共查询到17条相似文献,搜索用时 156 毫秒
1.
对槽道内涡波流场的瞬态速度矢量场进行了2DPIV测量实验,将2DPIV测量的矢量场数据进行POD分析,根据POD分解的各阶模态的能量比确定了表征涡波流场主导结构的前15阶模态。结果表明,POD分解的前15阶模态发现槽道内涡波流场是由槽道壁面剪切层诱导的涡列以及伴随的波状主流组成;流场中大尺度的涡旋发展为涡对,对波状主流的脉动频率产生影响;根据涡波流场中的驻点和鞍点,获取了流场的大尺度涡对、平均流场以及Helmholtz涡环等明显特征;最后根据POD分解的前15阶模态对槽道内涡波流场进行重组,重组流场表征了槽道内层流状态下波状主流的形态和涡旋共存的涡波结构以及驻点和鞍点的位置处涡旋的变化等主要特征,有效地剔除了PIV测量流场中的随机信息,保留了PIV测量流场的主导特征。 相似文献
2.
非对称槽道中涡旋波的特性研究 总被引:3,自引:0,他引:3
利用PIV流场显示技术,对振荡流体在非对称槽道中涡旋波的产生、发展和消失的规律进
行了实验研究和分析,测得了涡旋波流场的速度矢量图,阐明了涡旋波流场周期性变化的特
点. 结合涡动力学方程,深入分析并揭示了做周期性运动的流体能在槽道中产生波的特性这
一规律,从中发现:流体周期变化的非定常性和不对称的槽道结构是形成涡旋波流动的主要
因素. 本文对涡旋波流场中各个旋涡的速度分布和涡量进行了测量和计算,分析了涡旋波
强化传质的机理,并研究了Re数对涡旋波流动的影响 相似文献
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槽道湍流近壁结构的DPIV观测实验 总被引:1,自引:0,他引:1
采用DPIV系统(由两台CCD相机组成)对槽道湍流进行速度场时间历程的观测实验,通
过对大量测量结果的综合分析,取得了槽道湍流近壁结构的空间结构及其时间演化过程特征
的结果,可以揭示上扫下掠、湍流瞬时速度型等现象与大尺度涡演化的物理关系,解释若干
湍流大尺度结构的特征机理,还表明DPIV系统提供了一种定量观测湍流的时空结构特征的手
段. 相似文献
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PIV速度场坏矢量的本征正交分解处理技术 总被引:1,自引:0,他引:1
介绍了一种针对粒子图像测速(PIV)基于本征正交分解(POD)的速度场后处理技术.该技术改变了现在后处理技术将速度场坏矢量识别和修正分开实现的局面,通过迭代方法有效地实现了速度场坏点统一的识别和修复算法.算法利用POD分解的低阶模态信息重构出可以用于坏矢量识别的参考速度场,利用该参考速度场对全流场进行坏点识别并完成修正.通过对一套光滑的PIV速度场数据引入高斯分布的随机误差,测试验证了该POD方法的优越性.在坏矢量识别方面新方法较归一化中值检验有更高的正确性,能识别大面积出现的坏矢量区域.在坏矢量修补的插值算法中,新方法的计算效率又高于传统Gappy POD方法,且计算精度优于常见的矢量场内插数学方法.特别是在数据缺失的大连通区域,该方法对物理流场有很好的预测效果. 相似文献
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竖直平板间自然对流大尺度相干结构的POD分析 总被引:5,自引:0,他引:5
POD方法是研究湍流相干结构的有效手段.将该方法应用于竖直平板间自然对流的问题,考虑到流场的热耦合性,采取了速度场与温度场相关联的POD分析.研究表明,该流场具有显著的结构性,流场中的主要含能流动形态为大尺度螺旋涡与纵向涡结构.用POD分析方法,得到广义“能量”在各模态问的分布,发现其分布有比较明显的收敛性.通过POD方法重构流场,可以用较少的模态捕捉到该流场的主要信息. 相似文献
9.
针对高超声速通气模型内阻测量存在的误差大的问题,首次采用DPIV技术和总压测量排架相结合的方法测量了超燃发动机尾喷管流场速度矢量和皮托压力分布,间接获得了内流出口处平均马赫数和静压平均值,从而实现了高超声速通气模型内阻测量。研究结果表明:DPIV试验获得的粒子图像可以清楚地显示喷管出口位置内外流的分界面、内外流混合层的尾迹、通气模型外表面边界层;DPIV试验获得的速度矢量场结果准确、精度高,能够提供远远超出传统测量技术所能提供的流场信息。DPIV技术作为一种有力的测量手段,在高超声速飞行器研究中能够发挥重大的作用。 相似文献
10.
