Volume 1: Fluid Mechanics最新文献_第9页

Phototactic Behaviour of Active Fluids: Effects of Light Perturbation on Diffusion Coefficient of Bacterial Suspensions 活性流体的光致行为:光扰动对细菌悬浮液扩散系数的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4904

T. Vourc’h, J. Léopoldès, H. Peerhossaini

{"title":"Phototactic Behaviour of Active Fluids: Effects of Light Perturbation on Diffusion Coefficient of Bacterial Suspensions","authors":"T. Vourc’h, J. Léopoldès, H. Peerhossaini","doi":"10.1115/ajkfluids2019-4904","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4904","url":null,"abstract":"\u0000 Active fluids refer to the fluids that contain self-propelled particles such as bacteria or micro-algae, whose properties differ fundamentally from the passive fluids. Such particles often exhibit an intermittent motion; with high-motility “run” periods separated by low-motility “tumble” periods. The average motion can be modified with external stresses, such as nutrient or light gradient, leading to a directed movement called chemotaxis and phototaxis, respectively.\u0000 Using cyanobacterium Synechocystis sp.PCC 6803, a model micro-organism to study photosynthesis, we track the bacterial response to light stimuli, under isotropic and non-isotropic conditions. In particular, we investigate how the intermittent motility is influenced by illumination.\u0000 We find that just after a rise in light intensity, the probability to be in the run state increases. This feature vanishes after a typical time of about 1 hour, when initial probability is recovered. Our results are well described by a model based on the linear response theory.\u0000 When the perturbation is anisotropic, the characteristic time of runs is longer whatever the direction, similar to what is observed with isotropic conditions. Yet we observe a collective motion toward the light source (phototaxis) and show that the bias emerges because of more frequent runs towards the light.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"63 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":"124548935","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

Delta Winglet Pairs in the Core of a Pipe and its Effect on Heat Transfer and Flow 管道核心的δ小波对及其对传热和流动的影响

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5382

M. D. Islam, Z. Chong, M. Alam

{"title":"Delta Winglet Pairs in the Core of a Pipe and its Effect on Heat Transfer and Flow","authors":"M. D. Islam, Z. Chong, M. Alam","doi":"10.1115/ajkfluids2019-5382","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5382","url":null,"abstract":"\u0000 Vortex generators/turbulent promoters generate the longitudinal vortices which introduce the better mixing of the fluid with fluid circulation and enhance heat transfer. In this research, experimental investigations have been carried out to study the effect of delta winglet vortex generator (DWVG) in the core of the pipe on heat transfer and flow behavior. In this experiment, two pairs of delta winglet vortex generators (DWVG) were printed on the upside and downside of the thin plate using 3D printing technology in a ring and then placed in the core of the pipe to generate longitudinal vortices. Middle plate was very thin. The effect of heights (H = 5mm, 10mm, 15mm and 20mm) of DWVG for 10° angle of attack and 15mm spacing between leading edges of VG pairs on heat transfer and pressure drop was studied. The experiments were conducted for a fully developed turbulent flow of air in the range of Reynolds numbers (Re) 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number (Nu) and friction factor (f). The experimental results indicate that DWVG in the core of the tube results in a considerable increase in Nu with some pressure penalty. It is found that DWVG increase Nu considerably only when H is over 10mm. Nu increases with Re and H. Friction factor decreases with Re but increase with H. The thermal performance enhancement (TPE) was noticed decreasing with Re. TPE could be obtain up to 1 only when the height is over 10mm for Re ≤ 7500. The experimental results show that the DWVG in the core of the pipe is not a good option to enhance the heat transfer at a higher Re.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"30 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":"122590819","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

Ionic Wind Application to Vortex Ring Generator and its Transportation Efficiency 离子风在涡环发生器中的应用及其输送效率

Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5141

Fukunaga Kengo, Satake Masayoshi, N. Maeda, Kazushi Shikata, Tomohisa Ezaka

引用次数: 0

Decay of Turbulence in a Duct With Transverse Magnetic Field 横磁场作用下管道湍流的衰减

Volume 1: Fluid Mechanics Pub Date : 2018-09-27 DOI: 10.1115/ajkfluids2019-4688

O. Zikanov, D. Krasnov, T. Boeck, S. Sukoriansky

引用次数: 0

Resolvent Analysis of Turbulent Friction Drag Reduction by Manipulation of Mean Velocity Profile 操纵平均速度剖面的湍流摩擦减阻的解析分析

Volume 1: Fluid Mechanics Pub Date : 1900-01-01 DOI: 10.1115/ajkfluids2019-5125

Riko Uekusa, Aika Kawagoe, Yusuke Nabae, K. Fukagata

{"title":"Resolvent Analysis of Turbulent Friction Drag Reduction by Manipulation of Mean Velocity Profile","authors":"Riko Uekusa, Aika Kawagoe, Yusuke Nabae, K. Fukagata","doi":"10.1115/ajkfluids2019-5125","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5125","url":null,"abstract":"\u0000 In the present study, we numerically manipulate the mean velocity profile of a turbulent channel flow and assess the friction drag reduction performance by using resolvent analysis. Building on the implication obtained from Kühnen et al. (Nat. Phys., Vol. 14, 2017, pp. 386–390) that modifying mean velocity profile flat leads to significant drag reduction, we first introduce two functions for turbulent mean velocity, which can express ‘flattened’ profiles: one is derived based on the turbulent viscosity model proposed by Reynolds & Tiederman (J. Fluid Mech., Vol. 658, 2010, pp. 336–382), and the other is based on the mean velocity profile of laminar flow. These functions are used as the mean velocity profile for the resolvent analysis, and the flatness of the resulting profiles is characterized by two different measures. As a result, we confirm that, friction drag reduction is achieved if the turbulent mean velocity profile is ‘flattened’. However, we also find that the flatness of the mean velocity profile in the center of the channel alone is not enough to evaluate the drag reduction performance.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122066746","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