Wavelet spectrum analysis on energy transfer of multi-scale structures in wall turbulence

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.     

用子波分析能量最大准则修正检测壁湍流猝发的mu-level法

将壁湍流脉动速度信号子波分析技术引入壁湍流相干结构猝发检测的研究,基于子波分析能量最大准则确定相干结构猝发的时间尺度,对能量最大时间尺度的子波系数进行子波逆变换,获得能量最大时间尺度的脉动速度信号。根据其自相关函数的波长确定相干结构的平均猝发周期;根据能量最大时间尺度的子波系数的正极大值和负极小值检测壁湍流喷射和扫掠事件,获得壁湍流相干结构喷射和扫掠事件的相位平均波形。该方法可以不需要确定门限值,有效排除了小尺度脉动的干扰。     

子波分析辨识壁湍流猝发事件的能量最大准则

用子波分析的方法，对用热膜测速仪得到的平板湍流边界层中流向脉动速度信号，在时域空间和频域空间同时进行时频双局部化分解．用子波系数研究了壁湍流脉动动能随尺度的分布，提出了确定壁湍流猝发事件时间尺度参数的能量最大准则，用子波逆变换得到了猝发事件对应的速度信号波形     

用VITA法检测壁湍流喷射事件的归组问题

用子波分析和能量最大准则解决了ＶＩＴＡ法检测壁湍流猝发中的喷射事件的归组问题     

用能量最大准则确定VITA法的平均周期

引入了子波变换的方法来确定检测壁湍流猝发事件的VITA法的短时间平均周期T。为了确定VITA法的短时间平均周期T,用子波变换对热膜测速仪测量得到的湍流边界层近壁区域的流向脉动速度的时间序列进行了分解,分解在时域和频域同时进行,根据每一个尺度的子波系数的模的平方在时域的积分得到壁湍流每一个尺度的脉动动能随尺度的分布,用能量最大准则确定与壁湍流猝发事件的时间尺度对应的能量最大的尺度,该尺度也就是VITA法的短时间平均周期T。     

用子波分析修正检测壁湍流猝发的VITA法

应用壁湍流脉动速度信号子波分析的一系列方法对检测壁湍流猝发事件的VITA法进行了修正。其中,用能量最大准则确定VITA法短时间平均周期;以子波变换能量最大尺度脉动速度的短时间平均方差的局部极大值点作为检测函数的中心点,取代了传统VITA法中对短时间周期平均方差选用门限值的方法,避免了VITA法检测结果对门限值的主观经验依赖性,提高了VITA法检测壁湍流猝发事件的客观性和准确性。     

壁湍流相干结构和减阻控制机理

剪切湍流中相干结构的发现是上世纪湍流研究的重大进展之一,这些大尺度的相干运动在湍流的动力学过程中起重要作用,也为湍流的控制指出了新的方向.壁湍流高摩擦阻力的产生与近壁区流动结构密切相关,基于近壁区湍流动力学过程的减阻控制方案可以有效降低湍流的摩擦阻力,但是随着雷诺数的升高, 这些控制方案的有效性逐渐降低.近年来研究发现, 在高雷诺数情况下外区存在大尺度的相干运动,这种大尺度运动对近壁区湍流和壁面摩擦阻力的产生有重要影响,为高雷诺数湍流减阻控制策略的设计提出了新的挑战.该文将对壁湍流相干结构的研究历史加以简单的回顾,重点介绍近壁区相干结构及其控制机理、近年来高雷诺数外区大尺度运动的研究进展,在此基础上提出高雷诺数减阻控制研究的关键科学问题.      

Numerical methods for the solution of the turbulence energy equations in shelf seas

This paper investigates the accuracy of numerical finite difference methods for solving the turbulence kinetic energy equations in thermally stratified shelf seas with wind and tidal mixing. Alternative discretisation methods are presented for both the source terms and the diffusion term in the turbulence kinetic energy equation. It is shown that techniques not widely used in this field maintain greater accuracy at low spatial and temporal resolution than is obtained with commonly used ones, with no added computational cost. Therefore, these techniques are valuable for use in three‐dimensional models. Copyright © 1999 John Wiley & Sons, Ltd.     

