The time sequence signals of instantaneous longitudinal and normal velocity components at different vertical locations in the turbulent boundary layer over a smooth flat plate have been finely measured by constant tem...The time sequence signals of instantaneous longitudinal and normal velocity components at different vertical locations in the turbulent boundary layer over a smooth flat plate have been finely measured by constant temperature anemometry of model IFA-300 and X-shaped hot-wire sensor probe in a wind tunnel. The longitudinal and normal velocity components have been decomposed into multi-scales by wavelet transform. The upward eject and downward sweep motions in a burst process of coherent structure have been detected by the maximum energy criterion of identifying burst event in wall turbulence through wavelet analysis. The relationships of phase-averaged waveforms among longitudinal velocity component, normal velocity component and Reynolds stress component have been studied through a correlation function method. The dynamics course of coherent structures and their effects on statistical characteristics of turbulent flows are analyzed.展开更多
Reliable turbulent channel flow databases at several Reynolds numbers have been established by large eddy simulation (LES), with two of them validated by comparing with typical direct numerical simulation (DNS) result...Reliable turbulent channel flow databases at several Reynolds numbers have been established by large eddy simulation (LES), with two of them validated by comparing with typical direct numerical simulation (DNS) results. Furthermore, the statistics, such as velocity profile, turbulent intensities and shear stress, were obtained as well as the temporal and spatial structure of turbulent bursts. Based on the LES databases available, the conditional sampling methods are used to detect the structures of burst events. A method to deterimine the grouping parameter from the probability distribution function (pdf) curve of the time separation between ejection events is proposed to avoid the errors in detected results. And thus, the dependence of average burst period on thresholds is considerably weakened. Meanwhile, the average burst-to- bed area ratios are detected. It is found that the Reynolds number exhibits little effect on the burst period and burst-to-bed area ratio.展开更多
In this paper the concentration profile in bed load layer is derived based onkinetic theory. According to observations, particles moving in near wall region behave differentlyduring ejection and sweeping of turbulence...In this paper the concentration profile in bed load layer is derived based onkinetic theory. According to observations, particles moving in near wall region behave differentlyduring ejection and sweeping of turbulence burst, as indicates that they are subject to differentinfluences from turbulence, and therefore, the forces acting on particles are not the same.Consequently, particles moving in bed load layer are classified into two groups, one lifted upwardby ejections, the other carried back to bed by sweepings, and the forces corresponding to upward anddownward motions are proposed. By solving the basic transport equation of kinetic theory, thevelocity distribution functions, upward and downward fluxes of particles in bed load layer arederived. Upon assumption of e-quilibrium sediment transport, concentration profile in bed load layeris obtained. Verification is also presented in this paper, which shows that the concentrationprofile produced by the relation proposed in this paper agrees with observations well.展开更多
The streamwise velocity components at different vertical heights in wall turbulence were measured. Wavelet transform was used to study the turbulent energy spectra, indicating that the global spectrum results from the...The streamwise velocity components at different vertical heights in wall turbulence were measured. Wavelet transform was used to study the turbulent energy spectra, indicating that the global spectrum results from the weighted average of Fourier spectrum based on wavelet scales. W＇avelet transform with more vanishing moments can express the declining of turbulent spectrum. The local wavelet spectrum shows that the physical phenomena such as deformation position in the boundary layer, and the or breakup of eddies are related to the vertical energy-containing eddies exist in a multi-scale form. Moreover, the size of these eddies increases with the measured points moving out of the wall. In the buffer region, the small scale energy-containing eddies with higher frequency are excited. In the outer region, the maximal energy is concentrated in the low-frequency large-scale eddies, and the frequency domain of energy-containing eddies becomes narrower.展开更多
Wavelet Variable Interval Time Average (WVITA) is introduced as a method incorporating burst event detection in wall turbulence. Wavelet transform is performed to unfold the longitudinal fluctuating velocity time seri...Wavelet Variable Interval Time Average (WVITA) is introduced as a method incorporating burst event detection in wall turbulence. Wavelet transform is performed to unfold the longitudinal fluctuating velocity time series measured in the near wall region of a turbulent boundary layer using hot-film anemometer. This unfolding is both in time and in space simultaneously. The splitted kinetic of the longitudinal fluctuating velocity time series among different scales is obtained by integrating the square of wavelet coefficient modulus over temporal space. The time scale that related to burst events in wall turbulence passing through the fixed probe is ascertained by maximum criterion of the kinetic energy evolution across scales. Wavelet transformed localized variance of the fluctuating velocity time series at the maximum kinetic scale is put forward instead of localized short time average variance in Variable Interval Time Average (VITA) scheme. The burst event detection result shows that WVITA scheme can avoid erroneous judgement and solve the grouping problem more effectively which is caused by VITA scheme itself and can not be avoided by adjusting the threshold level or changing the short time average interval.展开更多
