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Tomographic PIV investigation of coherent structures in a turbulent boundary layer flow

Acta Mechanica Sinica 2012年第3期28卷 572-582页

作者： zhan-qi tang Nan Jiang Andreas Schroder Reinhard Geisler Department of Mechanics Tianjin University300072 TianjinChina Tianjin Key Laboratory of Modern Engineering Mechanics 300072 TianjinChina Institute of Aerodynamics and Flow Technology Department of Experimental MethodsBunsenstrasse 1037073 GiSttingenGermany

Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional co- herent structures in the logarithmic region of the turbulent boundary layer in a water tunnel. The Reynolds number based on momentum thickness is Reo = 2 460. The in- stantaneous velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low speed fluid, which is flanked on either side by high- speed ones. Statistical support for the existence of hairpins is given by conditional averaged eddy within an increasing spanwise width as the distance from the wall increases, and the main vortex characteristic in different wall-normal re- gions can be reflected by comparing the proportion of ejec- tion and its contribution to Reynolds stress with that of sweep event. The pre-multiplied power spectra and two-point cor- relations indicate the presence of large-scale motions in the boundary layer, which are consistent with what have been termed very large scale motions （VLSMs）. The three dimen-sional spatial correlations of three components of veloc- ity further indicate that the elongated low-speed and high- speed regions will be accompanied by a counter-rotating roll modes, as the statistical imprint of hairpin packet structures, all of which together make up the characteristic of coherent structures in the logarithmic region of the turbulent boundary layer （TBL）.

关键词： Tomographic particle image velocimetry Tur-bulent boundary layer Coherent structures Hairpin vortex Very large scale motion

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Drag reduction and hairpin packets of the turbulent boundary layer over the superhydrophobic-riblets surface

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Journal of Hydrodynamics 2021年第3期33卷 621-635页

作者： Xin-wei Wang Zi-ye Fan zhan-qi tang Nan Jiang School of Mechanical Engineering Tianjin UniversityTianjin300354China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin300354China

This paper presents experimental measurements by the time-resolved particle image velocimetry(TR-PIV)for the turbulent boundary layer(TBL)over the smooth surface,the superhydrophobic(SH)surface,and the superhydrophobic-riblets(SR)surface in an open-surface recirculating water *** Reynolds number based on the wall friction velocity and the thickness of the TBL over the smooth surface is *** SH surface and the SR surface are manufactured by the laser texturing method on the smooth surface and the riblets surface,*** employing the(modified)Clauser method,a superior efficacy of the drag reduction of about 22.1%is obtained on the SR surface,while the drag reduction rate for the SH surface is about 18.7%.Comparing with the SH surface,the declining 2-order statistics in the near-wall region also indicates a significant drag reduction over the SR *** large-scale structure components extracted by the proper orthogonal decomposition are found to generate a majority of the Reynolds shear stress in the region y^(+)>*** strength of the large-scale features over the rough surfaces(SH and SR surfaces)at disparate wall-normal positions is visualized by the Quadrant splitting method and the conditional *** appearance of the large-scale structures such as the hairpin packets characterized by the two-point correlation shows an excellent consistency with the statistics *** hairpin packets over the SH surface seem always smaller and weaker than those over the smooth *** the SR surface,the hairpin packets in the region 0.1≤y/δ<0.3 are the smallest and weakest among those over the three surfaces,while the scale and the strength of the hairpin packets exceed those over the smooth surface in the region 0.3

关键词： Turbulent boundary layer superhydrophobic riblets drag reduction hairpin packets

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Effect of high-or low-speed fluctuations on the small-scale bursting events in an active control experiment

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Chinese Physics B 2021年第1期30卷 319-327页

作者： Xiao-Tong Cui Nan Jiang zhan-qi tang Department of Mechanics Tianjin UniversityTianjin 300354China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin 300354China

