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| 1 | Phase-averaged waveforms of Reynolds stress in wall turbulence during the burst events of coherent structures显示文摘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. | JIANG Nan LIU Wei LIU JianHua TIAN Yan | 2008 | Science China(Physics,Mechanics & Astronomy)2008，51，7： | 20 |
| 2 | LINEAR INSTABILITY OF TURBULENT BOUNDARY LAYER AS A MECHANISM FOR THE GENERATION OF LARGE SCALE COHERENT STRUCTURES显示文摘I. BASIC IDEA Large eddies in the outer region of a turbulent boundary layer over a flat plate were found to have a mean streamwise extent of 2.5--3.0δ, where δ is the boundary layer thickness. Their convective velocity clusters around a value of 0.8U0, where U0 is the free stream velocity, and the period of their passage is roughly 3δ/U0. | 吴雪松 周恒 | 1989 | Chinese Science Bulletin1989，34，20： | 9 |
| 3 | The investigation of coherent structures in the wall region of a supersonic turbulent boundary layer based on DNS database显示文摘Through temporal mode direct numerical simulation, flow field database of a fully developed turbulent boundary layer on a flat plate with Mach number 4.5 and Reynolds number Reθ =1094 has been obtained. Commonly used detection meth- ods in experiments are applied to detecting coherent structures in the flow field, and it is found that coherent structures do exist in the wall region of a supersonic turbulent boundary layer. The detected results show that a low-speed streak is de- tected by using the Mu-level method, the rising parts of this streak are detected by using the second quadrant method, and the crossing regions from a low-speed streak to the high-speed one are detected by using the VITA method respectively. Notwithstanding that different regions are detected by different methods, they are all accompanied by quasi-stream-wise vortex structures. | HUANG ZhangFeng ZHOU Heng LUO JiSheng | 2007 | Science China(Physics,Mechanics & Astronomy)2007，50，3： | 8 |
| 4 | THE EFFECT OF COMPLIANT COATINGS ON COHERENT STRUCTURE IN TURBULENT BOUNDARY LAYERS显示文摘The velocity profile,turbulence intensity profile,streaky structure and bursting frequency in turbulentboundary layers over a flat plate with compliant coatings were investigated by Laser Doppler Anemometry and condi-tional sampling techniques.This experiment led to the conclusions that in boundary layer flows on a compliantwall,as compared with that on a rigid wall,the log law region was extended further away from the wall,and thatthe maximum value of each turbulence intensity profile in the near wall region was reduced and the bursting frequencyobviously decreased with the compliant coatings.One point worthy of notice was that the above results were verymuch like those of polymer drag reduction experiments. | Shu Wei Liu Weiming (Tianjin University) | 1990 | Acta Mechanica Sinica1990，6，2： | 7 |
| 5 | Large-eddy simulations and vortex structures of turbulent jets in crossflow显示文摘Using the method of large-eddy simulation, the 3-dimensional turbulent jets in crossflow with stream-wise and transverse arrangements of nozzle are simulated, emphasizing on the dynamical process of generation and evolution of vortex structures in these flows. The results show that the basic vortex structures in literatures, such as the counter-rotating vortex pair, leading-edge vortices, lee-side vortices, hanging vortices, kidney vortices and anti-kidney vortices, are not independent physical substances, but local structures of the basic vortex structure of turbulent jets in crossflow-the 3-D stretching vortex rings originating from the orifice of the nozzle, which is discovered in this study. Therefore, the most important large-scale structures of turbulent jets in crossflow are unified to the 3-D vortex rings which stretch and twist in stream-wise and swing in transverse directions. We also found that the shedding frequencies of vortex rings are much lower than the one corresponding to the appearance of leading-edge and lee-side vortices in the turbulent jets. | GUAN Hui1,2 & WU ChuiJie2 1 School of Mechanical and Power Engineering,East China University of Science and Technology,Shanghai 200237,China 2 Research Center for Fluid Dynamics,PLA University of Science and Technology,Nanjing 211101,China | 2007 | Science China(Physics,Mechanics & Astronomy)2007，50，1： | 5 |
| 6 | The mechanism for the generation of coherent structures in the wall region of a turbulent boundary layer显示文摘By using the idea of resonant triad of the theory of hydrodynamic stability, a theoretical model was proposed for the generation of the coherent structures in the wall region of a turbulent boundary layer. The obtained structural configuration, the spanwise length scale and the convective speed of the coherent structures are in agreement with those obtained by numerical simulations. To further characterize these structures, the probability density distribution of the non-dimensional circulation difference of the largely unsymmetric streamwise vortex pairs has been calculated. Its comparison with those obtained by the numerical simulations is in general satisfactory. | 周恒 熊忠民 | 1995 | Science China Mathematics1995，38，2： | 5 |
