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基于遗传算法的带有调纵倾尾板及拦截器的滑行艇水动力性能评估及优化 预览
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作者 Abdollah Sakaki Hassan Ghassemi Shayan Keyvani 《船舶与海洋工程学报:英文版》 CSCD 2019年第2期131-141,共11页
Nowadays,several stern devices are attracting a great deal of attention.The control surface is an effective apparatus for improving the hydrodynamic performance of planing hulls and is considered an important element ... Nowadays,several stern devices are attracting a great deal of attention.The control surface is an effective apparatus for improving the hydrodynamic performance of planing hulls and is considered an important element in the design of planing hulls.Control surfaces produce forces and a pitching moment due to the pressure distribution that they cause,which can be used to change the running state of high-speed marine boats.This work elaborates a new study to evaluate the hydrodynamic performance of a planing boat with a trim tab and an interceptor,and optimizes them by using an optimization algorithm.The trim tab and the interceptor have been used to optimize the running trim and motion control of semi-planing and planing boats at various speeds and sea conditions for many years.In this paper,the usage of trim tab is mathematically verified and experimental equations are utilized to optimize the performance of a planing boat at a specificd trim angle by using an optimization algorithm.The genetic algorithm(GA)is one of the most useful optimizing methods and is used in this study.The planing boat equations were programmed according to Savitsky’s equations and then analyzed in the framework of the GA-based optimization for performance improvement of theplaning hull.The optimal design of trim tab and interceptor for planing boat can be considered a multiobjective problem.The input data of GA include different parameters,such as speed,longitudinal center of gravity,and deadrise angle.We can extract the best range of forecasting the planing boat longitudinal center of gravity,the angle of the trim,and the least drag force at the best trim angle of the boat. 展开更多
关键词 Trimtab INTERCEPTOR Drag force Genetic ALGORITHM Optimization ALGORITHM
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Hybrid Isothermal Model for the Ferrohydrodynamic Chemically Reactive Species
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作者 Noor Muhammad S.Nadeem M.T.Mustafa 《理论物理通讯:英文版》 SCIE CAS CSCD 2019年第4期384-392,共9页
A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer flow is established.The characteristics of Newtonian heating and magnetic dipole in a ferrofluid due to a stret... A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer flow is established.The characteristics of Newtonian heating and magnetic dipole in a ferrofluid due to a stretchable surface is analyzed for three chemical species.It is presumed that the isothermal cubic autocatalator kinetic gives the homogeneous reaction and the first order kinetics gives the heterogeneous(surface)reaction.The analysis is carried out for equal diffusion coefficients of all autocatalyst and reactions.Heat flux is examined by incorporating Fourier’s law of heat conduction.Characteristics of materialized parameters on the magneto-thermomechanical coupling in the flow of a chemically reactive species are investigated.Further,the heat transfer rate and friction drag are depicted for the ferrohydrodynamic chemically reactive species.It is evident that the Schmidt number has increasing behavior on the rate of heat transfer in the boundary layer.Comparison with available results for specific cases is found an excellent agreement. 展开更多
关键词 FERROMAGNETIC fluid HYBRID chemically REACTIVE species NEWTONIAN HEATING heat transfer FRICTION drag
超燃冲压发动机推力性能评估方法
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作者 吴颖川 贺元元 +3 位作者 张小庆 任虎 刘伟雄 乐嘉陵 《推进技术》 EI CAS CSCD 北大核心 2019年第1期26-32,共7页
超燃冲压发动机与飞行器紧密耦合,使得在地面试验直接测量发动机流道有效推力非常困难。为了更有效获得发动机推力性能,提出了一种基于机体推进一体化性能试验的评估方法,基于脉冲燃烧风洞带动力一体化测力试验直接获得飞行器的整机净... 超燃冲压发动机与飞行器紧密耦合,使得在地面试验直接测量发动机流道有效推力非常困难。为了更有效获得发动机推力性能,提出了一种基于机体推进一体化性能试验的评估方法,基于脉冲燃烧风洞带动力一体化测力试验直接获得飞行器的整机净推力。基于净推力加机体外阻的方法获得了发动机有效推力。同时提出了一种通过流量计测量飞行器机体外阻的试验技术,并对测量误差进行了分析(均方根误差小于2.54%)。与传统的台架推力差减内阻的方法相比,该方法把发动机流道内阻计算转为飞行器机体外阻计算或测量,为超燃冲压发动机推力性能评估提供了一种全新思路。 展开更多
