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Effects of Rigid Vegetation on the Turbulence Characteristics in Sediment-Laden Flows 被引量:1
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作者 Shengqi Lu Jieren Chen 《Journal of Applied Mathematics and Physics》 2014年第12期1091-1098,共8页
The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow wi... The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction. 展开更多
关键词 RIGID VEGETATION turbulence characteristics Sediment-Laden flow EXPERIMENTAL Study
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Impact of depth ratio on flow structure and turbulence characteristics of compound open channel flows
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作者 Shao-wei Ding Cheng Zeng +2 位作者 Jie Zhou Ling-ling Wang Chen Chen 《Water Science and Engineering》 EI CAS CSCD 2022年第3期265-272,共8页
Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows... Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region. 展开更多
关键词 Large eddy simulation Compound open channel Depth ratio flow structure turbulence characteristics
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Turbulence Characteristics of Swirling Reacting Flow in a Combustor with Staged Air Injection
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作者 张健 普勇 周力行 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2006年第5期634-641,共8页
This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the seco... This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secon-dary non-swirling jet. A three dimension-laser particle dynamic analyzer (PDA) was employed to measure the in-stantaneous gas velocity. The probability density functions (PDF) for the instantaneous gas axial and tangential ve-locities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are ob-tained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion. 展开更多
关键词 swirling reacting flow staged combustion turbulence characteristics
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Turbulence,aeration and bubble features of air-water flows in macro-and intermediate roughness conditions 被引量:2
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作者 Stefano PAGLIARA Thendiyath ROSHNI Iacopo CARNACINA 《Water Science and Engineering》 EI CAS 2011年第2期170-184,共15页
Free surface flows aeration potential causing the in macro- and intermediate flow characteristics to vary roughness conditions have a high with slopes and discharges. The underlying mechanism of two-phase flow charact... Free surface flows aeration potential causing the in macro- and intermediate flow characteristics to vary roughness conditions have a high with slopes and discharges. The underlying mechanism of two-phase flow characteristics in macro- and intermediate roughness conditions were analyzed in an experimental setup assembled at the Laboratory of Hydraulic Protection of the Territory (PITLAB) of the University of Pisa, Italy. Crushed angular rocks and hemispherical boulders were used to intensify the roughness of the bed. Flow rates per unit width ranging between 0.03 m^2/s and 0.09 m^2/s and slopes between 0.26 and 0.46 were tested over different arrangements of a rough bed. Analyses were mainly carried out in the inner flow region, which consists of both bubbly and intermediate flow regions. The findings revealed that the two-phase flow properties over the rough bed were much affected by rough bed arrangements. Turbulence features of two-phase flows over the rough bed were compared with those of the stepped chute data under similar flow conditions. Overall, the results highlight the flow features in the inner layers of the two-phase flow, showing that the maximum turbulence intensity decreases with the relative submergence, while the bubble frequency distribution is affected by the rough bed elements. 展开更多
关键词 turbulent flow aeration characteristics BOULDER macro- and intermediate roughness correlation analysis two-phase flow
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Dynamic Characteristics of High-speed Water-Lubricated Spiral Groove Thrust Bearing Based on Turbulent Cavitating Flow Lubrication Model 被引量:1
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作者 Xiaohui Lin Shun Wang +1 位作者 Shuyun Jiang Shaowen Zhang 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2022年第1期91-111,共21页