| 7 | INTERACTIVE STUDY BETWEEN IDENTICAL COHERENT STRUCTURES IN THE WALL REGION OF A TURBULENT BOUNDARY LAYER显示文摘A theoretical model for identica l coherent structures in the wall region of a turbulent boundary layer was propo sed, using the idea of general resonant triad of the hydrodynamic stability. The evolution of the structures in the wall region of a turbulent boundary layer wa s studied by combining the compact finite differences of high numerical accuracy and the Fourier spectral hybrid method for solving the three dimensional Navier -Stokes equations. In this method, the third order mixed explicit-implicit sch eme was applied for the time integration. The fifth-order upwind compact finite difference schemes for the nonlinear convection terms in the physical space, an d the sixth-order center compact schemes for the derivatives in spectral space were introduced, respectively. The fourth-order compact schemes satisfied by th e velocities and pressure in spectral space was derived. As an application, the method was implemented to the wall region of a turbulent boundary to study the e volution of identical coherent structures. It is found that the numerical result s are satisfactory. | Lu Chang-gen (College of water Resources and Environment, Hohai University, Nan jing 210098, China) | 2002 | Journal of Hydrodynamics2002，14，1： | 4 |
| 8 | WAVELET ANALYSIS OF COHERENT STRUCTURES IN A THREE-DIMENSIONAL MIXING LAYER显示文摘Wavelet analysis is applied to the results obtained by the direct nu-merical simulation of a three-dimensional (3D) mixing layer in order to investigatecoherent structures in dimension of scale. First, 3D orthonormal wavelet bases areconstructed, and the corresponding decomposition algorithm is developed. Then theNavier-Stokes equations are transformed into the wavelet space and the architecturefor multi-scale analysis is established. From this architecture, the coarse field imagesin different scales are obtained and some local statistical quantities are calculated.The results show that, with the development of a mixing layer, the energy spectrumdensities for different wavenumbers increase and the energy is transferred from theaverage flow to vortex structures in different scales. Due to the non-linear interactionsbetween different scales, cascade processes of energy are very complex. Because vor-tices always roll and pair at special areas, for a definite scale, the energy is obtainedfrom other scales at some areas while it is transferred to other scales at other areas.In addition, energy dissipation and transfer always occur where an intense interactionbetween vortices exists. | 林建忠 邵雪明 倪利民 | 2002 | Acta Mechanica Sinica2002，18，1： | 4 |
| 9 | THE LOSS OF STABILITY OF LAMINAR FLOW IN OPEN CHANNEL AND THE MECHANISM OF SAND RIPPLE FORMATION显示文摘In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance, such a phenomenon is called the 'detection property' of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly. | BAI Yu-chuan(白玉川) LUO Ji-shen(罗纪生) | 2002 | Applied Mathematics and Mechanics(English Edition)2002，23，3： | 4 |
| 10 | A KIND OF FAST CHANGING COHERENT STRUCTURE IN A TURBULENT BOUNDARY LAYER显示文摘Coherent structures of a turbulent boundary layer were investigatedby hydrogen bubble method.A kind of fast changing structure was observed.Thatis a spot in which all the hydrogen bubbles vanish much faster than in other regions.This investigation verified that dark-spot is formed by a strong sweep from outerlayer.Inside a dark-spot the local instantaneous flow speed might be four times ofits neighboring high-speed streaks.Comparing with the low/high speed streaks,bothdark-spot and the vortical structures around it are changing very fast.Around dark-spot intensive shear layers are formed and indications of the generation of small-scalestructures could be observed. | 连淇祥 | 1999 | Acta Mechanica Sinica1999，15，3： | 4 |
| 11 | Coherent structures and wavepackets in subsonic transitional turbulent jets显示文摘A large eddy simulation(LES) is performed for two subsonic jets with a Reynolds number of Re = 105,which have different core temperatures, i.e., the cold and hot jet. The far-field overall sound pressure levels(OASPL)and noise spectra are well validated against previous experimental results. It is found that the OASPL is raised by heating at shallow angles. The most energetic coherent structures are extracted with specified frequencies using the filter based on the frequency domain variant of the snapshot method of proper orthogonal decomposition(POD). The m = 0, 1 modes have high coherence of near-field pressure for both jets, while the coherence of m = 0 modes is enhanced greatly by heating. Based on the coherent structures, spatial wavepackets are educed and the characteristics of growth, saturation and decay are analyzed and compared between the two jets in detail. The results show that heating would enhance the linear growth rate for high frequency components, and nonlinear growth rates for low frequency components in general, which are responsible for higher OASPL in the hot jet. The far-field sound generated by wavepackets is computed using the Kirchhoff extrapolation,which matches well with that of LES at shallow angles.This indicates that the wavepackets associated with coherent structures are dominant sound sources in forced transitional turbulent jets. Additionally, the present POD method is proven to be a robust tool to extract the salient features of the wavepackets in turbulent flows. | Haihua Yang Xingchen Zhang Lingke Ran Dejun Sun Zhenhua Wan | 2017 | Acta Mechanica Sinica2017，33，1： | 4 |