Active control of a fully developed turbulence boundary layer(TBL) over a flat plate has been investigated with a statistical view. The piezoelectric(PZT) oscillator is employed to produce periodic input into the inner region of the TBL.A wall probe is fixed upstream of the oscillator to identify the high-or low-speed fluctuations as the detecting ***, the impact of the detecting signals on the small-scale bursting process is investigated based on the data acquired by the traversing probe downstream of the oscillator. The results indicate that the small-scale bursting intensity is restrained more apparently at high-speed detecting fluctuations but less impacted at low-speed detecting fluctuations. Furthermore, the perturbed-scale fluctuations arrange the small-scale bursting process in the near-wall region. The detecting signals have an obvious impact on this arrangement, especially the high-intensity regions of the small-scale bursting events: the vibration enhances the intensity at high-speed detecting signals but weakens it at low-speed detecting signals in these regions, which gives a direct evidence on how detecting signals interfering the small-scale bursting process.

关键词： turbulent boundary layer active control discrete wavelet decomposition small-scale bursting process

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Experimental investigation of wall-bounded turbulence drag reduction by active control of double piezoelectric vibrator

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Journal of Hydrodynamics 2020年第4期32卷 747-757页

作者： Jian-xia Bai Yong-xiang Huang Nan Jiang Xing-yu Ma zhan-qi tang Department of Mechanics School of Mechanical EngineeringTianjin UniversityTianjin 300354China Department of Mathematics Tianjin University Renai CollegeTianjin 301636China State Key Laboratory of Marine Environmental Science College of Ocean and Earth SciencesXiamen UniversityXiamen 361102China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin 300354China

In order to manipulate the large-scale coherent structures in the wall-bounded turbulence and reduce the skin-friction,an active-control experimental investigation is performed by using the synchronous and asynchronous vibrations of double piezoelectric vibrators embedded spanwisely on a smooth flat plate surface.A TSI-IFA300 hot-wire anemometer and a TSI-1621 A-Tl.5 hot-wire probe are used to measure the time series of the instantaneous velocity at different *** influences of the vibrations on the wall-bounded turbulence are compared in a multi-scale point of view.A disturbance Reynolds Number Red=pd2 f/μis introduced to represent the disturbance.A probability density functions(PDFs)of the multi-scale components of the turbulence velocity and the multi-scale conditional phase-averaged waveform are studied in detail using the wavelet *** results show that the maximum drag reduction rate 18.54%is obtained at 100 V/160 Hz and Red=0.54 in the asynchronous vibration *** disturbances generated by the vibrators have a significant influence on the sweep events of the *** asynchronous vibration model is more effective than the synchronous vibration one.A possible physical mechanism is suggested to explain why the disturbance frequency of 160 Hz leads to an optimal parameter set for the drag reduction.

关键词： Wall-bounded turbulence active control drag reduction piezoelectric vibrator multi-scale analysis conditional phase-averaged wavefonns coherent structure

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Effects of the superhydrophobic surface on coherent structures in the turbulent boundary layer

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Acta Mechanica Sinica 2022年第10期38卷 66-79页

作者： Yu-Fei Wang Xin-Wei Wang Xing-Yu Ma zhan-qi tang Nan Jiang School of Mechanical Engineering Tianjin UniversityTianjin300354China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin300354China

The influence of drag-reducing superhydrophobic(SHPo)surface on turbulent boundary layer(TBL)is investigated.A large area of the SHPo surface(about 10δ99 in the streamwise and 5δ99 in the spanwise)is fabricated to fully evolve the coherent structures in the TBL.A comparative experiment is carried out by time-resolved particle image velocimetry on a smooth surface and the SHPo surface at Re_(τ)=*** profiles with high spatial resolution are obtained by the single-pixel resolution ensemble correlation *** reduction of the streamwise velocity gradient is observed in the near-wall region of y<0.05δ99 on the SHPo *** comparing the turbulence statistics,it is discovered that the Reynolds shear stress is reduced by 15.7%,and the turbulent kinetic energy is reduced by 12.3%on the SHPo *** coherent structures are investigated by the snapshot proper orthogonal decomposition(POD)and conditional average *** intensity of Q_(2)/Q_(4)events on the SHPo surface has declined by 16.1%and 12.7%,*** number of clockwise spanwise vortices is substantially reduced by 47%.Through spatial two-point correlation analysis,the streamwise and wall-normal direction scales of the coherent structures on the SHPo surface are suppressed.