The water-lubricated bearings are usually the state of turbulent cavitating flow under high-speed conditions. And the distribution of cavitation bubbles and the interface effect between the two phases have not been in... The water-lubricated bearings are usually the state of turbulent cavitating flow under high-speed conditions. And the distribution of cavitation bubbles and the interface effect between the two phases have not been included in previous studies on high-speed water-lubricated bearings. In order to study the influence of interface effect and cavitation bubble distribution on the dynamic characteristics of high-speed water-lubricated spiral groove thrust bearings(SGTB).A turbulent cavitating flow lubrication model based on two-phase fluid and population balance equation of bubbles was established in this paper. Stiffness and the damping coefficients of the SGTB were calculated using the perturbation pressure equations. An experimental apparatus was developed to verify the theoretical model. Simulating and experimental results show that the small-sized bubbles tend to generate in the turbulent cavitating flow when at a high rotary speed, and the bubbles mainly locate at the edges of the spiral groove. The simulating results also show that the direct stiffness coefficients are increased due to cavitation effect, and cross stiffness coefficients and damping coefficients are hardly affected by the cavitation effect. Turbulent effect on the dynamic characteristics of SGTB is much stronger than the cavitating effect. 展开更多
关键词 Spiral groove thrust bearings Water lubrication turbulent lubrication Cavitating flow Dynamic characteristics
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TRPIV measurement of turbulent coherent structures in a drag-reducing flow by polymers
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作者 Xinlei Guan Nan Jiang +1 位作者 Lu Cheng Hao Zhang 《Theoretical & Applied Mechanics Letters》 CAS 2013年第4期40-43,共4页
Fully developed turbulent flow fields with and without polymer solution at the same Reynolds number were measured by time-resolved particle image velocimetry (TRPIV) in a water channel to investigate the mechanism o... Fully developed turbulent flow fields with and without polymer solution at the same Reynolds number were measured by time-resolved particle image velocimetry (TRPIV) in a water channel to investigate the mechanism of drag-reducing solution from the view of coherent structures manipulation. The streamwise mean velocity and Reynolds stress profiles in the solution were compared with those in water. After adding the polymer solution, the Reynolds stress in the near-wall area decreases significantly. The result relates tightly to the decease of the coherent structures' bursting. The spatial topology of coherent structures during bursts has been extracted by the new mu-level criterion based on locally averaged velocity structure function. The effect of polymers on turbulent coherent structures mainly reflects in the intensity, not in the shape. In the solution, it is by suppressing the coherent structures that the wall friction is reduced. 展开更多
关键词 spatial topology of coherent structures turbulent drag-reducing flow polymer additives TRPIV
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Analysis of the Flow Field Characteristics Associated with the Dynamic Rock Breaking Process Induced by a Multi-Hole Combined External Rotary Bit 被引量:3
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作者 Quanbin Ba Yanbao Liu +2 位作者 Zhigang Zhang Wei Xiong Kai Shen 《Fluid Dynamics & Materials Processing》 EI 2021年第4期697-710,共14页
The characteristics of the flow field associated with a multi-hole combined external rotary bit have been studied by means of numerical simulation in the framework of an RNG k-εturbulence model,and compared with the ... The characteristics of the flow field associated with a multi-hole combined external rotary bit have been studied by means of numerical simulation in the framework of an RNG k-εturbulence model,and compared with the results of dedicated rock breaking drilling experiments.The numerical results show that the nozzle velocity and dynamic pressure of the nozzle decrease with an increase in the jet distance,and the axial velocity of the nozzle decays regularly with an increase in the dimensionless jet distance.Moreover,the axial velocity related to the nozzle with inclination angle 20°and 30°can produce a higher hole depth,while the radial velocity of the nozzle with 60°inclination can enlarge the hole diameter.The outcomes of the CFD simulations are consistent with the actual dynamic rock breaking and pore forming process,which lends credence to the present results and indicates that they could be used as a reference for the future optimization of systems based on the multi-hole combined external rotary bit technology. 展开更多
关键词 External rotation nozzle RNG k-εturbulence model flow field characteristics rock breaking and hole forming process analysis
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Comparison of Flow Characteristics Around Refractive and Right-angled Groins in Barotropic and Baroclinic Conditions
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作者 Omdehghiasi Hamed Mojtahedi Alireza Lotfollahi-Yaghin Mohammad Ali 《Journal of Marine Science and Application》 CSCD 2015年第4期376-388,共13页
Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this stud... Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm's length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow. 展开更多
关键词 refractive groin right-angle groin recirculation area turbulence modeling flow characteristic baroclinic conditions barotropic conditions
