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Volume 1: Fluid Mechanics最新文献

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The Reynolds Stress in Channel Flows From a Lagrangian Treatment of the Turbulence Momentum 从湍流动量的拉格朗日处理看沟道流动中的雷诺应力
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5031
T.-W. Lee
{"title":"The Reynolds Stress in Channel Flows From a Lagrangian Treatment of the Turbulence Momentum","authors":"T.-W. Lee","doi":"10.1115/ajkfluids2019-5031","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5031","url":null,"abstract":"\u0000 We have developed a mechanistic approach for determination of the Reynolds stress, using a Lagrangian analysis of turbulent momentum. Analysis and comparison with DNS and experimental data point toward the soundness of this approach (Lee, 2018). von Karman constant, the inner layer thickness and the Reynolds stress itself are all recovered through this approach, in agreement with DNS data. In addition, the turbulent flow profiles can be calculated iteratively using the basic Reynolds-averaged Navier-Stokes equation, in conjunction with the current transport equation for the Reynolds stress. In this work, we explore these and further uses of the current approach in solving turbulent flow dynamics.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"13 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":"115397428","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
Directional Surface Roughness Influence on Turbulent Flow Structure 定向表面粗糙度对湍流结构的影响
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5615
Z. Harun, A. Abbas, B. Nugroho
{"title":"Directional Surface Roughness Influence on Turbulent Flow Structure","authors":"Z. Harun, A. Abbas, B. Nugroho","doi":"10.1115/ajkfluids2019-5615","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5615","url":null,"abstract":"\u0000 A series of experiments have been conducted to investigate turbulent flow structures when it is exposed to a highly directional riblet-type surfaces roughness (converging-diverging/herringbone pattern) at a relatively low Reynolds number (Reτ). These experiments show that even at a low Reτ, the surface pattern is able to modify the turbulent boundary layer. Over the diverging region, we observe a decrease in drag penalty, while over the converging region there is an increase of drag penalty, which is indicated by the shift in the mean velocity profiles. The surface roughness also influences the turbulence production, indicated by the elevated turbulence intensities profiles for both the converging and diverging regions. The result seems to deviate from early investigations that show an increase in turbulence intensities above the converging region and a lowered turbulence intensities above the diverging region. The discrepancy may be caused by the lower Reτ Ret in the current report. Other important statistics such as skewness and flatness are also reported.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"178 6 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":"126134636","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: 2
Multiple Shock Waves and its Unsteady Characteristics in Internal Flows 内部流动中的多重激波及其非定常特性
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5087
J. K. James, H. Kim
{"title":"Multiple Shock Waves and its Unsteady Characteristics in Internal Flows","authors":"J. K. James, H. Kim","doi":"10.1115/ajkfluids2019-5087","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5087","url":null,"abstract":"\u0000 Shock wave turbulent boundary layer interaction is a fundamental phenomenon observed in most of the gas dynamics applications such as wind tunnels, supersonic air intakes, transonic airfoil, nozzle flows, etc. The flow field and shock wave pattern in a constant area duct are analyzed experimentally. The focus of the present study is to present the time-resolved flow characteristics of the multiple shock waves and its oscillations. High-speed Schlieren flow visualization is used to capture the transient shock structure in the wind tunnel constant area test section. A gradient-based image processing was incorporated to capture the shock excursion details. Results indicate that the shock pattern is unsymmetrical in the flow field. The foot of the lambda shock wave in the upper and lower exhibit a difference in axial location and there is a large difference in this value at the mean position when the shock moves in the upstream direction compared to the downstream movement.","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":"125922296","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: 2
Characterization of Thermals in a Heated Turbulent Boundary Layer 热湍流边界层中热流体的表征
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-5436
K. Dennis, K. Siddiqui
{"title":"Characterization of Thermals in a Heated Turbulent Boundary Layer","authors":"K. Dennis, K. Siddiqui","doi":"10.1115/ajkfluids2019-5436","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5436","url":null,"abstract":"The hydrodynamic boundary layer encountered in many practical engineering systems is turbulent in nature and known to play a significant role in governing the induced friction drag and species transport. In turbulent boundary layer flows, heat transfer is often involved which increases flow complexity due to the influence of buoyancy. When the buoyant force is sufficiently large in magnitude, thermals carrying heated fluid are known to detach and rise from the wall. Literature review shows that in mixed convection, thermals have been primarily identified through qualitative flow visualizations and there is a scarcity of their quantitative assessment. Furthermore, the evolution of thermals in the boundary layer with respect to flow inertia and viscous shear is not well-understood. Hence, there is a need for a better understanding of the dynamics of thermals in mixed convection turbulent boundary layer flow. The objective of this study is to experimentally investigate the three-dimensional nature of thermals rising from a turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop low-disturbance wind tunnel with a test section featuring a 1 m long heated bottom wall. The multi-plane particle image velocimetry (PIV) technique was used to capture images in multiple planes with respect to the turbulent boundary layer mean flow direction for three-dimensional characterization. The measurements were conducted at Richardson numbers (Ri) of 0.3, 1.0, and 2.0. Flow visualization images are used to describe the nature of thermals and the dynamical processes involved during their interaction with bulk boundary layer flow. An image processing algorithm to detect thermals is then detailed and applied to experimental images. The performance of the new algorithm is then assessed in its ability to detect thermals.