关键词： Superhydrophobic Turbulence Coherent structure

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Active control of wall-bounded turbulence for drag reduction with piezoelectric oscillators

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Chinese Physics B 2018年第7期27卷 397-403页

作者： Jian-Xia Bai Nan Jiang Xiao-Bo Zheng zhan-qi tang Kang-Jun Wang Xiao-Tong Cui Department of Mechanics School of Mechanical EngineeringTianjin UniversityTianjin 300350China Deptartment of Mathematics Tianjin University Renal CollegeTianfin 301636China Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin 300072China

An experimental investigation was performed for active control of coherent structure bursting in the near-wall region of the turbulent boundary layer. By means of synchronous and asynchronous vibrations with double piezoelectric vibrators, the influence of periodic vibration of the double piezoelectric vibrators on the mean velocity profile, drag reduction rate, and coherent structure bursting is analyzed at Reo = 2766. The case with 100 V/160 Hz-ASYN is superior to other conditions in the experiment and a relative drag reduction rate of 18.54% is exciting. Asynchronous vibration is more effective than synchronous vibration in drag reduction at the same voltage and frequency. In all controlled cases, coherent structures at large scales are regulated while the small-scale structures are stimulated. The fluctuating velocity increases significantly. A periodic regulating effect on the coherent structure can be seen in the ASYN control conditions at the frequency of 160 Hz.

关键词： turbulent boundary layer active control double piezoelectric vibrators

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Potential role of tanycyte-derived neurogenesis in Alzheimer's disease

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Neural Regeneration Research 2025年第6期20卷 1599-1612页

作者： Guibo qi Han tang Jianian Hu Siying Kang Song qin Department of Anatomy Histologyand EmbryologySchool of Basic Medical SciencesFudan UniversityShanghaiChina State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science Fudan UniversityShanghaiChina

Tanycytes, specialized ependymal cells located in the hypothalamus, play a crucial role in the generation of new neurons that contribute to the neural circuits responsible for regulating the systemic energy balance. The precise coordination of the gene networks controlling neurogenesis in naive and mature tanycytes is essential for maintaining homeostasis in adulthood. However, our understanding of the molecular mechanisms and signaling pathways that govern the proliferation and differentiation of tanycytes into neurons remains limited. This article aims to review the recent advancements in research into the mechanisms and functions of tanycyte-derived neurogenesis. Studies employing lineage-tracing techniques have revealed that the neurogenesis specifically originating from tanycytes in the hypothalamus has a compensatory role in neuronal loss and helps maintain energy homeostasis during metabolic diseases. Intriguingly,metabolic disorders are considered early biomarkers of Alzheimer's disease. Furthermore,the neurogenic potential of tanycytes and the state of newborn neurons derived from tanycytes heavily depend on the maintenance of mild microenvironments, which may be disrupted in Alzheimer's disease due to the impaired blood–brain barrier ***, the specific alterations and regulatory mechanisms governing tanycyte-derived neurogenesis in Alzheimer's disease remain unclear. Accumulating evidence suggests that tanycyte-derived neurogenesis might be impaired in Alzheimer's disease, exacerbating neurodegeneration. Confirming this hypothesis, however, poses a challenge because of the lack of long-term tracing and nucleus-specific analyses of newborn neurons in the hypothalamus of patients with Alzheimer's disease. Further research into the molecular mechanisms underlying tanycyte-derived neurogenesis holds promise for identifying small molecules capable of restoring tanycyte proliferation in neurodegenerative diseases. This line of investigation could pro

关键词： Alzheimer's disease blood–brain barrier ependymoglial cells hypothalamus metabolic diseases neural stem cells neurogenesis neuroinflammatory diseases neurons tanycyte

