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Impact of depth ratio on flow structure and turbulence characteristics of compound open channel flows

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Water Science and Engineering 2022年第3期15卷 265-272页

作者： Shao-wei Ding Cheng Zeng Jie Zhou Ling-ling Wang Chen Chen College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China College of Mechanics and Materials Hohai UniversityNanjing 211100China

Compound open channel flows appear in most natural rivers are of great importance in river management and flood *** this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical *** depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and *** instantaneous coherent structures were presented by the Q criterion *** impact of hr on flow structure and turbulence charac-teristics was *** results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.

关键词： Large eddy simulation Compound open channel Depth ratio Flow structure turbulence characteristics

turbulence characteristics of Swirling Reacting Flow in a Combustor with Staged Air Injection

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Chinese Journal of Chemical Engineering 2006年第5期14卷 634-641页

作者：张健普勇周力行 Department of Engineering Mechanics Tsinghua University

This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secon-dary non-swirling jet. A three dimension-laser particle dynamic analyzer (PDA) was employed to measure the in-stantaneous gas velocity. The probability density functions (PDF) for the instantaneous gas axial and tangential ve-locities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are ob-tained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion.

关键词： swirling reacting flow staged combustion turbulence characteristics

Eddy Covariance Tilt Corrections over a Coastal Mountain Area in South-east China:Significance for Near-Surface turbulence characteristics

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Advances in Atmospheric Sciences 2012年第6期29卷 1264-1278页

作者：刘丽王体健孙振海王勤耕庄炳亮韩永李树 School of Atmospheric Sciences Nanjing University Guizhou Key Laboratory of Mountainous Climate and Resources Institute of Microorganism Epidemic Academy of Military Medical Sciences School of Environment Nanjing University

turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation： double rotation （DR）, triple rotation （TR）, and classic planar-fit rotation （PF） were examined in terms of correction of eddy covariance flux. Using the commonly used DR and TR methods, unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics. The PF method rotates the coordinate system to an ensemble-averaged plane, and shows large tilt error due to an inaccurate fit plane over variable terrain slopes. In this paper, we propose another coordinate rotation scheme. The observational data were separated into two groups according to wind direction. The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s-1. Then, the coordinate systems were rotated to their respective best- fit planes for all available hourly observations. We call this the PF10 method. The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics, the spectra of wind-velocity components, and sensible heat and momentum fluxes under various atmospheric stabilities. Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality. The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes.

关键词： complex terrain atmospheric surface layer eddy covariance method tilt correction turbulence characteristics flux-variance similarity

Aero-Hydrodynamic Coupled Dynamic characteristics of Semi-Submersible Floating Offshore Wind Turbines Under Inflow turbulence

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中国海洋工程:英文版 2023年第4期37卷 660-672页

作者： JIANG Hai-rui BAI Xing-lan Murilo A.VAZ School of Naval Architecture and Maritime Zhejiang Ocean UniversityZhoushan 316022China Key Laboratory of Offshore Engineering Technology of Zhejiang Province Zhoushan 316022China Ocean Engineering Program Federal University of Rio de JaneiroRio de JaneiroBrazil

In this study,the frequency characteristics of the turbulent wind and the effects of wind-wave coupling on the low-and high-frequency responses of semi-submersible floating offshore wind turbines(FOWT)are *** wave load components,such as first-order wave loads,combined first-and second-order difference-frequency wave loads,combined first-and second-order sum-frequency wave loads,and first-and complete second-order wave loads are taken into consideration,while different turbulent environments are considered in aerodynamic *** com-parison is based on time histories and frequency spectra of platform motions and structural load responses and statistical *** findings indicate that the second-order difference-frequency wave loads will significantly increase the natural frequency of low-frequency motion in the responses of the platform motion and structure load of the semi-submersible platform,which will cause structural fatigue *** the action of turbulent wind,the influences of second-order wave loads on the platform motion and structural load response cannot be ignored,especially under extreme sea ***,in order to evaluate the dynamic responses of semi-submersible FOWT more accurately,the actual environment should be simulated more realistically.

关键词： turbulence characteristics floating offshore wind turbines second-order hydrodynamic loads low-and high-frequency responses aero-hydrodynamic coupling

Particle effects on the hydrodynamics in slurry bubble column reactors:A review from multiscale mechanisms Author links open overlay panel

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Particuology 2024年第8期91卷 176-189页

作者： Min An Jingqi Gao Tiankuo Wang Xiangnan Li National Supercomputing Center in Zhengzhou Zhengzhou UniversityZhengzhou450001China School of Chemical Engineering and New Energy Xiamen University MalaysiaSepangSelangor43900Malaysia School of Chemistry and Chemical Engineering Henan Normal UniversityXinxiang453007China