关键词 超燃冲压发动机 机体推进一体化 脉冲燃烧风洞 推力 阻力 比冲
Delayed Detached Eddy Simulation of Subcritical Flow past Generic Side Mirror
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作者 陈鑫 李铭 《上海交通大学学报:英文版》 EI 2019年第1期107-112,共6页
In the present study, the subcritical flow past a generic side mirror on a base plane is investigated at the Reynolds number of 5.2 × 10~5 using delayed detached eddy simulation(DDES) turbulence model. Asides fro... In the present study, the subcritical flow past a generic side mirror on a base plane is investigated at the Reynolds number of 5.2 × 10~5 using delayed detached eddy simulation(DDES) turbulence model. Asides from the capability of capturing main features of the large recirculation vortex in the wake of the side mirror and the front horseshoe vortex, the accuracy of DDES estimation of recirculation length is significantly increased by over20%, compared to the detached eddy simulation(DES) estimation using the same grid. And DDES prediction of pressure coefficient at the trailing edge of the mirror is in good agreement with the experiments, which is more accurate than both DES and large eddy simulation(LES) results. The results verify the capacity of DDES turbulence model to solve the turbulent flow around the side mirror. This is a key foundation for possible future study of full simulation of external flow field of vehicle. 展开更多
关键词 DELAYED DETACHED EDDY simulation drag recirculation length GENERIC SIDE MIRROR
紫藤萝复叶气动特性的风洞实验研究 预览
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作者 俞科杰 邵传平 《力学学报》 EI CSCD 北大核心 2019年第1期245-262,共18页
树叶的形状重构和减阻能力在太阳能帆板、机翼结构、仿生天线设计和新型发电技术等方面具有应用价值.紫藤萝羽状复叶垂直悬挂于风洞中,在风速0~25 m/s范围内进行正面和反面迎风测试.发现存在前期稳定、中间过渡和后期稳定3个阶段以及5... 树叶的形状重构和减阻能力在太阳能帆板、机翼结构、仿生天线设计和新型发电技术等方面具有应用价值.紫藤萝羽状复叶垂直悬挂于风洞中,在风速0~25 m/s范围内进行正面和反面迎风测试.发现存在前期稳定、中间过渡和后期稳定3个阶段以及5个临界风速.在前期阶段叶轴随风速弯曲变化剧烈,出现小叶分层飞翼和分层多形状稳定.过渡阶段出现叶轴大幅低频振动和部分小叶小幅高频振动两种不稳定形式.后期出现两层或单一整体稳定,横截面形状分为锥形、楔形和U形.随着风速增大,复叶宽度减小,小叶层数逐步减少,直至出现流线形单一整体.随着雷诺数增大,复叶阻力系数先是快速下降,后又缓慢地趋于常数.复叶Vogel负指数绝对值|α|随小叶数目的增大而增大.反面迎风时|α|比正面迎风时大,但随着小叶数目增加两者趋于一致.当复叶旋涡脱落频率与叶轴固有频率接近时,叶轴出现大幅振动.理论分析得到叶轴振动的第二临界风速V2/√E/P是b/l和d/l的函数,其中E,P,d和l分别为叶轴弹性模量、密度、直径和长度,b为变形后的复叶宽度,并由实验数据得到了其变化图. 展开更多
关键词 树叶 形状重构 振动 临界风速 阻力 Vogel指数
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Studies on Factors Influencing Hydrodynamic Characteristics of Plates Used in Artificial Reefs 预览
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作者 TANG Yanli YANG Wenzhao +3 位作者 SUN Liyuan ZHAO Fenfang LONG Xiangyu WANG Gang 《中国海洋大学学报:英文版》 SCIE CAS CSCD 2019年第1期193-202,共10页
As a simplified model of artificial reefs,a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs.T... As a simplified model of artificial reefs,a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs.The models are grouped by various opening numbers and opening-area ratios.They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds.The simulation results are found in good agreement with the experimental measurements.By the non-dimensional analysis,the drag coefficient specified to each model is achieved and the effects of openings are examined.It is found that the key factor affecting the drag coefficient is the open-area ratio.Generally,the drag coefficient is a linear function of the open area ratio with a minus slope.The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data.They will be good references for the design of new artificial reefs.As a result of numerical simulation,the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models. 展开更多
关键词 artificial REEFS drag COEFFICIENT HYDRODYNAMIC characteristics model EXPERIMENT
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Preface:symposium on turbulence structures and aerodynamic heat/force(STSAHF2018)——scientific significance of turbulence research 预览
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作者 Cunbiao LEE ZuoliXIAO Shiyi CHEN 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第2期181-184,共4页