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EXPERIMENTAL STUDY ON TURBULENT FEATURES IN THE NEGATIVE TRANSPORT REGION OF ASYMMETRIC PLANE CHANNEL FLOW 被引量:4
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作者 卢志明 刘宇陆 蒋剑波 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2001年第2期125-132,共8页
Turbulent features of streamwise and vertical components of velocity in the negative transport region of asymmetric plane channel flow have been studied experimentally in details. Experiments show that turbulent fluct... Turbulent features of streamwise and vertical components of velocity in the negative transport region of asymmetric plane channel flow have been studied experimentally in details. Experiments show that turbulent fluctuations in negative transport region are suppressed, and their probability distributions are far from Gaussian. Besides, the skewness factors attain their negative maxima at the position of the maximum mean velocity, whereas the flatness factors attain their positive maxima at the same position. 展开更多
关键词 negative transport asymmetric channel flow turbulent characteristics
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Computational Simulation of Turbulent Flow Around Tractor-Trailers 被引量:2
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作者 D.O.Redchyts E.A.Shkvar S.V.Moiseienko 《Fluid Dynamics & Materials Processing》 EI 2020年第1期91-103,共13页
A method to evaluate the properties of turbulent flow in proximity to the vehicle and close to the ground surface has been elaborated.Numerical simulations have been performed on the basis of the Unsteady Reynolds-ave... A method to evaluate the properties of turbulent flow in proximity to the vehicle and close to the ground surface has been elaborated.Numerical simulations have been performed on the basis of the Unsteady Reynolds-averaged Navier-Stokes equations(URANS)written with respect to an arbitrary curvilinear coordinate system.These equations have been solved using the Spalart-Allmaras differential one-parametric turbulence model.The method of artificial compressibility has been used to improve the coupling of pressure and velocity in the framework of a finite volume approach.Time-averaged distributions of pressure fields,velocity components,streamlines in the entire area and near the tractor-trailer,as well as integral and distributed characteristic parameters(such as coefficients of pressure,friction and drag force)are presented.According to our results,the turbulent flow accelerates in the area of the tractor cabin and in the gap between surfaces.Above the driver’s cabin,a pressure drop occurs due to a sharp acceleration of flow in this area.Downstream,pressure is restored and becomes almost constant in proximity to the edge of the trailer.The dimensions of the separation area exceed the length of the transport system several times.Though agreement with experimental results is relatively limited due to the two-dimensional nature of the numerical simulations,the present approach succeeds in identifying the main physical effects involved in the considered dynamics.It might be used in future studies for initial approximate assessments of the influence of the vehicle shape on its aerodynamic characteristics. 展开更多
关键词 High-speed vehicle tractor-trailer turbulent flow ground effect numerical modelling aerodynamic characteristics
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Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence 被引量:1
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作者 蔡伟华 李凤臣 张红娜 《Chinese Physics B》 SCIE EI CAS CSCD 2011年第12期279-292,共14页
Direct numerical simulation of decaying homogeneous isotropic turbulence (DHIT) of a polymer solution is performed. In order to understand the polymer effect on turbulence or additive-turbulence interaction, we dire... Direct numerical simulation of decaying homogeneous isotropic turbulence (DHIT) of a polymer solution is performed. In order to understand the polymer effect on turbulence or additive-turbulence interaction, we directly investigate the influence of polymers on velocity gradient tensor including vorticity and strain. By visualizing vortex tubes and sheets, we observe a remarkable inhibition of vortex structures in an intermediate-scale field and a small-scale field but not for a large scale field in DHIT with polymers. The geometric study indicates a strong relevance among the vorticity vector, rate-of-strain tensor, and polymer conformation tensor. Joint probability density functions show that the polymer effect can increase "strain generation resistance" and "vorticity generation resistance", i.e., inhibit the generation of vortex sheets and tubes, ultimately leading to turbulence inhibition effects. 展开更多
关键词 decaying homogeneous isotropic turbulence turbulent drag-reducing flow velocity gradient tensor direct numerical simulation
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Reaction thrust characteristics of high-pressure submerged water jet of cylinder nozzles 被引量:1
