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1.
正方体人工鱼礁流场效应试验研究   总被引:4,自引:0,他引:4  
刘彦  赵云鹏  崔勇  董国海 《海洋工程》2012,30(4):103-108
采用无干扰的粒子图像测速技术(PIV),针对中空型正方体人工鱼礁,选取3个不同的来流速度6.7 cm/s、11.0 cm/s和18.0 cm/s,研究了该模型单体(90°和45°)和组合(平行和垂直)工况时的流场效应。结果显示,单体90°迎流时上升流的规模和强度大于45°迎流,但产生的缓流区和背涡流的规模远小于45°工况。横向组合中单个鱼礁模型产生的流场效应较强于单体工况。纵向组合中,第一个迎流鱼礁在不同间距时内部流速分布和单体时较为相似,间距为1.0L时流速大小与单体最为接近。第二个迎流鱼礁内部基本上未出现回流区域,水平流速较单体时明显减小,但随着间距的增加流速值不断增大。  相似文献
2.
-Force measurements of oscillatory flow acting on a single circular cylinder have been carriedout.The experiments were done by oscillating a circular cylinder in still water.Instantaneous forces and ve-locity fields around the cylinder were measured by Particle Image Velocimetry(PIV).The Keulegan-Car-penter number(KC)varied in the range from 5 to 20 and the viscous parameter β=Re/KC was set at500(Re is Reynolds number).It was found that the strength and frequency of the lift force increased withKC number,the main frequency of the lift force being three times the frequency of the oscillatory flow atKC=20.The movement and strength of the vortices around the cylinder are discussed for differentKC numbers.  相似文献
3.
粗糙地形对内波生成影响的实验研究   总被引:1,自引:1,他引:0       下载免费PDF全文
王金虎  陈旭  徐洋 《海洋与湖沼》2016,47(4):706-713
为了研究粗糙地形对内波共振生成的影响,本文在实验中采用粒子图像测速法(PIV)对内波速度场进行测量。实验中设置了两种不同尺度的粗糙地形,其中一种地形的粗糙尺度大于黏性边界层厚度(δ),另一种地形的粗糙尺度小于δ。结果表明两种粗糙地形都使共振内波的能量减弱,粗糙地形一侧生成的内波强度约为光滑地形一侧生成内波强度的40%。当粗糙地形的尺度大于δ时,在粗糙地形一侧除了共振内波以外还有明显的内波射线生成,粗糙地形上的每一个凸形间断点都成为了一个新的内波源点,每条内波射线的强度约为共振内波强度的1/10,由新源点生成的内波射线相位基本一致,落后于正压潮3π/5个相位。当粗糙地形的尺度小于δ时,粗糙地形一侧仅有共振内波生成,共振内波的相位与正压潮相位十分接近。  相似文献
4.
X.K. Wang  S.K. Tan 《Ocean Engineering》2008,35(5-6):458-472
The flow patterns in the near wake of a cylinder (either circular or square in shape, D=25 mm) placed in the proximity of a fully developed turbulent boundary layer (thickness δ=0.4D) are investigated experimentally using particle image velocimetry (PIV). The effects of changing the gap height (S) between the cylinder bottom and the wall surface, over the gap ratio range S/D=0.1–1.0, have been investigated. The results show that both the ensemble-averaged and instantaneous flow fields are strongly dependent on S/D. The flow patterns for the two types of cylinders share many similarities with respect to the change in S/D, such as the reduced recirculation length and increased velocity fluctuation in the near wake with increasing S/D, as well as the trend of suppression of vortex shedding at small S/D and onset of vortex shedding at large S/D. However, developments of the shear layers, in terms of wake width, flow curvature, etc., are considerably different for these two types of cylinders. In general, the wake development and momentum exchange for the square cylinder are slower those for the circular cylinder at the same gap ratio. Correspondingly, it is shown that the periodic vortex shedding is delayed and weakened in the case of square cylinder, as compared to that of the circular cylinder at the same S/D.  相似文献
5.
The characteristics of the flow over the rudder’s pintle gap are investigated by using the particle image velocimetry (PIV) technique. The propeller and rudder models are scaled down to 1/28.5. Highly accelerated leakage outflows are separated at the discontinuities of the gap and generate strong cavitation at the suction side of the rudder. In the rudder and propeller configuration, the propeller wake sheet ahead of the gap entrance region starts to induce leakage flow over the lower pintle gaps of the suction side. The gap flow has a velocity magnitude as high as 0.4U0 in the high leakage flow condition, where the wake sheet locates over the gap entrance. The cross-flow of the propeller wake sheet interferes the gap entrance region and triggers gap cavitation. As the propeller wake sheet moves downstream and weakens, the gap flow velocity decreases over the gap entrance.  相似文献
6.
为研究幂律流体偏心环空螺旋流轴向速度的分布规律,建立了幂律流体的偏心垂直环空螺旋流动实验模型及实验方案。利用PIV系统拍摄各种工况下偏心环空螺旋流场中粒子的图像,对实验数据进行处理分析,确定了幂律流体偏心环空螺旋流轴向速度分布的主要影响因素。着重分析了压力梯度、黏滞性、内管旋转角速度、偏心度这些影响因素对偏心环空宽、窄间隙处轴向速度分布的影响规律,为解决石油工业中相关问题提供了有益的参考。  相似文献
7.
深水防波堤周围流场存在复杂的紊动变化,防波堤较容易发生失效破坏。本文利用PIV技术,基于模型实验,对规则波作用下防波堤周围的速度流场及其涡流特性进行了实验研究,获得了规则波流场的瞬时速度分布。通过对不同型式防波堤在不同的水力条件下的波浪流场实验数据的分析,定量地研究了防波堤堤身水域的涡旋流场的水力特性。  相似文献
8.
The purpose of this paper is to investigate the instantaneous properties of wave slamming on the plate structure of an open structure.The advanced instantaneous measuring technique-Particle Image Velocimetry(PIV) is applied to acquire the instantaneous velocity field of wave slamming.From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis.  相似文献
9.
The instantaneous turbulent velocity field produced by a broken solitary wave propagating on a 1 in 50 plane slope was measured in the longitudinal transverse plane in the middle part of the water column and near the bottom using a stereoscopic particle image velocimetry system. These measurements showed that large-scale turbulence first arrived in the form of a downburst of turbulent fluid. In the middle of the water column, the downbursts arrived shortly after the wave crest had passed. Each downburst was accompanied by two counter-rotating vortices. The latter grew rapidly in size to become a prominent feature of the flow field. Each vortex had a typical length scale of 1/2 to 1 water depth, and carried most of the turbulent kinetic energy in the region between the vortices. Near the bottom, the counter-rotating vortices were not as well defined and covered only a small plane area compared to the entire flow structure. The turbulent fluid descending from above diverged at the bed and the resulting flow structure developed an elongated shape as the source of down-flow travelled onshore with the broken wave. It was found that the transverse spacing between adjacent downbursts ranged from 2 to 5 times the local still water depth. Since vortices cannot end in the interior of the fluid, the counter-rotating vortices must extend to the free surface in the form of a vortex loop. It was suggested that these vortex loops were produced by bending and stretching of primary vorticity generated in the wave breaking process, possibly as a result of three-dimensional water surface deformation. The vortex loops were then carried downward by the falling water from the broken wave.  相似文献
10.
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