Most fluid flows in nature and engineering applications are in the state of turbulence.Turbulent motions usually exhibit a wide range of spatial and temporal scales,such as the flow of natural gas and oil in pipelines... Most fluid flows in nature and engineering applications are in the state of turbulence.Turbulent motions usually exhibit a wide range of spatial and temporal scales,such as the flow of natural gas and oil in pipelines,the wakes of cars and submarines,the boundary layer of an aircraft,the current in the ocean surface,the atmospheric boundary layer,the interstellar gas clouds(gaseous stars),and the Earth’s wake in the solar wind.Turbulence can greatly improve the heat and mass transfer efficiency of macroscopic flow.For example,chemical engineers use turbulence to mix up and homogenize fluid components and to increase chemical reaction rates in liquids or gases.However,turbulence can also lead to increases in drag,aerodynamic heat,and hydrodynamic and aerodynamic noise.For instance,the aerodynamic loading of high-speed aircraft can be significantly increased due to turbulence. 展开更多
关键词 loading can MOST CARS drag gas MIX be
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Reduction of turbulent boundary layer drag through dielectric-barrier-discharge plasma actuation based on the Spalding formula
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作者 武斌 高超 +3 位作者 刘峰 薛明 王玉帅 郑博睿 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2019年第4期107-114,共8页
It is a very difficult task to develop a method of reducing turbulent boundary layer drag.However,in recent years,plasma flow control technology has demonstrated huge potential in friction drag reduction.To further in... It is a very difficult task to develop a method of reducing turbulent boundary layer drag.However,in recent years,plasma flow control technology has demonstrated huge potential in friction drag reduction.To further investigate this issue,a smooth plate model was designed as a testing object arranged with a bidirectional dielectric-barrier-discharge(DBD)plasma actuator.In addition,measurement of skin friction drag was achieved by applying hot wire anemometry to obtain the velocity distribution of the turbulent boundary layer.A method of quantifying the friction drag effect was adopted based on the Spalding formula fitted with the experiment data.When plasma actuation was conducted,a velocity defect occurred at the two measuring positions,compared with the no plasma control condition;this means that the DBD plasma actuation could reduce the drag successfully in the downstream of the actuator.Moreover,drag reduction caused by backward actuation was slightly more efficient than that caused by forward actuation.With an increasing distance from plasma actuation,the drag-reduction effect could become weaker.Experimental results also show that the improvement of drag-reduction efficiency using a DBD plasma actuator can achieve about 8.78%in the local region of the experimental flat model. 展开更多
关键词 DBD plasma ACTUATOR flow control Spalding FORMULA drag REDUCTION turbulent boundary layer
Mathematical Model of Drag Torque with Surface Tension in Single-Plate Wet Clutch
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作者 Zengxiong Peng Shihua Yuan 《中国机械工程学报:英文版》 SCIE EI CAS CSCD 2019年第2期93-99,共7页
Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes... Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The e ects of surface tension and static contact angles during aeration are nonnegligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with di erent surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two di erent contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier–Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the e ects of surface tension and contact angle. The model shows that the e ects at the beginning of aeration of oil film are significant. These e ects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not a ect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics(CFD) model based on volume of fluid(VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the e ects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration. 展开更多
关键词 Drag TORQUE WET CLUTCH Surface tension Contact ANGLE