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作者 李晓晖 《Journal of Chongqing University》 CAS 2009年第1期63-69,共7页
The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. T... The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. The simulation of the flow field characteristics was conducted via the FLUENT computational fluid dynamics package. Effects of the inlet conditions and the nozzle dimensions on the reaction thrust of a water jet were addressed particularly. The reaction thrust experiments were performed on a custom-designed test apparatus. The experimental results reveal that a) the nozzle diameter and the inlet conditions exert great influence on the water jet reaction thrust; and b) for L≤4d0, where the nozzle is treated as a thin plate-orifice, the reaction thrust is independent of nozzle length; for L〉4d0, where the nozzle is treated as a long orifice, the reaction thrust can reach maximum under the condition of a certain flow rate. These findings lay a theoretical foundation for the design of nozzles and have significant value, especially for the future development of high-oressure water-let orooulsion technology. 展开更多
关键词 cylindrical nozzle pressure distribution reaction thrust characteristics turbulent flow water jet
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Attenuation analysis of hydraulic transients with laminar-turbulent flow alternations
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作者 万五一 朱嵩 胡云进 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 2010年第10期1209-1216,共8页
An improved compound mathematical model is established to simulate the attenuation of hydraulic transients with laminar-turbulent alternations,which usually occur when the pipeline flow velocity fluctuates near the cr... An improved compound mathematical model is established to simulate the attenuation of hydraulic transients with laminar-turbulent alternations,which usually occur when the pipeline flow velocity fluctuates near the critical velocity.The laminar friction resistance and the turbulent friction resistance are considered respectively in this model by applying different resistance schemes to the characteristics method of fluid transient analysis.The hydraulic transients of the valve closing process are simulated using the model.A more reasonable attenuation of hydraulic transients is obtained.The accurate attenuation is more distinct than that obtained from the traditional mathematical model.The research shows that the hydraulic transient is a type of energy waves,and its attenuation is caused by the friction resistance.The laminar friction resistance is more important than the turbulent friction resistance if the flow velocity is smaller than the critical velocity.Otherwise the turbulent friction resistance is more important.The laminar friction resistance is important in the attenuation of hydraulic transients for the closing process.Thus,it is significant to consider the different resistances separately to obtain more accurate attenuation of hydraulic transients. 展开更多
关键词 fluid transient laminar flow turbulent flow method of characteristics
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簇状分布的刚性双层植被明渠紊流特性分析
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作者 吕升奇 陈俊舟 +1 位作者 陈红 陈界仁 《水利水电科技进展》 CSCD 北大核心 2024年第3期8-12,33,共6页
采用RNG k-ε紊流模型,对簇状分布的刚性双层植被明渠水流进行了模拟和分析;根据时间及空间的双平均方法对植被明渠水流的流速及紊动参数进行了统计。结果表明:簇状分布的植被明渠水流可以分为植物区、间隙区及主流区,不同区域时均流速... 采用RNG k-ε紊流模型,对簇状分布的刚性双层植被明渠水流进行了模拟和分析;根据时间及空间的双平均方法对植被明渠水流的流速及紊动参数进行了统计。结果表明:簇状分布的植被明渠水流可以分为植物区、间隙区及主流区,不同区域时均流速的大小和分布各异;双层植被明渠水流中,时均流速垂线分布在近床面、低植物顶部附近及高植物顶部附近均出现拐点,脉动强度和紊动能的最大值出现在高植物顶部附近。 展开更多
关键词 双层植被 簇状分布 植被明渠水流 紊流特性 紊动能
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TURBULENCE CHARACTERISTICS IN SMOOTH OPEN-CHANNEL FLOW
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作者 董曾南 丁元 《Science China Mathematics》 SCIE 1990年第2期244-256,共13页
A flow in a smooth open channel can he divided into several regions along the flow direction, i. e. the laminar boundary layer, transition region, turbulent boundary layer, fully developed turbulent boundary layer and... A flow in a smooth open channel can he divided into several regions along the flow direction, i. e. the laminar boundary layer, transition region, turbulent boundary layer, fully developed turbulent boundary layer and a uniform open-channel turbulent flow. The temporal mean and turbulent characteristics will not vary again in the course of the uniform open-channel flow. There is obviously a structure of different regions in the vertical direction of a smooth open-channel turbulent flow. The limits of different regions, the velocity profiles and characteristics of fluctuating velocities in such regions are given. When the aspect ratio W/H is larger than 10, the flow in the open channel may be considered as a 2-dimensional flow. The formulas of sectional averaged velocity and frictional loss factor are also given. 展开更多
关键词 open-channel flow turbulence characteristics.