| 12 | Analysis of flow structures in supersonic plane mixing layers using the POD method显示文摘The proper orthogonal decomposition(POD) method was applied to analyzing the database obtained from the direct numerical simulation(DNS) of supersonic plane mixing layers.The effect of different forms of the inner products in the POD method was investigated.It was observed that the mean flow contributes to a predominant part of the total flow energy,and the energy spectrum of the turbulence fluctuations covers a wide range of POD modes.The patterns of leading(high energy) POD modes reveal that the flow structures exhibit spanwise counter rotating rolls,as well as oblique vortices.These flow patterns are insensitive to the velocity of the observer.As the convective Mach number increases,the energy spectrum be-comes wider,the leading POD modes contain more complicated structures,and the flow becomes more chaotic. | YANG Qin FU Song | 2008 | Science China(Physics,Mechanics & Astronomy)2008，51，5： | 4 |
| 13 | Study on macro-instability in stirred tank显示文摘Macro-instability(MI)is an important natural phenomenon affecting the mixing performance in stirred tank significantly,which results from movement and evolution of large eddies.Factors associated with MI frequency in mixing operation and energy dissipation related to MI were reviewed.Flow pattern in turbulent regime contains many coherent structures,which have much energy vortices and may result in flow field MI.Adjustment of coherent structure and controlling MI may contribute to energy saving and good mixing performance.Controlling methods for MI was prospected. | 刘作华 陶长元 宁伟征 孙瑞祥 | 2010 | 化工进展2010，29，S1： | 3 |
| 14 | Effect of pressure gradient on coherent structures in a turbulent boundary layer显示文摘By using the idea of resonant triad of the theory of hydrodynamic stability, the effect of pressure gradient on coherent structures in a turbulent boundary layer is investigated. The favorable pressure gradient suppresses the generation of the coherent structure, while the adverse pressure gradient has the opposite effect. The scale, form, as well as the propagation speed of the coherent structures are different from those with zero pressure gradient. The theoretical results are, in general, m agreement with those found from experiments. From the calculated probability density curve of the circulation differences of the nearly streamwise vortex pairs, it is found that the adverse pressure gradient makes the vortex pair more symmetric. | 周恒 陆利蓬 | 1997 | Science China Mathematics1997，40，4： | 2 |
| 15 | Study of formation boundary and dip attribute extraction based on edge detection technology显示文摘In the seismic profile interpretation process,as the seismic data are big and the small geological features are difficult to identify,improvement of the efficiency is needed. In this study,structure tensor method in computer image edge detection processing is applied into the 2D seismic profile. Coherent attribute is used to extract formation edge. At the same time,extracting the eigenvalues and eigenvectors to calculate the seismic geometric properties which include dip and apparent dip,automatic identification is achieved. Testing the Gaussian kernel function with synthetic models and comparing the coherent attribute and dip attribute extraction results before and after,the conclusion that Gaussian filter can remove the random noise is obtained. | WANG Yanbo SUN Jianguo SONG Chao | 2016 | Global Geology2016，19，2： | 2 |
| 16 | Inflows/outflows driven particle dynamics in an idealised lake显示文摘This paper considers fluid mixing driven by inflows connected to a circular shallow lake using a numerical framework consisting of a shallow water hydrodynamic model and a passive particle-tracking model.With the flow field driven by alternate inflows predicted by a shallow water model,particle trajectories are traced out using a particle tracking model.The horizontal fluid mixing dynamics are then interpreted using dynamics system analysis approaches including finite-time Lyapunov exponent(FTLE)and Lagrangian coherent structure(LCS).From the simulation results,it is confirmed that periodic inflows are able to create a weak dynamic system in an idealised circular lake,with the particle dynamics controlled by a single dimensionless parameter associated with the inflow duration.The mixing and transport property of the lake changes from regular to chaotic as the value of the dimensionless parameter increases until global chaotic particle dynamics is achieved.By further analysing the advection of particles injected continuously to the inflows(freshwater),the fate of“freshwater”particles in a“polluted”lake is tracked and revealed.The results provide useful guidance for engineering applications,i.e.,transferring freshwater from rivers to improve the water quality in polluted water bodies such as lakes.The presented approach will be able to facilitate the design of‘optimised’schemes for such engineering implementation. | Cheng-hua Dang Jingchun Wang Qiuhua Liang | 2019 | Journal of Hydrodynamics2019，31，5： | 2 |