Experimental study of drag reduction characteristics related to the multifactor coupling of a bionic jet surface 预览
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作者 Yun-qing Gu Song-wei Yu +3 位作者 Jie-gang Mou Tian-xing Fan Shui-hua Zheng Gang Zhao 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第1期186-194,共9页
To study the drag reduction of a jet surface,an experiment is conducted with a gyrorotor model.The aim of this study is to analyze the influence of the jet aperture,the jet angle and the rotational velocity coupled wi... To study the drag reduction of a jet surface,an experiment is conducted with a gyrorotor model.The aim of this study is to analyze the influence of the jet aperture,the jet angle and the rotational velocity coupled with the jet velocity on the friction torque acting on a jet surface model by using a jet surface drag reduction testing experimental platform.The drag reduction characteristics of the jet surface are also studied.The results show that the maximum drag reduction rate is attained when the jet diameter is 5 mm and the jet velocity is 1.2 m/s.The influence of the jet velocity on the drag reduction rate decreases as the diameter decreases.However,the maximum drag reduction rate can be attained when the angle of the jet is 30° and the velocity of the jet is 1.0 m/s.When the jet diameter is small,the influence of the jet velocity on the drag reduction rate is small,whereas the maximum drag reduction rate is attained when the jet angle is 30° and the jet velocity is 1.0 m/s.When the jet angle is 15°,the drag reduction rate fluctuation is distinct.The maximum drag reduction rate is attained when the rotational velocity is 2 100 r/min and the jet velocity is 1.0 m/s.The results show that the best scheme is A2B2D3 A maximum drag reduction rate of 8.57% can be attained.The effective control of the jet effect on the separation of the boundary layer demonstrates the drag reduction principle of a bionic jet surface. 展开更多
关键词 Drag reduction BIONIC JET SURFACE FRICTION TORQUE COUPLING experiment
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The structure of turbulent flow through submerged flexible vegetation 预览
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作者 Wen-xin Huai Jiao Zhang +3 位作者 Gabriel G.Katul Yong-guang Cheng Xue Tang Wei-jie Wang 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期274-292,共19页
The hydrodynamics of turbulent flow through submerged flexible vegetation is investigated in a flume using acoustic Doppler velocimetery(ADV)measurements.The flow characteristics such as the energetics and momentum tr... The hydrodynamics of turbulent flow through submerged flexible vegetation is investigated in a flume using acoustic Doppler velocimetery(ADV)measurements.The flow characteristics such as the energetics and momentum transfer derived from convcntional spectral and quadrant analyses are considered as the flow encounters a finite vegetation patch.Consistent with numerous canopy flow experiments,a shear layer and coherent vortex structures near the canopy top emerge caused by Kelvin-Helmholtz instabilities after the flow equilibrates with the vegetated layer.These in stabilities are commonly attributed to velocity differences between non-vegetated and vegetated canopy layers in agreement with numerous experiments and simulations conducted on dense rigid canopies.The power-spectral density function for vertical velocity turbulent fluctuations at different downstream positions starting from the edge of the vegetation layer are also computed.For a preset water depth,the dominant dimensionless frequency is found to be surprisingly invariant around 0.027 despite large differences in vegetation densities.The ejection and sweep events significantly contribute to the Reynolds stresses near the top of the vegetation.The momentum flux carried by ejections is larger than its counterpart carried by the sweeps above the canopy top.However,the momentum flux carried by sweeps is larger below the top of the canopy. 展开更多
关键词 Artificial flexible VEGETATION COHERENT VORTEX structures drag force open channel flow VELOCITY distribution