The grand unified theory (GUT) originated in mathematics with this question: why are there long standing unsolved problems in mathematics, e.g., Fermat’s conjecture (also known as Fermat’s last theorem (FLT))? The a...The grand unified theory (GUT) originated in mathematics with this question: why are there long standing unsolved problems in mathematics, e.g., Fermat’s conjecture (also known as Fermat’s last theorem (FLT))? The answer came quickly: its underlying fields—foundations and the real number system—are defective. In particular, formal logic is inapplicable to mathematics (language of science) and the real number system is inconsistent. Critique-rectification of these fields was undertaken leading to a new mathematical methodology and the consistent new real number system that provides the main mathematics of GUT. Similar question was posed in physics: why are there long standing problems, e.g., the gravitational n-body and turbulence problems? The answer: the present methodology, quantitative modeling is inadequate and the remedy is a new methodology—qualitative mathematics and modeling that solved these problems and provided the initial formulation of GUT. This paper presents the basic logic of GUT and its fundamental concepts, particularly, the superstring or fundamental building block of matter.展开更多
By use of the LDV, experimental investigation was carried out for a turbulent boundary layer which was disturbed with an electric-magnetic vibrating ribbon. It is found that, in the how, the response of the disturbanc...By use of the LDV, experimental investigation was carried out for a turbulent boundary layer which was disturbed with an electric-magnetic vibrating ribbon. It is found that, in the how, the response of the disturbance contains harmonic components besides the fundamental frequency of the ribbon vibration. The fundamental and harmonic disturbances can also enhance the energy of of the frequency components around them. In the experiments, the regular disturbance was introduced in the outer region of the boundary layer. Under the given flow conditions, they can significantly influence the downstream coherent structures in the wall region by suppressing the bursts and increasing their period. The effect on the burst period depends on the disturbing frequency.展开更多
Based on the analysis of the known quantitative observations and qualitative measurements in the near wall region of the flow over a smooth wall, the distribution of the skewness factor in the vertical direction has b...Based on the analysis of the known quantitative observations and qualitative measurements in the near wall region of the flow over a smooth wall, the distribution of the skewness factor in the vertical direction has been discussed for the openchannel flow over a fully roughened wall. It is found that when H/ks > 1. 0,S >0 is obtained in the range of y/H <0. 2, which means that there exist the low speed streaks, i. e. the turbulence of the now is produced by the phenomenon called 'burst'. For H/ks <1. 0, which belongs to the large-scale roughness case, the turbulence will be produced in another way. Moreover, the burst period is also discussed in this paper.展开更多
基金the National Natural Science Foundation of China (Grant No. 10472081)the Program for New Century Excellent Talents in Universities of Ministry of Education of China, Tianjin Science and Technology Development Plan (Grant No. 06TXTJJC13800)
文摘The time sequence signals of instantaneous longitudinal and normal velocity components at different vertical locations in the turbulent boundary layer over a smooth flat plate have been finely measured by constant temperature anemometry of model IFA-300 and X-shaped hot-wire sensor probe in a wind tunnel. The longitudinal and normal velocity components have been decomposed into multi-scales by wavelet transform. The upward eject and downward sweep motions in a burst process of coherent structure have been detected by the maximum energy criterion of identifying burst event in wall turbulence through wavelet analysis. The relationships of phase-averaged waveforms among longitudinal velocity component, normal velocity component and Reynolds stress component have been studied through a correlation function method. The dynamics course of coherent structures and their effects on statistical characteristics of turbulent flows are analyzed.
基金supported by the National Natural Science Foundation of China(Grant Nos.10332050 and 10002023)Innovation Project,CAS.The authors gratefully acknowledge the support of the Opening Research Foundation of the State Key Laboratory of Water Resources and Hydropower Engineering Science(Grant No.2003B003).
文摘Reliable turbulent channel flow databases at several Reynolds numbers have been established by large eddy simulation (LES), with two of them validated by comparing with typical direct numerical simulation (DNS) results. Furthermore, the statistics, such as velocity profile, turbulent intensities and shear stress, were obtained as well as the temporal and spatial structure of turbulent bursts. Based on the LES databases available, the conditional sampling methods are used to detect the structures of burst events. A method to deterimine the grouping parameter from the probability distribution function (pdf) curve of the time separation between ejection events is proposed to avoid the errors in detected results. And thus, the dependence of average burst period on thresholds is considerably weakened. Meanwhile, the average burst-to- bed area ratios are detected. It is found that the Reynolds number exhibits little effect on the burst period and burst-to-bed area ratio.
