共查询到20条相似文献,搜索用时 164 毫秒
1.
PIV是近二十年发展起来的一种瞬时、全场的现代流场测试手段,已经在各行各业的流场测量中被广泛应用.对于早期发展的使用自相相关算法的PIV系统,由于其先天的不足,在速度方向上存在180°不确定性.本文提出了一种基于连续性方程解决二维流动PIV测速方向二义性的方法,并使用模拟流场对它进行了检验,同时分析了在实际测量中应用的可行性,分析得出在测量误差小于10%时,本方法是可行的.这为那些存在速度方向二义性问题的PIV系统,在进行二维测量时,解决二义性困难提供了一种经济有效的手段. 相似文献
2.
本文介绍一种PIV与BEM相结合的流场研究方法,PIV(Particle Image Velocimetry)是一种现代流场测试技术,BEM(Boundary Element Method)是一种流行的CFD方法,所谓PIV和BEM相结合的方法,是利用流域内PIV测量的结果和BEM法的反过程估计出边界上洲际流场相关量的值,进而估计出流域内其它点的速度值,这种方法可以很好地修正PIV的测量结果,减小它们的误差,同时还可以对测量失效区域的流场进行估计,增加流场信息,在文中它被应用到楔形体入水的PIV测量后处理中,取得了很好的效果。 相似文献
3.
4.
粒子图像测速(PIV)技术是一种定量的非接触式全局速度场测量技术。在船舶与海洋工程领域,PIV实验中拍摄的粒子图像常出现结构物遮挡或自由液面等干扰现象,需要对其进行掩模后计算液相区域速度场。因此,实现PIV图像中干扰区域自动掩模及液相区域速度场高精度计算具有重要的意义。本文基于光流卷积神经网络LiteFlowNet,设计了一种可实现自动掩模及速度场计算的深度学习模型Mask-PIV-LiteFlowNet,并使用基于物体入水PIV实验图像掩模数据集和PIV速度场计算数据集制作的数据集对其进行训练和测试。测试结果表明,该模型能够有效减少临近掩模边界区域的速度场计算错误并能够精细地提取流场小尺度流动信息,相比于当前先进的PIV深度学习模型PIV-LiteFlowNet-en,本文提出的模型在对带结构物的合成粒子图像进行流场计算时精度获得了至少14.5%的提升,计算速度上获得了5.7%的提升。最后,使用楔形体入水PIV图像对提出的模型进行了测试,验证了模型的泛化能力。 相似文献
5.
6.
7.
通气超空泡内部流场的PIV实验图像处理 总被引:1,自引:0,他引:1
PIV测试是流体动力学实验研究的重要方法之一,可以成为通气超空泡内部流场结构实验研究的有效手段。通过水洞实验利用PIV对通气超空泡内部流场进行测试时,激光在气液两相界面处会发生折射,导致实验图像变形和失真。文章分析了激光在空化流场中各相界面的折射特性和PIV实验图像的变形规律;在此基础上,推导了图像变形的分析计算式,给出了通过原始流场图像获取真实流场图像的还原处理方法;编制了图像还原计算程序,并对原始PIV图像进行了处理,得到了反映真实空泡内部流场结构的图像。 相似文献
8.
9.
10.
11.
Bu Geun Paik Choung Mook Lee Sang Joon Lee 《Journal of Marine Science and Technology》2005,10(3):123-130
In order to investigate the effects of a free surface on the wake behind a rotating propeller, experiments were carried out in a circulating water channel for two cases: one with an open free surface and one with a closed free surface covered by a rigid plate. Four hundred instantaneous velocity fields were measured using a two-frame particle image velocimetry (PIV) technique at four different blade phases. These were ensemble-averaged to investigate the time-averaged flow structure in the near-wake region. For a surface ship, the flow behind the propeller is influenced by the hull wake and the free surface. The phase-averaged mean velocity fields show the potential wake and the viscous wake formed by the boundary layers developed on the blade surfaces. The interaction between the bilge vortices and the incoming flow along the ship’s hull deforms the wake structure. Tip vortices are generated periodically, and the slipstream contraction occurs in the near-wake region. The free surface was found to affect the axial velocity component and vortex structure behind the propeller. As the flow goes downstream, the tip and trailing vortices dissipate due to turbulent diffusion and active mixing with adjacent vortices. 相似文献
12.
13.
14.
15.
Takafumi Kawamura 《Journal of Marine Science and Technology》2000,5(4):161-175
Large-eddy simulations (LES) of the interactions between turbulent shear flow and surface waves are presented. The formation
mechanism of Langmuir circulation and its contribution to the vertical momentum transport are investigated in detail. The
effect of surface waves is modeled in two ways in the LES runs. One model includes only the phase-averaged effect of the waves
as an added source term in the momentum equation, and the other model includes the full effect of the waves by use of the
fully nonlinear conditions of the air-water interface. Langmuir circulations are clearly indicated in both cases, indicating
that the phase-averaged effect is essential for the formation of this circulation. It is shown that the formation of Langmuir
circulations enhances the vertical transport of momentum. As a result, the mean velocity gradient and the streamwise component
of the turbulence intensity are decreased, while the spanwise and interface normal components are increased. Examination of
the turbulence energy budget equations shows that production is due to the interaction between the vorticity and the Lagrangian
drift as the phase-averaged effect of the wave becomes the dominant source of turbulence.
Received: August 17, 2000 / Accepted: December 22, 2000 相似文献
16.
系统地概述了近年来燃气轮机燃烧室测试技术的应用及进展,介绍了激光多谱勒技术,粒子图象速度技术、激光荧光法和剌曼光谱测温技术的原理和特点,以及目前有关湍流火焰火焰前峰厚度及温度梯度的定量测试分析的报道。 相似文献
17.
The main purpose of this investigation was to demonstrate a useful application of the particle image velocimetry (PIV) method to analyze the complex flow characteristics around a ship. For a sample illustration, the KRISO 3600TEU container ship model was chosen. The flow structure in the stern and near-wake region of the model has been investigated experimentally in a circulating water channel. Instantaneous velocity fields measured by the PIV velocity field measurement technique have been ensemble-averaged to give details of flow structures such as the spatial distributions of the local mean velocity, vorticity, and turbulent kinetic energy. The free-stream velocity was fixed at U
o = 0.6m/s, and the corresponding Reynolds number based on the length between perpendiculars was about 9.0 × 105. The container ship model shows a complicated three-dimensional flow structure in the stern and near-wake regions. The PIV results clearly revealed the formation of large-scale bilge vortices in the stern region and their effect on the flow in the near-wake. The results shown here provide valuable information for hull form design and the validation of viscous ship flow codes and of turbulence models. 相似文献
18.
19.