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新型三段式粗颗粒浮选柱内流场数值模拟
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作者 彭建 孙伟 +6 位作者 沈政昌 韩海生 晋应升 肖遥 高志勇 孙磊 罗远家 《中国有色金属学报》 EI CAS CSCD 北大核心 2024年第8期2801-2818,共18页
本文对一种新型三段式粗颗粒浮选柱内流场特性进行了研究,结果表明,稳流板的加入可增强粗颗粒浮选柱内流体的湍动能和湍流耗散率,促进气泡和粗颗粒的相互作用以及湍动能、湍流耗散率和液相速度的均匀分布,从而利于矿化气泡的输送。射流... 本文对一种新型三段式粗颗粒浮选柱内流场特性进行了研究,结果表明,稳流板的加入可增强粗颗粒浮选柱内流体的湍动能和湍流耗散率,促进气泡和粗颗粒的相互作用以及湍动能、湍流耗散率和液相速度的均匀分布,从而利于矿化气泡的输送。射流管个数的增加使粗颗粒浮选柱内湍动能和湍流耗散率分布趋向于均匀。对称的4个射流管可显著改善流场分布,形成的漩涡促进了气泡与颗粒的相互作用,稳流板使气泡速度分布均匀。浮选柱内湍动能随着上升水量和充气量的增加而增大,稳流板作用明显。上升水量对稳流板上下方区域湍流耗散率的影响呈梯级分布,可实现底部紊流矿化、中部紊流−稳流转变、上部静态流态化浮选的三段式流体环境,利于粗颗粒矿物浮选的回收。 展开更多
关键词 浮选柱 流场特性 湍动能 湍流耗散率 计算流体动力学
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气固两相湍流非定常压力脉动特性数值模拟研究
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作者 阳勇 臧雯雯 +1 位作者 韩省思 毛军逵 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2024年第3期311-324,共14页
与发动机振荡燃烧相关的气固两相流中的压力脉动现象长期以来备受关注。为了解发动机气固两相流动中的非定常压力脉动特性,以典型的后台阶气固两相流动为研究对象,使用发展的自适应湍流模拟(Self-adaptive turbulence eddy simulation,S... 与发动机振荡燃烧相关的气固两相流中的压力脉动现象长期以来备受关注。为了解发动机气固两相流动中的非定常压力脉动特性,以典型的后台阶气固两相流动为研究对象,使用发展的自适应湍流模拟(Self-adaptive turbulence eddy simulation,SATES)和离散相模型(Discrete phase model,DPM)相结合的方法,对两相流场进行了三维非定常高精度数值计算。以实验数据作为参考验证了计算方法的精度和可靠性。通过将两相流场的压力脉动信号与纯气相流场进行对比,发现加入颗粒后流场压力脉动主导频率略有变化,无量纲压力脉动幅值明显减小;进一步研究了固体颗粒直径和质量分数对脉动特性的影响规律,发现随着颗粒直径变大,流场振幅先减小后增大。颗粒直径为10μm时,振幅最小;随着质量分数的增大,流场振幅呈现出下降趋势。研究表明气固两相流中颗粒的参数变化对振荡主频影响较小,对脉动振幅影响显著。 展开更多
关键词 压力脉动 后台阶气固两相流 自适应湍流模拟 离散相模型 频谱特性
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粗糙床面坡面流流场及紊动特性试验研究
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作者 季铭昱 程年生 《泥沙研究》 CAS CSCD 北大核心 2024年第2期41-47,共7页
应用粒子图像测速技术对水深为5~8 mm的粗糙床面坡面流流场进行了详细观测,对试验资料进行了时间-空间双平均处理,结果表明:在低淹没度的床面糙率影响下,坡面流流速分布基本符合对数-尾流规律,其中卡门常数与普通明渠流一致,但尾流函数... 应用粒子图像测速技术对水深为5~8 mm的粗糙床面坡面流流场进行了详细观测,对试验资料进行了时间-空间双平均处理,结果表明:在低淹没度的床面糙率影响下,坡面流流速分布基本符合对数-尾流规律,其中卡门常数与普通明渠流一致,但尾流函数常数明显偏小;相较于光滑床面,粗糙元增强了水流流向的紊动强度,同时致使紊动强度在水深范围内的分布更趋均匀;水流切应力分布以雷诺切应力为主导,粗糙元引起的形状切应力可以忽略不计;水流的空间波动主要存在于床面附近,但流速的空间波动强度与紊动强度相比普遍偏小。 展开更多
关键词 坡面流 粗糙床面 流速分布 紊动特性 PIV 时间-空间双平均
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Arc Voltage Fluctuation in DC Laminar and Turbulent Plasma Jets Generation 被引量:3
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作者 潘文霞 孟显 吴承康 《Plasma Science and Technology》 SCIE EI CAS CSCD 2006年第4期416-421,共6页
Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view tow... Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current (AC) component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc. 展开更多