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Effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows 预览
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作者 Yitong FAN Cheng CHENG Weipeng LI 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第3期331-342,共12页
As the Reynolds number increases,the skin friction has been identified as the dominant drag in many practical applications.In the present paper,the effects of the Reynolds number on the mean skin friction decompositio... As the Reynolds number increases,the skin friction has been identified as the dominant drag in many practical applications.In the present paper,the effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows up to Reτ=5 200 are investigated based on two different methods,i.e.,the Fukagata-Iwamoto-Kasagi(FIK)identity(FUKAGATA,K.,IWAMOTO,K.,and KASAGI,N.Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows.Physics of Fluids,14(11),L73–L76(2002))and the Renard-Deck(RD)identity(DECK,S.,RENARD,N.,LARAUFIE,R.,and WEISS,P.′E.Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to Reθ=13 650.Journal of Fluid Mechanics,743,202–248(2014)).The direct numerical simulation(DNS)data provided by Lee and Moser(LEE,M.and MOSER,R.D.Direct numerical simulation of turbulent channel flow up to Reτ≈5 200.Journal of Fluid Mechanics,774,395–415(2015))are used.For these two skin friction decomposition methods,their decomposed constituents are discussed and compared for different Reynolds numbers.The integrands of the decomposed constituents are locally analyzed across the boundary layer to assess the actions associated with the inhomogeneity and multi-scale nature of turbulent motion.The scaling of the decomposed constituents and their integrands are presented.In addition,the boundary layer is divided into three sub-regions to evaluate the contributive proportion of each sub-region with an increase in the Reynolds number. 展开更多
关键词 drag DECOMPOSITION mean SKIN FRICTION TURBULENT channel flow REYNOLDS NUMBER effect
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A survey on numerical simulations of drag and heat reduction mechanism in supersonic/hypersonic flows
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作者 Xiwan SUN Wei HUANG +2 位作者 Min OU Ruirui ZHANG Shibin LI 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第4期771-784,共14页
Along with the survey on experimental investigations drawing attention to the drag and heat reduction mechanism, the authors simultaneously focus on the recent advances of numerical simulations on the schemes applied ... Along with the survey on experimental investigations drawing attention to the drag and heat reduction mechanism, the authors simultaneously focus on the recent advances of numerical simulations on the schemes applied to supersonic/hypersonic vehicles. The CFD study has evolved as an irreplaceable method in scheme evaluation and aircraft optimization. Similar to our previous experimental survey, the advances in drag and heat reduction schemes are reviewed by similar kinds of mechanism in this article, namely the forward-facing cavity, the opposing jet, the aerospike, the energy deposition and their combinational configurations. This review article puts an emphatic eye on the flow conditions, numerical methods, novel schemes and analytical conclusions given in the simulations. Further, the multi-objective design optimization concept has also been illustrated due to the observable advantages of using CFD over experimental method, especially those performances conducted in drag reduction and thermal protection practice, and this would possess reference value in the design of aircraft system. 展开更多
关键词 Aerospike Drag and HEAT reduction Energy DEPOSITION Forward-facing CAVITY Opposing jet
Study of flow characteristics within randomly distributed submerged rigid vegetation 预览
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作者 Paromita Chakraborty Arindam Sarkar 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期358-367,共10页
