共查询到18条相似文献,搜索用时 171 毫秒
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[目的]为探讨近壁旋转圆柱尾流及流体力特性,对典型间隙比下旋转圆柱绕流进行研究。[方法]对雷诺数Re=200下3种典型间隙比(G/D=0.2,0.8,1.4)的旋转圆柱绕流展开数值模拟,对比不同间隙比和转速比下的圆柱尾流及流体力特性。[结果]结果显示:当G/D=0.2时,圆柱表面脱涡会受到显著抑制,圆柱表面升阻力无波动;当G/D=0.8和1.4且转速比较低时,会发生“尾流涡”脱落现象,其结构与2S模式相似,升阻力系数呈正弦周期性波动,振幅较小;当正旋转速较大时,圆柱表面无漩涡脱落,形成稳定的D模式尾流(随转速比增大由D+模式变为D-模式),“尾流涡层”与“壁面涡层”发生分离,“壁面涡”呈现多周期性脱落现象,升阻力系数呈多周期波动,振幅显著增大;当反旋转速较大时,圆柱表面被一层正涡量的涡层包裹,漩涡脱落受到显著抑制,升阻力无波动。[结论]所得结论可为高效流动控制技术发展提供参考。 相似文献
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基于浸没边界-多松弛-格子玻尔兹曼方法,对Re=100时等边三角形布置三圆柱体群绕流问题进行数值模拟,分析间距比(Kd)与来流角度(α)两个关键参数对流体力系数及流场特性的影响,揭示其流动机理。计算结果表明:不同流场下尾流模式分为单漩涡、单漩涡体向双漩涡过渡、不规则的双漩涡、规则的双漩涡、双漩涡向三漩涡过渡、不规则的三漩涡和规则的三漩涡模式,在α=30°时流场下游涡街更加规则,尾流模式转变更快。三圆柱所受的时均流体力系数受间隙流流速影响较大,各来流角度下随间距比(除小间距比外)的变化趋势基本一致,尾流模式转变会导致三圆柱群的流体力系数均方根值发生显著变化,在Kd≥3.5后上游圆柱流体力系数均方根值有较大起伏。除α=0°工况外,在Kd≥2.5后中游圆柱的涡脱落频率受α和Kd影响较小,数值相对稳定。 相似文献
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风力转子推进装置节能环保,降低推力成本,有利于船舶行业的绿色发展。基于多松弛格子Boltzmann方法,对并列风力助推转子绕流进行数值模拟。首先模拟单圆柱绕流的流动特性,以验证程序的可靠性,重点探究双圆柱的间距比和转速比对圆柱绕流特性的影响。获取圆柱的升阻力系数以及尾流流型,验证临界转速比的存在。结果显示:旋转可以有效地抑制涡的生成和脱落,当转速比达到临界转速比时,漩涡彻底消失,流场变得稳定;时均升力系数的绝对值和时均阻力系数随转速比的增大分别增大和减小。 相似文献
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格子Boltzmann方法在串列双圆柱绕流数值模拟中的应用研究 总被引:1,自引:0,他引:1
基于格子Boltzmann方法,对二维静止串列双圆柱绕流进行了数值模拟,并将模拟结果与已有研究结果进行了对比分析。为提高计算效率和计算精度,采用了多块网格耦合算法,并在圆柱曲边界处采用了较为精确的边界处理方法。提取了圆柱的升阻力系数,讨论了圆柱间距对圆柱受力情况和尾流特征的影响。数值模拟在雷诺数Re=200条件下进行,对两圆柱中心间距为1.5~4.0D(D为圆柱直径)之间的典型间距进行了数值模拟,获得了圆柱升阻力系数以及尾流中涡和流线的变化,验证了临界间距的存在,模拟结果和已有研究结果符合得较好。 相似文献
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The vortex-induced vibrations (VIV) of two flexible circular cylinders in a tandem configuration were studied numerically for spacing ratios ranging from 6 to 18 and the reduced velocities ranging from 2.35 to 12.59. The VIV response amplitude, response frequency, fluid force, pressure distribution and vortex structure of the tandem cylinders with different spacing ratios under different reduced velocities were compared. The results indicate that there is a great difference between the lift forces on the downstream and upstream cylinders. The lift coefficient of the downstream cylinder undergoing the wake-induced vibrations (WIV) is larger than that of the upstream cylinder, and the dominant frequency curves of the lift coefficients of the upstream and downstream cylinders separate. It can be found that the length and intensity of the wake are quite different under different reduced velocities and spacing ratios, and the reattachment positions between the wake and the downstream cylinder are different, which leads to a great change in the flow around the downstream cylinder and have a great effect on the wake-induced lift force on the downstream cylinder. Considering these factors, an empirical model for the wake-induced lift force on a cylinder with low mass ratio was proposed and verified. 相似文献
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《船舶与海洋工程学报》2017,(3)
Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition. 相似文献
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In this work, experimental investigations have been pursued to analyse the influence of downward seepage on the turbulent characteristics of flow and corresponding changes in vortex structure around circular bridge pier in alluvial channel. Experiments were conducted in sand bed channel with circular piers of different sizes for no seepage, 10% seepage and 20% seepage cases. The measurement of turbulent flow statistics such as velocity and Reynolds stresses is found to be negative within the scour hole at upstream of the pier whereas application of downward seepage retards the reversal of the flow causing a decrement in the velocity and Reynolds