| 17 | SOME CHARACTERISTICS OF LOW-SPEED STREAKS UNDER SHEARED AIR-WATER INTERFACES显示文摘The characteristics of low-speed fluid streaks occurring under shearedair-water interfaces were examined by means of hydrogen bubble visualization tech-nique.A critical shear condition under which the streaky structure first appears wasdetermined to be u_r≈0.19 cm/s.The mean spanwise streak spacing increases withdistance from the water surface owing to merging and bursting processes,and a lin-ear relationship describing variation of non-dimensional spacing (?) versus y^+ wasfound essentially independent of shear stress on the interface.Values of (?),however,are remarkably smaller than their counterparts in the near-wall region of turbulentboundary layers.Though low-speed streaks occur randomly in time and space,thestreak spacing exhibits a lognormal probability distribution behavior.A tentativeexplanation concerning the formation of streaky structure is suggested,and the factthat (?) takes rather smaller values than that in wall turbulence is briefly discussed. | 王双峰 贾复 | 2001 | Acta Mechanica Sinica2001，17，2： | 2 |
| 18 | The visualization of turbulent coherent structure in open channel flow显示文摘Due to its multiscale and multi-layer natures,the coherent structures of turbulent in the open channel flow is complex and difficult to be visualized for understanding its evolution.In this paper,five types of methods for the vortical structure in the fluids,namely the Q-criterion,the vorticity,the Omega method,the velocity-vorticity correlation structures(VVCS)as well as the most recent Rortex method,are adopted to visualize the turbulent flow in the open channel.With the free surface modelled as a free slip boundary,a direct numerical simulation(DNS)is carried out to study the multi-layered flow structure characteristics under the free surface.The visualization results by the Q-criterion,the vorticity,the Omega method and the Rortex are firstly analyzed.Then the turbulent flow layers near the free surface are identified with corresponding anisotropy indices.Afterwards,the VVCS within various turbulence layers are visualized accordingly.This research indicates that the VVCS can straightforwardly show the geometry information of the cohere nt structures of turbulent in different layers for the ope n channel flow. | Xiao-dong Bai Wei Zhang Qing-he Fang Yong Wang Jin-hai Zheng An-xin Guo | 2019 | Journal of Hydrodynamics2019，31，2： | 2 |
| 19 | Experimental Studies of Two-Phase Round Turbulent Jet Coherent Structures显示文摘Coherent structures of a two\|phase round turbulent jet have been studied experimentally. The flow profiles at different Reynold’s numbers and various positions from the jet exit are visualized using a sheet laser source. The jets include two types,an air jet laden with incense smoke and an air jet laden with two kinds of solid particles, glass beads and catalytic cracking beads. The developments of both the large eddy structures of the round turbulent jet and the local particle dispersion in the vortex structures were recorded with a high\|speed movie camera. Free and excited jet conditions were tested. Analysis of the video pictures suggests a critical intrinsic frequency exists in the helical coherent structures of the air phase. In the spectral space the clockwise and counter\|clockwise helical structures occupy different positions. Large scale structures exsit in the two\|phase jet. The patterns are similar to those of the air jet with the Stokes numbers in the range of 1-8 32. | 范全林 张会强 郭印诚 王希麟 林文漪 | 2000 | Tsinghua Science and Technology2000，5，1： | 2 |
| 20 | Numerical simulation of coherent structure in two-dimensional compressible mixing layers显示文摘The coherent structure in two-dimensional mixing layers is simulated numerically with the compressible Navier-Stokes equations. The Navier-Stokes equations are discretized with high-order accurate upwind compact schemes. The process of development of flow structure is presented: loss of stability, development of Kelvin-Helmholtz instability, rolling up and pairing. The time and space development of the plane mixing layer and influence of the compressibility are investigated. | 傅德薰 马延文 | 1996 | Science China Mathematics1996，39，11： | 2 |
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