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"76 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":"127528980","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
Effect of the Large-Scale Structure on Turbulent Prandtl Number in a Turbulent Shear Layer 湍流剪切层中大尺度结构对湍流普朗特数的影响
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4722
K. Takamure, Y. Sakai, Yasumasa Ito, K. Iwano
{"title":"Effect of the Large-Scale Structure on Turbulent Prandtl Number in a Turbulent Shear Layer","authors":"K. Takamure, Y. Sakai, Yasumasa Ito, K. Iwano","doi":"10.1115/ajkfluids2019-4722","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4722","url":null,"abstract":"\u0000 We have run a Direct Numerical Simulation of a spatially developing shear mixing layer. The aim of this study is to clarify the influence of the large-scale structure on the turbulent Prandtl number PrT. As a main conclusion, PrT takes a small value (PrT ∼ 0.5) in the dominant region of the large-scale structure. The budget analyses for the Reynolds stress equation and the scalar flux equation revealed that the differences between the momentum and scalar transfer are caused by terms related to pressure (i.e., pressure-strain correlation term, pressure-scalar gradient correlation term, and pressure diffusion terms). Phenomenally, the momentum in the field where a large-scale vortex coexists tends to be transported toward the counter-gradient direction under the influence of pressure, but the scalar is transported toward the gradient direction. As a result, it is thought that the difference in the driving force between the momentum and scalar transport causes the decrease of the PrT.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"50 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":"121866098","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
Effects of Rectangular Column Flanges in Steel Structures on Motion-Induced Vortex Vibration 钢结构矩形柱法兰对运动诱导涡振动的影响
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4620
K. Matsuda, Kusuo Kato, Kazufumi Ejiri, N. Cao
{"title":"Effects of Rectangular Column Flanges in Steel Structures on Motion-Induced Vortex Vibration","authors":"K. Matsuda, Kusuo Kato, Kazufumi Ejiri, N. Cao","doi":"10.1115/ajkfluids2019-4620","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4620","url":null,"abstract":"\u0000 A spring-supported test for a rectangular cross section with the side ratio of B/D = 1.18 (B: along-wind length, D: cross-wind length) was conducted to simulate the phenomenon in a closed circuit wind tunnel at Kyushu Institute of Technology. A new finding was that vibrations were confirmed in the neighborhoods of reduced wind speeds Vr = V/fD = 2 and Vr = 8 (V: wind speed (m/s), f: natural frequency (Hz)). Because the reduced wind speed in motion-induced vortex vibration is calculated as Vr = 1.67 × B/D = 1.67 × 1.18 = 2.0, vibrations around Vr = 2 were considered to be motion-induced vortex vibration. On the other hand, vibrations around Vr = 8 were considered to be Kármán vortex-induced vibrations, because Vr = 1/St = 8.1. St has a Strouhal number of 0.124 measured by wind tunnel test using a rectangular cross section of B/D = 1.18.\u0000 In this paper, the authors focused on the wind tunnel model configuration. Rectangular column flanges in steel structures have not usually been taken into account when manufacturing wind tunnel test models. Wind tunnel tests were carried out in order to clarify the effects of rectangular column flanges in steel structures on motion-induced vortex vibration. Spring-supported tests, smoke flow visualizations and measurements of Strouhal number and unsteady aerodynamic lift were performed with or without flanges changing angle of attack. Models were forced-oscillating in smoke flow visualizations and unsteady aerodynamic lift measurements. All wind tunnel tests were conducted in a smooth flow. As a result, it was found that it could be very important to model rectangular column flanges in steel structures for wind tunnel tests, especially bracing members of long-spanned truss bridges from a wind engineering point of view.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"54 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":"116727745","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
Unsteady Vortex Breakdown Phenomena in an Enclosed Cylindrical Container With a Rotating Endwall Disk 具有旋转端壁盘的封闭圆柱形容器内的非定常涡击穿现象
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4751
Yuki Nakatsuka, R. Iwatsu, J. Hyun, H. Koyama