Flow through submerged rigid vegetation has been studied both analytically and experimentally.The Reynolds stress,present in the governing equation,has been modeled using one of the turbulent stress equations,adopted ... Flow through submerged rigid vegetation has been studied both analytically and experimentally.The Reynolds stress,present in the governing equation,has been modeled using one of the turbulent stress equations,adopted in numerous cases.The adva ntage of this turbulent stress model is to replace the mixing length non linear term of the stress with a linear relatio n between stress and the velocity gradient.The velocity field and shear stress are obtained by solving the governing force balance equation numerically.A correlation,validated with the experimental results,has been developed for the relevant non-dimensional numbers. 展开更多
关键词 SUBMERGED VEGETATION REYNOLDS stress drag force STREAM WISE velocity
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怪自何来?——《点石斋画报》的志怪图像阐释及其跨文化属性
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作者 杨慧丹 《美术》 CSSCI 北大核心 2019年第3期95-100,共6页
在《点石斋画报》这样一份新闻画报中,存在着相当数量的志怪图像,这些充满迷信味道甚至略显愚昧的内容长期以来广受诟病。本文以画报中的《西人见龙》为切入点,将志怪图像置入19世纪中西图像交流的视野中进行图像阐释,尝试讨论两个问题... 在《点石斋画报》这样一份新闻画报中,存在着相当数量的志怪图像,这些充满迷信味道甚至略显愚昧的内容长期以来广受诟病。本文以画报中的《西人见龙》为切入点,将志怪图像置入19世纪中西图像交流的视野中进行图像阐释,尝试讨论两个问题:志怪图像荒诞不经的背后是否另有其意?是什么样的历史语境孕育了这类图像? 展开更多
关键词 点石斋画报 志怪图像 晚清 海怪
Numerical study of the turbulent channel flow under space-dependent electromagnetic force control at different Reynolds numbers 预览
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作者 Daiwen JIANG Hui ZHANG +3 位作者 Baochun FAN Zijie ZHAO Jian LI Mingyue GUI 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第4期435-448,共14页
In this paper,the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with the direct numerical simulation(DNS)methods for different Reynolds... In this paper,the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with the direct numerical simulation(DNS)methods for different Reynolds numbers.A formulation is derived to express the relation between the drag and the Reynolds shear stress.With the application of optimal electromagnetic force,the in-depth relations among characteristic structures in the flow field,mean Reynolds shear stress,and the effect of drag reduction for different Reynolds numbers are discussed.The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers.The regular quasi-streamwise vortex structures,which appear in the flow field,have the same period with that of the electromagnetic force.These structures suppress the random velocity fluctuations,which leads to the absolute value of mean Reynolds shear stress decreasing and the distribution of that moving away from the wall.Moreover,the wave number of optimal electromagnetic force increases,and the scale of the regular quasi-streamwise vortex structures decreases as the Reynolds number increases.Therefore,the rate of drag reduction decreases with the increase in the Reynolds number since the scale of the regular quasi-streamwise vortex structures decreases. 展开更多
关键词 FLOW control drag reduction ELECTROMAGNETIC FORCE TURBULENT channel FLOW
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Two-point statistics of coherent structures in turbulent flow over riblet-mounted surfaces 预览
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作者 Weipeng Li Hong Liu 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第3期457-471,共15页
Direct numerical simulations (DNS) of turbulent flow over a drag-reducing and a drag-increasing riblet configuration are performed. Three-dimensional two-point statistics are presented for the first time to quantify t... Direct numerical simulations (DNS) of turbulent flow over a drag-reducing and a drag-increasing riblet configuration are performed. Three-dimensional two-point statistics are presented for the first time to quantify the interaction of the riblet surfaces with the coherent, energy-bearing eddy structures in the near-wall region. Results provide statistical evidence that the averaged organization of the streamwise vortices in the drag-reducing case is lifted above the riblet tip, while in the drag-increasing case the streamwise vortices are embedded further into the riblet cove. In the spanwise direction, the cores of the streamwise vortices over the riblet surfaces are shown to be closer to each other than those for flow over the smooth wall, and wider riblet spacing leads to more reduction on their spanwise distances. In the cases with riblets the streamwise vortices have longer streamwise lengths, but their inclination angles do not change much. 展开更多