用自相关法检测壁湍流的平均猝发周期

本文通过研究湍流脉动速度信号的自相关函数，提出了用自相关函数检测壁湍流平均猝发周期的方法。     

Prediction of turbulence energy dissipation in flexible apron of barrages using numerical method

Barrages form an important component of hydraulic structures constructed to intercept and divert part of the available flow of a river and use it for purposes like irrigation, hydropower and domestic or industrial water supply. A flexible apron is a protection system provided in the barrage to prevent the possibility of the scour hole traveling close to the stilling basin. The turbulence kinetic energy is predicted using a 3D VOF (volume of fluid) realizable k ?? model for both horizontal and depressed flexible aprons placed downstream of the stilling basin of the barrage. The turbulence kinetic energy at the downstream end of the inclined flexible apron is comparably less compared with the horizontal flexible apron for all the cases. Copyright © 2011 John Wiley & Sons, Ltd.     

壁湍流猝发过程中速度分量的相位差对雷诺应力影响的实验研究

用IFA300恒温热线风速仪和×形二分量热线探针,以采样间隔小于最小湍流时间尺度的分辨率,精细测量了风洞中平板湍流边界层不同法向位置的瞬时流向、展向速度分量的时间序列信号.用子波分析辨识壁湍流相干结构猝发事件的能量最大准则,确定壁湍流相干结构猝发事件的时间尺度;用条件相位平均技术提取了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形,用互相关方法研究了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形的相位差关系及其对雷诺应力的影响,发现在缓冲层和对数律区,展向脉动速度与流向脉动速度的条件相位平均波形具有不同的相位;当两者相位基本一致时,雷诺应力达到正的最大值,此时湍流相干结构的产生非常活跃;当两者相位差分别集中在90°和270°附近时,雷诺应力的幅值减小并接近于零,此时湍流相干结构的产生和猝发都得到了抑制.     

EXPERIMENTAL STUDY OF MEASUREMENT FOR DISSIPATION RATE SCALING EXPONENT IN HEATED WALL TURBULENCE

Experimental investigations have been devoted to the study of scaling law of coarse-grained dissipation rate structure function for velocity and temperature fluctuation of non-isotropic and inhomogeneous turbulent flows at moderate Reynolds number. Much attention has been paid to the case of turbulent boundary layer, which is typically the non-istropic and inhomogeneous trubulence because of the dynamically important existence of organized coherent structure burst process in the near wall region . Longitudinal velocity and temperature have been measured at different vertical positions in turbulent boundary layer over a heated and unheated flat plate in a wind tunnel using hot wire anemometer. The influence of non-isotropy and inhomogeneity and heating the wall on the scaling law of the dissipation rate structure function is studied because of the existence of organized coherent structure burst process in the near wall region . The scaling law of coarse-grained dissipation rate structure function is foun     

用子波变换检测壁湍流信号局部标度指数

本文用子波变换检测了刻画壁湍流脉动信号自相似性的局部标度指数，研究了不同尺度的湍流结构的自相似性，发现在湍流边界层猝发过程中，喷射和扫掠发生时刻小尺度脉动速度信号的局部标度指数为负值，说明在大尺度猝发事件发生的时刻小尺度结构具有奇异的自相似性，在猝发过程中其作用不仅仅是对湍能的耗散．     

Study on local topology model of low/high streak structures in wall-bounded turbulence by tomographic time-resolved particle image velocimetry

The relationship between the bursting event and the low/high-speed streak in the logarithmic law (log-law) region of a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry (TRPIV) system is used to measure the instantaneous three-dimensional-three-component (3D-3C) velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.     

地下工程爆破振动信号能量分布特征的小波包分析

根据爆破振动信号具有短时非平稳的特点 ,利用小波包分析技术对地下工程爆破振动信号的能量分布特征进行了研究。首先 ,简略介绍了小波变换与小波包分析的特点 ;其次 ,基于MATLAB(MaterialsLab oratory)对段药量和爆源距离等不同条件下记录的 8条爆破振动信号进行小波包分析 ,得到了爆破振动信号在不同频带上的能量分布图 ;最后 ,分析了爆破振动信号能量的分布特征。本分析手段为研究地下工程爆破地震效应特别是振动速度 频率相关安全准则提供了一种有效的分析技术。