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新生报到管理系统的设计与实现

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电脑知识与技术 2008年第12期3卷 1551-1554页

作者：王学玲綦占堂中国海洋大学青岛学院信息工程系山东青岛266300

选用Dreamweaver作为系统的前端开发平台、IIS组件作为Web服务器，ASP＋SQL Server的技术方案。该系统克服了传统人工报到的缺点，与其他报到管理软件相比，又具有成本低、运行时占用系统资源小、通用性强、维护方便、扩展性好等优势。

关键词：新生报到管理系统 ASP技术 SQL数据库

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Staged dendrite suppression for high safe and stable lithium-sulfur batteries

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Journal of Energy Chemistry 2025年第1期100卷 674-683页

作者： Jun Jiang Zhenjie Lu Yanwen Ding Shujun Liu Zhijie qi Tian tang Yunfan zhang Zhiyuan Ma Jingwen Sun Liang Xue Wenyao zhang Pan Xiong Xin Wang Junwu Zhu Yongsheng Fu Key Laboratory for Soft Chemistry and Functional Materials of Ministry of Education Nanjing University of Science and Technology Jiangsu Pylon Battery Co.Ltd

The unavoidable dendrite growth and shuttle effect have long been stranglehold challenges limiting the safety and practicality of lithium-sulfur ***,we propose a dual-action strategy to address the lithium dendrite issue in stages by constructing a multifunctional surface-negatively-charged nanodiamond layer with high ductility and robust puncture resistance on polypropylene （PP） *** uniformly loaded compact negative layer can not only significantly enhance electron transmission efficiency and promote uniform lithium deposition,but also reduce the formation of dendrite during early deposition *** importantly,under the strong puncture stress encountered during the deterioration of lithium dendrite growth under limiting current,the high ductility and robust puncture resistance（145.88 MPa） of as-obtained nanodiamond layer can effectively prevent short circuits caused by unavoidable lithium *** Li||Li symmetrical cells assembled with nanodiamond layer modified PP demonstrated a stable cycle of over 1000 h at 2 mA cm-2with a polarization voltage of only 29.3 ***,the negative charged layer serves as a physical barrier blocking lithium polysulfide ions,effectively mitigating capacity *** improved cells achieved a capacity decay of only 0.042%per cycle after 700 cycles at 3 C,demonstrating effective suppression of dendrite growth and capacity attenuation,showing promising prospect.

关键词： Lithium-sulfur batteries Staged dendrite suppression Shuttle effect Surface-negatively-charged nanodiamond

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TR PIV Experimental Investigation on Bypass Transition Induced by a Cylinder Wake

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Chinese Physics Letters 2011年第5期28卷 172-175页

作者： tang zhan-qi JIANG Nan Department of Mechanics Tianjin UniversityTianjin 300072 Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin UniversityTianjin 300372

The process of laminar to turbulent transition induced by a cylinder wake is studied by time-resolved(TR)particle image velocimetry(PIV)in a water *** combination of multi-scale local-averaged structure function analysis with criteria is used to identify the generation of secondary transverse vortex structure andto track its evolution along the *** the beginning of transition,with the decent of cylinder wake vortex,the secondary vortex structure is induced near the *** the secondary vortex moves dovnstream,it is induced to lift up by the wake vortex,meanwhile they are diffused and *** to the method of spatial conditional average,a low-speedhump is found in the near-wallregion along the bypass transition zone,accompanied by a low-speed region in the free stream occupied by the vake *** further downstream,the hump in the near-wall region becomes more and more *** the later stage of transition zone,hairpin vortex can be seen by conditional-averaged low-pass filtered *** hairpin head is almost vertical to the wall with an inclination angle of about 90°,which is attributed to the additional lift-up behavior induced by wake *** can be concluded that in the process of bypass transition,the wake vortex would not only induce the secondary vortex but also leaven its growth and evolution,resulting in the robust and rapidly growing hairpin vortex.

关键词： vortex cylinder averaged

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