关键词 TURBULENT drag reduction RIBLETS COHERENT structures
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Numerical and experimental research of flow control on an NACA 0012 airfoil by local vibration 预览
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作者 Bin LOU Shangjun YE +1 位作者 Gaofeng WANG Zhilong HUANG 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第1期1-12,共12页
A flow control technique by local vibration is proposed to improve the aerodynamic performance of a typical airfoil NACA 0012.Both wind-tunnel experiments and a large eddy simulation(LES)are carried out to study the e... A flow control technique by local vibration is proposed to improve the aerodynamic performance of a typical airfoil NACA 0012.Both wind-tunnel experiments and a large eddy simulation(LES)are carried out to study the effects of local vibration on drag reduction over a wide range of angles of attack.The application parameters of local vibration on the upper surface of the airfoil are first evaluated by numerical simulations.The mounted position is chosen at 0.065-0.09 of chord length from the leading edge.The influence of oscillation frequency is investigated both by numerical simulations and experiments.The optimal frequencies are near the dominant frequencies of shear layer vortices and wake vortices.The patterns of shear vortices caused by local vibration are also studied to determine the drag reduction mechanism of this flow control method.The results indicate that local vibration can improve the aerodynamic performance of the airfoil.In particular,it can reduce the drag by changing the vortex generation patterns. 展开更多
关键词 LOCAL VIBRATION AIRFOIL VORTEX CONTROL drag REDUCTION
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基于熵产分析的二维运动体自然超空化计算 预览
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作者 汤冬冬 吕续舰 +1 位作者 运洪禄 陈少松 《兵器装备工程学报》 CAS 北大核心 2019年第5期241-246,共6页
基于均质平衡多相流理论,采用有限体积法对二维运动体自然超空化流动进行数值模拟;首先通过基于阻力和熵产的计算网格数量和壁面y+独立性分析,对计算模型进行了确认;随后计算了运动体在不同空化数下的空化流动,将得到的阻力系数和空泡... 基于均质平衡多相流理论,采用有限体积法对二维运动体自然超空化流动进行数值模拟;首先通过基于阻力和熵产的计算网格数量和壁面y+独立性分析,对计算模型进行了确认;随后计算了运动体在不同空化数下的空化流动,将得到的阻力系数和空泡尺寸与文献计算结果和实验结果进行了比较,验证计算模型的准确性;最后,从能量守恒的角度出发,考虑阻力做功为一个不可逆熵产过程,通过流场熵产与阻力之间的联系探索一种用于流动阻力评估的新思路;计算结果表明:在非空化、局部空化、超空化的不同来流速度条件下,阻力和流场的熵产呈分段线性关系,即流场熵产分析可以用来评估二维运动体阻力。 展开更多
关键词 计算流体力学 自然超空泡 熵产 阻力 空泡形态
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Non-Stokes drag coefficient in single-particle electrophoresis:New insights on a classical problem
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作者 廖麦嘉 魏名佐 +2 位作者 徐士鑫 歐陽新喬 沈平 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第8期201-211,共11页
We measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field,and found it to be markedly different from that of the Stoke... We measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field,and found it to be markedly different from that of the Stokes drag.The drag coefficient,along with the measured electrical force,yield a mobility-zeta potential relation that agrees with the literature.By using the measured mobility as input,numerical calculations based on the Poisson-Nernst-Planck equations,coupled to the Navier-Stokes equation,reveal an intriguing microscopic electroosmotic flow near the particle surface,with a well-defined transition between an inner flow field and an outer flow field in the vicinity of electric double layer’s outer boundary.This distinctive interface delineates the surface that gives the correct drag coefficient and the effective electric charge.The consistency between experiments and theoretical predictions provides new insights into the classic electrophoresis problem,and can shed light on new applications of electrophoresis to investigate biological nanoparticles. 展开更多
关键词 ELECTROPHORESIS drag coefficient VORTICES belt CHARGED COLLOIDAL particle
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