stresses. Higher Reynolds shear stress prevails at the downstream side because of the production of wake vortices. Contribution of all bursting events to the total Reynolds shear stress production has been observed to increase with downward seepage. The analysis of integral scale suggest that size of eddies increases with seepage, which is responsible for increase in particle mobility. Initially rate of scouring is more which abatements gradually with expanding time as well as with the increased of downward seepage. Presence of downward seepage reduces the depth and length of vortex and shifts towards downstream side of the pier. 相似文献
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《船舶与海洋工程学报》2017,(1)
In this work, experimental investigations have been pursued to analyse the influence of downward seepage on the turbulent characteristics of flow and corresponding changes in vortex structure around circular bridge pier in alluvial channel. Experiments were conducted in sand bed channel with circular piers of different sizes for no seepage, 10% seepage and 20% seepage cases. The measurement of turbulent flow statistics such as velocity and Reynolds stresses is found to be negative within the scour hole at upstream of the pier whereas application of downward seepage retards the reversal of the flow causing a decrement in the velocity and Reynolds stresses. Higher Reynolds shear stress prevails at the downstream side because of the production of wake vortices. Contribution of all bursting events to the total Reynolds shear stress production has been observed to increase with downward seepage. The analysis of integral scale suggest that size of eddies increases with seepage, which is responsible for increase in particle mobility. Initially rate of scouring is more which abatements gradually with expanding time as well as with the increased of downward seepage. Presence of downward seepage reduces the depth and length of vortex and shifts towards downstream side of the pier. 相似文献
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文章运用半隐式特征线分裂算子有限元算法对串列布置的静止上游柱体和下游圆柱的尾激振动问题进行了数值模拟研究。数值结果表明:上游柱体结构的形状、尺寸比(d/D)和折减速度(Ur)三个参数对下游圆柱体结构的动力响应、运动轨迹与涡脱落模态有着显著的影响,且与单圆柱工况相比存在明显区别;随着尺寸比的增大,上/下游柱体结构之间的互扰作用会由流致效应逐渐转变为尾流效应,使得频率特性发生变化,并会导致下游圆柱体结构的振动响应增强;当d/D=0.5和1.0时,下游圆柱体结构的运动轨迹主要为“8”字形;当d/D=1.5时,除了“8”字形外,运动轨迹还会呈现双弯刀形、“双8”字形和不规则形状。通过对流体力系数与位移时程曲线及位移PSD曲线特性进行分析,揭示了其相互作用的内在机理。另外,下游圆柱体结构的尾流场特性也会随参数的变化而变化,其涡脱落模态主要为2S、P+S和2P三种。 相似文献
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The present study examines scour geometry and turbulent flow characteristics around circular and oblong piers in alluvial channel with downward seepage. Experiments were conducted in plane sand bed of non-uniform sand under no seepage, 10% seepage and 15% seepage conditions. Scour depth at oblong pier is significantly lesser than the scour depth at circular one.However, the scour depth at both piers reduces with downward seepage. The measurements show that the velocity and Reynolds stresses are negative near the bed at upstream of piers where the strong reversal occurs. At downstream of oblong pier near the free surface, velocity and Reynolds stresses are less positive; whereas, they are negative at downstream of circular pier. The streamline shape of oblong pier leads to reduce the strength of wake vortices and consequently reversal flow at downstream of pier. With application of downward seepage turbulent kinetic energy is decreasing. The results show that the wake vortices at oblong pier are weaker than the wake vortices at circular pier. The strength of wake vortices diminishes with downward seepage.The Strouhal number is lesser for oblong pier and decreases with downward seepage for both oblong and circular piers. 相似文献