124)
文摘The empirical mode decomposition （EMD） is used to study the scale properties of turbulent transport and coherent structures based on velocity and temperature time series in stably stratified turbulence. The analysis is focused on the scale properties of intermittency and coherent structures in different modes and the contributions of energy-contained coherent structures to turbulent scalar counter-gradient transport （CGT）. It is inferred that the velocity intermittency is scattered to more modes with the development of the stratified flow, and the intermittency is enhanced by the vertical stratification, especially in small scales. The anisotropy of the field is presented due to different time scales of coherent structures of streamwise and vertical velocities. There is global counter-gradient heat transport close to the turbulence-generated grid, and there is local counter-gradient heat transport at certain modes in different positions. Coherent structures play a principal role in the turbulent vertical transport of temperature.
文摘In this paper, the turbulence characteristics were numerically investigatedin an asymmetric turbulent channel flow and the computational results were compared with therelevant experimental data. It shows that the results are consistent with the experiments and thereexist Counter-Gradient Momentum Transport (CGMT) phenomena in the central region near the smoothwall, and this region is as large as 6 percent of the channel width. In addition, a region, in whichCounter-Gradient-Transport (CGT) phenomena occur more evidently, is found close to the rough wall.These results can help to gain a deeper insight into the mechanism of CGT phenomena.
文摘Turbulence structures and turbulent Counter-Gradient Transport（CGT） properties in the stratified flows with a sharp temperature interface are investigated by experimental measurements using LIF and PIV, by LES and by correlation analysis.
文摘By using the Reynolds Stress Closure Model (RSM), turbulentCounter-Gradient-Transport (CGT) phenomenon was numerically investigated in asymmetric flow with ajet, and the computational results were compared with experimental data. The computational resultsshow that the negative turbulent energy production only appears at some certain stations in CGTregion, this fact indicates that the CGT phenomenon exists more widely than the negative turbulentenergy production; while the CGT region exists all along, it gradually shrinks in the favorablepressure 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 whereuv = 0 switched sides, relative to where partial deriv U/partial deriv y = 0, from favorablepressure gradient to adverse pressure gradient. The pressure gradient takes an important effect onthe region of negative turbulent energy production and CGT.
基金jointly supported by the National Natural Science Foundation of China[grant numbers 41975018 and 41675012]the National Key Research and Development Program of China[grant number 2017YFC0209605]。
文摘Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.
文摘Wavelet analysis is applied to study the global and local scaling exponents in fully developed asymmetric channel flow. Global exponents are calculated by orthogonal wavelets and Extended Scaling Similarity(ESS). The results show that the flow in an asymmetric channel flow exhibits different characteristics of intermittency from that in a symmetric flow. It is also shown that the intermittency property of the streamwise fluctuations is different from that of vertical fluctuations, and the intermittency does not decay with the increase of the distance from the wall. In addition, the Continuous Wavelet Transform(CWT) method is found to be unreliable to calculate the local scaling components. Finally, it is pointed out that the existence and the significance of negative local scaling components need further study.