{"title":"Unsteady Vortex Breakdown Phenomena in an Enclosed Cylindrical Container With a Rotating Endwall Disk","authors":"Yuki Nakatsuka, R. Iwatsu, J. Hyun, H. Koyama","doi":"10.1115/ajkfluids2019-4751","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4751","url":null,"abstract":"\u0000 A high-quality precision-controlled turntable apparatus was fabricated to probe the dynamic behavior of a viscous fluid contained in a cylindrical container. Vortex breakdown(s) produced by a rotating endwall disk was visualized by using a fluorescent dye injection technique, and its flow field was measured by using a particle image velocimetry. This flow is characterized by two non-dimensional parameters, i.e., the height-to-radius ratio H/R and the rotating Reynolds number Re = Ω2/v. Limiting boundaries for single, double and triple vortex breakdowns in steady flow were re-plotted to compare with the previous visualization studies of Escudier. The locations of stagnation points of the vortex breakdown bubble(s) in steady flow were measured quantitatively. The overall experimental results in the steady flow were in excellent agreement with Escudier’s data. In unsteady flow, the amplitude and time period of periodic axial oscillation, and the polar angle and time period of precession, were measured. The domains for periodic axial oscillation and for precession in unsteady flow were delineated.","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":"114590869","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
Using Jet Engine Simulator in Propulsion Education 喷气发动机模拟器在推进教学中的应用
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4963
R. Taghavi, S. Farokhi
{"title":"Using Jet Engine Simulator in Propulsion Education","authors":"R. Taghavi, S. Farokhi","doi":"10.1115/ajkfluids2019-4963","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4963","url":null,"abstract":"\u0000 Undergraduate education in jet propulsion can benefit from a modern real-engine simulator. The traditional lecture/laboratory course in propulsion continues to emphasize fundamental aerothermodynamics and often includes a propulsion laboratory that tests small engines (e.g., micro-turbojet engines) mounted on a thrust stand. Modern engine simulators, as virtual test bench, offer new tools and capabilities that help students learn the fundamentals as well as jet engine response to dynamic throttle setting. Geared, high-bypass ratio, two-spool turbofan engines can be simulated in a virtual test bench from takeoff to cruise at different altitudes and Mach numbers. The simulator employs an electric start, a real FADEC (Full Authority Digital Electronic Control) system and system communication that is coupled to a real power lever. The tools that are embedded in the virtual test bench allows for various studies, including control systems, comparing open-loop and closed-loop control. The integration of a state-of-the-art engine simulator in the jet propulsion course at the University of Kansas, Aerospace Engineering shows enhanced student engagement and learning.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"67 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":"114835000","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
The Performance Enhancement of Hemodialyzers: Computational Fluid Dynamics Study 血液透析器性能增强:计算流体动力学研究
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4863
Abdullah A. Alghafis, Ahmed M. Alshwairekh, Anas M. Alwatban, U. Alqsair, A. Oztekin
{"title":"The Performance Enhancement of Hemodialyzers: Computational Fluid Dynamics Study","authors":"Abdullah A. Alghafis, Ahmed M. Alshwairekh, Anas M. Alwatban, U. Alqsair, A. Oztekin","doi":"10.1115/ajkfluids2019-4863","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4863","url":null,"abstract":"\u0000 Computational fluid dynamics simulations are conducted to study the hemodialysis process in separation modules containing hollow fiber membranes. Hemodialysis is the filtration process which removes waste out of the blood. In this work, three-dimensional steady-state laminar flow simulations are conducted to investigate the effect of disk baffles on the performance of the hemodialysis process. The uniformly spaced baffles are placed along the axis of the shell within the dialyzer. The disk baffles of diameter 2.85 dhd were considered, where dhd is the shell hydraulic diameter. The inlet solute mass fraction of the blood solution is fixed at 0.00074, while the inlet solute mass fraction of the dialysate solution varied as 0.004 and 0.007. The blood and the dialysate flow rates are fixed. Our results revealed that the presence of disk baffles in the shell mitigates the concentration polarization and yields higher urea permeation. The higher dialysate concentration solute yields a 41.2% increase in the urea permeate rate compared to the lower dialysate solute concentration.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"41 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":"126031568","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
Experimental Characterization of a Micro-Blower for Flow Control 用于流量控制的微型鼓风机的实验特性
Volume 1: Fluid Mechanics Pub Date : 2019-07-28 DOI: 10.1115/ajkfluids2019-4772
Maria Wu, P. Sullivan
{"title":"Experimental Characterization of a Micro-Blower for Flow Control","authors":"Maria Wu, P. Sullivan","doi":"10.1115/ajkfluids2019-4772","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4772","url":null,"abstract":"\u0000 A compact, lightweight, low-power piezoelectric micro-blower was characterized using particle image velocimetry to determine its flow control potential. The micro-blower has been operated in continuous mode as well as in burst mode using two different actuation frequencies. The maximum mean velocity measured with the micro-blower operating in continuous mode was approximately Ūmax = 13 m/s which occurred at the centerline at an approximate stream-wise location of x/d = 4. The velocity profiles in the developed region resemble those of turbulent jets. The momentum-flux from the micro-blower in continuous mode was significantly greater than a typical synthetic jet actuator which was successfully used for flow control, indicating that the micro-blower can impart the necessary momentum to be effective for flow control. With burst mode, the results show that the micro-blower could impart an even greater momentum.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"116 12","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113999841","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
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