关键词 DC plasma jet fluctuation characteristics laminar flow turbulent flow experimental study
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Analysis of pressure characteristics under laminar and turbulent flow states inside the pilot stage of a deflection flapper servo-valve:Mathematical modeling with CFD study and experimental validation 被引量:8
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作者 Bijan Krishna SAHA Songjing LI Xinbei LV 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2020年第3期1107-1118,共12页
Electro-hydraulic servo-valves are widely used components in the mechanical industry,aerospace and aerodynamic devices which precisely control the airplane or missile wings.Due to the small size and complex structure ... Electro-hydraulic servo-valves are widely used components in the mechanical industry,aerospace and aerodynamic devices which precisely control the airplane or missile wings.Due to the small size and complex structure in the pilot stage of deflection flapper servo-valves,accurate mathematical models for the flow and pressure characteristics have always been very difficult to be built.In this paper,mathematical models for the pilot stage of deflection flapper servo-valve are investigated to overcome some gaps between the theoretical formulation and overall performance of the valve by considering different flow states.Here,a mathematical model of the velocity distribution at the flapper groove exit is established by using Schlichting velocity equations for incompressible laminar fluid flow.Moreover,when the flow becomes turbulent,a mathematical model of pressure characteristics in the receiving ports is built on the basis of the assumption of the collision between the liquid and the jet as the impact of the jet on a moving block of fluid particles.To verify the analytical models for both laminar and turbulent flows,the pressure characteristics of the deflection flapper pilot stage are calculated and tested by using numerical simulation and experiment.Experimental verification of the theory is also presented.The computed numerical and analytical results show a good agreement with experimental data. 展开更多
关键词 Computational fluid dynamics(CFD) Deflection flapper servovalve Laminar flow Pressure characteristics Servo-valve turbulent submerged jet
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