Volume 1: Fluid Mechanics最新文献_第7页

The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement 柔性带钢高度对强化对流换热的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5229

Yang Yang, D. Ting, S. Ray

{"title":"The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement","authors":"Yang Yang, D. Ting, S. Ray","doi":"10.1115/ajkfluids2019-5229","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5229","url":null,"abstract":"\u0000 A 12.7 mm wide flexible rectangular strip, made from 0.1 mm-thick aluminum sheet, is experimentally explored as a vortical flow generator for promoting heat convection from a flat plate in a wind tunnel. The strip is positioned normal to the freestream with an incoming velocity of 10 m/s, resulting in a Reynolds number, based on the strip width, of 8,500. The influence of the height of the flexible strip on the convective heat transfer enhancement is of interest. Three strip heights, 25.4 mm, 38.1 mm and 50.8 mm, were investigated. The heat transfer results are expressed in terms of Nusselt number, Nu, normalized by the unperturbed reference Nu0. The shortest, 25.4 mm high flexible strip resulted in the highest peak and overall heat transfer enhancement. The distribution of the local heat transfer enhancement is found to correlate well with the turbulent flow motion detailed using a triple-sensor hot-wire anemometer. Pointedly, the heat transfer rate is most elevated when the local flow is moving toward the hot plate, sweeping across a stretch of the surface before moving away from it. These effective convective motions are most effectively generated by the vortices produced by the shortest strip.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125950852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Influence of Surface Irregularities on Hydrodynamic Instabilities in Couette-Taylor Flow 表面不规则性对库埃特-泰勒流流体动力不稳定性的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4625

Lamia Gaied, Emna Berrich, F. Aloui, M. Lippert, L. Keirsbulck, Maxence Bigerelle

{"title":"Influence of Surface Irregularities on Hydrodynamic Instabilities in Couette-Taylor Flow","authors":"Lamia Gaied, Emna Berrich, F. Aloui, M. Lippert, L. Keirsbulck, Maxence Bigerelle","doi":"10.1115/ajkfluids2019-4625","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4625","url":null,"abstract":"\u0000 In this work, we propose an experimental study of roughness effect on hydrodynamic instabilities’ Couette-Taylor flow. During experiments, the inner cylinder rotates at a given angular velocity and the outer cylinder is maintained fix.\u0000 The main objective of the study is to highlight the geometric parameters’ effect on the flow. We mainly focused our attention on the effect of the wall roughness parameter on the appearance instabilities in the studied configuration (delay or advance in its appearance). For this purpose, a qualitative study was performed using Kalliroscope particles to visualize the instabilities. Then, we applied polarography to different types of roughness as a quantitative study. Hence, the possibility to characterize the flow regimes of the first instabilities (TVF, WVF, MWVF, and TN). The experiments have shown that surface irregularities, have an effect on the appearance of the first instabilities, which depend on the size and nature of the roughness. In fact, the surface roughness not only increases the friction on the wall, but it also greatly influences the transport of the mass and momentum in a given flow regime. The flow, therefore, undergoes more friction when the inner cylinder (in rotation) has a rough surface. This friction slows the velocity of the fluid particles; which delays the onset of instability. The movement of the particles will therefore, be dampened by the irregularities at the level of the rough surface. Moreover, the results also proved that as soon as the Couette-Taylor cells are established, the roughness is no longer a particle motion damper, but on the contrary, it promotes the continuation of the disturbance of the flow. The flow becomes then less slowdown in the hollow of the surface irregularities; which leads to less friction. For higher Taylor numbers, the study showed a faster transition from one regime to another.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"323 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132730166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Can Natural Convection on Smooth Vertical Plates in the Laminar Regime Be Improved by Adding Forward Facing Triangular Roughness Elements? 层流状态下平滑垂直板上的自然对流是否可以通过添加面向前方的三角形粗糙度单元来改善?

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5441

J. Hærvig, A. Jensen, H. Sørensen

{"title":"Can Natural Convection on Smooth Vertical Plates in the Laminar Regime Be Improved by Adding Forward Facing Triangular Roughness Elements?","authors":"J. Hærvig, A. Jensen, H. Sørensen","doi":"10.1115/ajkfluids2019-5441","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5441","url":null,"abstract":"\u0000 Vertical smooth surfaces are commonly used for transferring heat by natural convection. Many studies have tried altering smooth surfaces in various ways to increase heat transfer. Many of these studies fail to increase global heat transfer. The problem commonly reported is dead zones appearing just upstream and downstream obstructions that effectively decrease wall temperature gradients normal to the surface. In this study, we simulate how changes geometry of forward facing triangular roughness elements affect local and global heat transfer for isothermal plates.\u0000 We change the aspect ratio of the triangular elements from L/h = 5 to L/h = 40 at Grashof numbers of GrL = 8.0 · 104 and GrL = 6.4 · 105. In all cases the flow remains laminar. Even when accounting for the increase in surface area, we keep observing a decrease in global heat transfer compared to the smooth vertical plate. However, the results show by carefully selecting the aspect ratio and pitch distance of the triangular elements based on the Grashof number, the dead zone behind the horizontal part can be eliminated thereby significantly increasing local heat transfer. This observation could help to improve cooling of electronics with high localised heat fluxes.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114069894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Contribution of Fluctuating Large-Scale Motions in Turbulent Fluid Flow Through a Channel 波动大尺度运动对紊流流经通道的贡献

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5242

Y. Mito

引用次数: 0

Impact of Differing Water Contents on Electrostatic Charging 不同含水量对静电充电的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4960

Philipp Weishaar, Tobias Mielke, K. Schmitz

引用次数: 0

Experimental Evaluation of Wind Tunnel Test Apparatus for Active Flow Control 主动气流控制风洞试验装置的实验评价