Particles can appear as catalyst,reactant or product in various gas-liquid-solid three-phase production *** bubble column reactors(SBCRs),as a kind of three-phase reactors,are preferred for phase contacting and ***,literature studies concerning the effects of particles on the hydrodynamics of SBCRs are manifold and inconsistent in ***,the multiscale interactions between particles,turbulent eddies and bubbles determine the reactor *** review focuses on revealing the particle effects in SBCRs from the perspective of multiscale *** hydrodynamic changes due to particle effects in literature are *** parameters,including the Stokes number,the solid-to-liquid density ratio,the ratio of particle and liquid characteristic lengths,the contact angle and the particle volume fraction are adopted to evaluate the characteristics of gas-liquid-solid *** relationships between particle influencing mechanisms and these parameters are analyzed and *** experimental results are explained by different ranges of these dimensionless ***,particle effects at the mesoscale and microscale,such as the influence on the bubble dynamics and the pivoting effect on the turbulence energy spectrum,are ***,progress in modeling the SBCRs with consideration of particles effects using the Euler method are *** review aims to improve the overall understanding of the complex hydrodynamics in the SBCRs.

关键词： Slurry bubble column reactors Particle effects turbulence characteristics Bubble dynamics CFD

Development of a fan-stirred constant volume combustion chamber and turbulence measurement with PIV

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Frontiers in Energy 2022年第6期16卷 973-987页

作者： Haoran ZHAO Jinhua WANG Xiao CAI Zhijian BIAN Hongchao DAI Zuohua HUANG State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

A fan-stirred combustion chamber is developed for spherically expanding flames,with P and T up to 10 bar and 473 K,*** characteristics are estimated using particle image velocimetry(PIV)at different initial pressures(P=0.5-5 bar),fan frequencies(ω=0-2000 r/min),and impeller diameters(D=100 and 114 mm).The flame propagation of methanol/air is investigated at different turbulence intensities(u′=0-1.77 m/s)and equivalence ratios(f=0.7-1.5).The results show that u′is independent of P and proportional toω,which can be up to 3.5 m/s at 2000 r/min.L_(T)is independent of P and performs a power regression withω*** turbulent field is homogeneous and isotropic in the central region of the chamber while the inertial subrange of spatial energy spectrum is more collapsed to-5/3 law at a high Re_(T).Compared to laminar expanding flames,the morphology of turbulent expanding flames is wrinkled and the wrinkles will be finer with the growth of turbulence intensity,consistent with the decline of the Taylor scale and the Kolmogorov *** determined S_(L)in the present study is in good agreement with that of previous *** S_(L)and S_(T)of methanol/air have a non-monotonic trend with f while peak S_(T)is shifted to the richer side compared to S_(L).This indicates that the newly built turbulent combustion chamber is reliable for further experimental study.

关键词： fan-stirred combustion chamber turbulence characteristics particle image velocimetry(PIV) methanol turbulent expanding flames

Analysis of atmospheric turbulence in the upper layers of sea fog

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Chinese Journal of Oceanology and Limnology 2015年第3期33卷 809-818页

作者：李永平郑运霞 Shanghai Typhoon Institute China Meteorological Administration

Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.

关键词： ultrasonic anemometers turbulence characteristics momentum flux sensible heat flux variation in sea fog

FLOW STRUCTURE OF PARTLY VEGETATED OPEN-CHANNEL FLOWS WITH EELGRASS

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Journal of Hydrodynamics 2009年第3期21卷 301-307页

作者： WANG Chao YU Ji-yu WANG Pei-fang GUO Peng-cheng Key Laboratory of Integrated Regulation and Resource Department on Shallow Lakes Ministry of Education Hohai University Nanjing 210098 China State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Nanjing 210098 China College of Environmental Science and Engineering Hohai University Nanjing 210098 China Yellow River Engineering Consulting Co. Ltd. Zhengzhou 450003 China

Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter （ADV）. We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions： inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents （a relatively minor flow superimposed on the primary flow, with significantly different speed and direction）, generated by the anisotropy of the turbulence.

关键词： open channel aquatic vegetation velocity profile turbulence characteristics

Experimental study of the flow structure of decelerating and accelerating flows under a gradually varying flume

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Journal of Hydrodynamics 2015年第3期27卷 340-349页

作者：王协康易子靖闫旭峰黄尔刘兴年 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Department of Civil and Structural Engineering The Hong Kong Polytechnic University

The turbulence characteristics of both decelerating and accelerating flows under a gradually varying flume are investigated by using a three-dimensional down-looking acoustic Doppler velocimeter （ADV）. The time-averaged velocity profiles are flatened except for the central parts, and fairly fit into logarithmic laws and those in the plane circulation under the gradual expansion are more likely to be negative. The complex secondary currents are identified under the present gradual transition attributed to the combination of driving forces induced by both the boundary configuration variation and the tmbalanced turbulence： a circulation on each side of the expansion and a pair of circulations on each side of the contraction. One sees an anisotropy in the turbulence intensities, the turbulence intensities increase or level out with the flow depth except those under expansion, and the V component of the turbulence intensity typically outweighs that in the streamwise direction. Apart from the above results, the respective particular distributions of the primary Reynolds shear stresses （ rxy and rxz ） under the gradual expansion and contraction can account for the patterns of the secondary currents in this investigation.

关键词： turbulence characteristics secondary currents gradual transition non-uniform flows open channel