文摘In this paper the concentration profile in bed load layer is derived based onkinetic theory. According to observations, particles moving in near wall region behave differentlyduring ejection and sweeping of turbulence burst, as indicates that they are subject to differentinfluences from turbulence, and therefore, the forces acting on particles are not the same.Consequently, particles moving in bed load layer are classified into two groups, one lifted upwardby ejections, the other carried back to bed by sweepings, and the forces corresponding to upward anddownward motions are proposed. By solving the basic transport equation of kinetic theory, thevelocity distribution functions, upward and downward fluxes of particles in bed load layer arederived. Upon assumption of e-quilibrium sediment transport, concentration profile in bed load layeris obtained. Verification is also presented in this paper, which shows that the concentrationprofile produced by the relation proposed in this paper agrees with observations well.
基金supported by the National Natural Science Foundation of China (Nos. 10832001 and10872145)the Program for New Century Excellent Talents in Universities of Education Min-istry of China
文摘The streamwise velocity components at different vertical heights in wall turbulence were measured. Wavelet transform was used to study the turbulent energy spectra, indicating that the global spectrum results from the weighted average of Fourier spectrum based on wavelet scales. W＇avelet transform with more vanishing moments can express the declining of turbulent spectrum. The local wavelet spectrum shows that the physical phenomena such as deformation position in the boundary layer, and the or breakup of eddies are related to the vertical energy-containing eddies exist in a multi-scale form. Moreover, the size of these eddies increases with the measured points moving out of the wall. In the buffer region, the small scale energy-containing eddies with higher frequency are excited. In the outer region, the maximal energy is concentrated in the low-frequency large-scale eddies, and the frequency domain of energy-containing eddies becomes narrower.
基金The project supported by the National Natural Science Foundation of China(19732005)the National Climbing Project of China
文摘Wavelet Variable Interval Time Average (WVITA) is introduced as a method incorporating burst event detection in wall turbulence. Wavelet transform is performed to unfold the longitudinal fluctuating velocity time series measured in the near wall region of a turbulent boundary layer using hot-film anemometer. This unfolding is both in time and in space simultaneously. The splitted kinetic of the longitudinal fluctuating velocity time series among different scales is obtained by integrating the square of wavelet coefficient modulus over temporal space. The time scale that related to burst events in wall turbulence passing through the fixed probe is ascertained by maximum criterion of the kinetic energy evolution across scales. Wavelet transformed localized variance of the fluctuating velocity time series at the maximum kinetic scale is put forward instead of localized short time average variance in Variable Interval Time Average (VITA) scheme. The burst event detection result shows that WVITA scheme can avoid erroneous judgement and solve the grouping problem more effectively which is caused by VITA scheme itself and can not be avoided by adjusting the threshold level or changing the short time average interval.
文摘The grand unified theory (GUT) originated in mathematics with this question: why are there long standing unsolved problems in mathematics, e.g., Fermat’s conjecture (also known as Fermat’s last theorem (FLT))? The answer came quickly: its underlying fields—foundations and the real number system—are defective. In particular, formal logic is inapplicable to mathematics (language of science) and the real number system is inconsistent. Critique-rectification of these fields was undertaken leading to a new mathematical methodology and the consistent new real number system that provides the main mathematics of GUT. Similar question was posed in physics: why are there long standing problems, e.g., the gravitational n-body and turbulence problems? The answer: the present methodology, quantitative modeling is inadequate and the remedy is a new methodology—qualitative mathematics and modeling that solved these problems and provided the initial formulation of GUT. This paper presents the basic logic of GUT and its fundamental concepts, particularly, the superstring or fundamental building block of matter.
基金The National Natural Science Foundation of China
文摘By use of the LDV, experimental investigation was carried out for a turbulent boundary layer which was disturbed with an electric-magnetic vibrating ribbon. It is found that, in the how, the response of the disturbance contains harmonic components besides the fundamental frequency of the ribbon vibration. The fundamental and harmonic disturbances can also enhance the energy of of the frequency components around them. In the experiments, the regular disturbance was introduced in the outer region of the boundary layer. Under the given flow conditions, they can significantly influence the downstream coherent structures in the wall region by suppressing the bursts and increasing their period. The effect on the burst period depends on the disturbing frequency.
文摘Based on the analysis of the known quantitative observations and qualitative measurements in the near wall region of the flow over a smooth wall, the distribution of the skewness factor in the vertical direction has been discussed for the openchannel flow over a fully roughened wall. It is found that when H/ks > 1. 0,S >0 is obtained in the range of y/H <0. 2, which means that there exist the low speed streaks, i. e. the turbulence of the now is produced by the phenomenon called 'burst'. For H/ks <1. 0, which belongs to the large-scale roughness case, the turbulence will be produced in another way. Moreover, the burst period is also discussed in this paper.