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5462

A. Pesch, D. Hess

{"title":"Experimental Evaluation of Wind Tunnel Test Apparatus for Active Flow Control","authors":"A. Pesch, D. Hess","doi":"10.1115/ajkfluids2019-5462","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5462","url":null,"abstract":"\u0000 Active control of flow dynamics is an ever-increasing field of study. This paper presents details on a new experimental apparatus for the testing of dynamic fluid-structure interaction and the control thereof. Specifically, the experimental apparatus involves an open return wind tunnel with an actuated rigid airfoil. The airfoil is replaceable, but this initial evaluation uses a flat plate as a basic geometry airfoil. The pitch of the airfoil is actively controlled in real-time via an angle sensor, microcontroller, and brushed DC electric motor. For a given PID controller, sine sweeps are performed to identify the closed-loop frequency response at varying wind speeds. The wind creates a destabilizing feedback torque on the airfoil which increases with wind speed and results in a change in the closed-loop frequency response. A model of the system is augmented with a mathematical model for the wind dynamics. The assumed form wind model is manually tuned to match the closed-loop frequency response for all wind speeds. Finally, steady-state tests are conducted in which the setpoint for angle of attack is incrementally changed and the frequency spectrum is found for the angle sensor, in the control loop, and a hotwire behind the airfoil which is not in the control loop. The results from the angle sensor show the system holds steady, with slight variation at low frequencies for high angles of attack. The results from the hotwire show a distinct sheading frequency at low angles of attack, which is replaced by chaotic low frequency flow at high angles of attack characteristic of flow separation.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130004825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Wing-Wake Interaction of Insect-Like Flapping Wing in Hover: Effect of Aspect Ratio and Kinematics at Re~104 悬停时类昆虫扑翼翼-尾迹相互作用:展弦比和Re~104时运动学的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4804

Reynolds Addo-Akoto, Jong-Seob Han, Jae-Hung Han

引用次数: 0

Experimental Study on Suppression of Vortex Shedding Behind a Square Cylinder Using Opposed-Type Plasma Actuators 对置式等离子体作动器抑制方形圆柱后涡脱落的实验研究

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5065

A. Nakazawa, Takuto Yonemichi, K. Fukagata

{"title":"Experimental Study on Suppression of Vortex Shedding Behind a Square Cylinder Using Opposed-Type Plasma Actuators","authors":"A. Nakazawa, Takuto Yonemichi, K. Fukagata","doi":"10.1115/ajkfluids2019-5065","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5065","url":null,"abstract":"\u0000 Vortex shedding in the flow field causes many kinds of problems such as increase of drag and noise. Especially, the von Kármán vortex street behind bluff bodies, e.g. a tire of an airplane and a pantograph of a train, greatly contributes to them. One of the effective methods to suppress the vortices is the use of plasma actuators (PAs). A PA can induce flow by applying a high-voltage and high-frequency AC voltage to its electrodes. In the present study, we use an opposed-type PA (O-PA), which consists of two PAs facing each other. The O-PA can induce a jet in the direction perpendicular to the surface because of a collision of flows induced by the two PAs. In this study, we investigate the control effect of an O-PA on the flow around a square cylinder using an O-PA by means of the PIV measurement. First, we measure the flow induced by an O-PA. It is confirmed that the velocity of the induced flow increases as the applied voltage Vpp increases, and the O-PA induces the jet of about 1.5 m/s under Vpp = 10kV. Next, we measure the flow around a square cylinder with no control. It is confirmed that the von Kármán vortex street occurs behind a square cylinder. Finally, we measure the flow around a square cylinder under the control by the O-PA attached on the rear surface. It is confirmed that the vortex shedding behind a square cylinder is suppressed by the O-PA under Vpp = 10kV.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130378318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Optimizing a Segmented Transmission Line Model for Dynamic Flows in Arbitrarily Tapered Pipelines 任意锥形管道中动态流动分段传输线模型的优化

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4773

T. Wiens

引用次数: 0

Experimental Study of Thermal Performance and Flow Behaviour With Winglets Vortex Generators in a Circular Tube 圆管内小翼涡发生器热性能与流动特性的实验研究

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4723

A. Nurizki, M. Islam, M. Alam

{"title":"Experimental Study of Thermal Performance and Flow Behaviour With Winglets Vortex Generators in a Circular Tube","authors":"A. Nurizki, M. Islam, M. Alam","doi":"10.1115/ajkfluids2019-4723","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4723","url":null,"abstract":"\u0000 Vortex generator (VG) is one of the passive techniques which could improve the heat transfer with relatively low pressure drop. Vortex generators create streamwise longitudinal vortices which does not decay until far downstream that leads to have higher heat transfer with a lower pressure drop. The objectives of this experiment were to study the heat transfer and flow characteristics of fully developed turbulent flow due to different arrangement of VGs in a tube. The experiments were performed by using delta winglet vortex generators in a 52 mm circular copper tube. The flow regime varied from 6000 to 27000 Reynolds number. Four vortex generators with 45° angle of attack were used inside the circular tube. Different parameters of the VGs studied in this experiment such as lengths (L = 10, 15, and 20 mm) and arrangements (R = 0° to −15°). The results indicate that the length affected friction factor (f) and Nusselt number (Nu) significantly. L20 reached the highest f and Nu. The staggered arrangement concludes a significant drop on friction factor and a significant increase on Nusselt number. Consequently, the thermal performance of all staggered arrangement cases could reach a significant rise compared to the inline arrangement. The oil flow visualization could track down the trace of vortex behind the VG. The inline arrangement showed a strong vortex formed as a result of VG which was related to higher f while the staggered arrangement indicated a weak vortex.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115264070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1