空化是船舶和水下航行体推进器中经常发生的一种特殊流动现象,它具有强烈的非定常性,空化的发生往往会影响推进器的水动力性能和效率. 为探究绕水翼非定常空化流场结构,本文基于 Schnerr-Sauer 空化模型和 SST $k$-$\omega $ 湍流模型,开展绕二维水翼非定常空化流动数值预报与流场结构分析. 通过将数值预报的空泡形态演变和压力数据与试验结果对比,验证了建立的数值方法的有效性. 并基于动力学模态分解方法对空化流场的速度场进行模态分解,分析了各个模态的流场特征. 结果表明,第一阶模态对应频率为 0,代表平均流场;第二阶模态对应频率约为空泡脱落频率,揭示了空泡在水翼前缘周期性地生长与脱落,第三阶模态对应频率约为第二阶模态的 2 倍,揭示了两个大尺度旋涡在水翼后方存在融合行为. 第四阶模态对应频率约为第二阶模态的 3 倍,具有更高的频率,表征流场中存在一些小尺度旋涡的融合行为. 最后对不同空化数下的空化流场进行了模态分解分析,发现脱落空泡的旋涡结构随着空化数的减小而增大,第二阶模态频率随着空化数的减小而减小. 相似文献
11.
B. W. van Oudheusden F. Scarano N. P. van Hinsberg D. W. Watt 《Experiments in fluids》2005,39(1):86-98
The vortex formation and shedding process in the near wake region of a 2D square-section cylinder at incidence has been investigated by means of particle image velocimetry (PIV). Proper orthogonal decomposition (POD) is used to characterize the coherent large-scale flow unsteadiness that is associated with the wake vortex shedding process. A particular application of the POD analysis is to extract the vortex-shedding phase of individual velocity fields, which were acquired at asynchronous low rate with respect to the vortex shedding cycle. The phase of an individual flow field is determined from its projection on the first pair of POD modes, allowing phase averaging of the measurement data to be performed. In addition, a low-order representation of the flow, constructed from the mean and the first pair of POD modes, is found to be practically equivalent to the phase-averaged results. It is shown that this low-order representation corresponds to the basic Fourier component of the flow field ensemble with respect to the reconstructed phase. The phase-averaged flow representations reveal the dominant flow features of the vortex-shedding process and the effect of the angle of incidence upon it. 相似文献
12.
The effect of the streamwise vortex generators on the near-wake flow structure of a circular cylinder was experimentally investigated.
Digital particle image velocimetry (DPIV) measurements were performed in a large circulating water tunnel facility at a Reynolds
number of 41,300 where the flow around a bare cylinder was expected to be at the sub-critical flow state. In order to capture
various flow properties and to provide a detailed wake flow topology, the DPIV images were analysed with three different but
complementary flow field decomposition techniques which are Reynolds averaging, phase averaging and proper orthogonal decomposition
(POD). The effect of the vortex generators was clearly demonstrated both in qualitative and in quantitative manner. Various
topological features such as vorticity and stress distribution of the flow fields as well as many other key flow characteristics
including the length scales and the Strouhal number were discussed in the study. To the best of the authors’ knowledge, the
study presents the first DPIV visualization of the near-wake flow of a circular cylinder fitted with the vortex generators
in the open literature. 相似文献
13.
In this experimental study, we address transport processes in a mixed convective flow over a heated wavy surface. Therefore,
we combine digital particle image velocimetry (DPIV) and two-color planar laser induced fluorescence (PLIF) to simultaneously
measure the velocity and temperature field. For this, we propose to use the dye combination Rhodamine B and Rhodamine 110,
both excited with the Nd:YAG laser also used for the PIV measurements. We investigate the influence of mixed convection over
a wavy surface on the velocity field, turbulence statistics, the temperature field and the heat flux. By computing these quantities
we find a correlation between the maximum in the Reynolds stress profiles and the components of the heat flux vector, thus
regions of maximum momentum and scalar transport coincide. In addition, we apply a proper orthogonal decomposition (POD) to
extract the most dominant flow structures in a measurement plane above the wavy surface. This first POD mode is identified
as streamwise-oriented, counter-rotating vortices whose spanwise scaling is also correlated with the maximum of heat flux. 相似文献
14.
Planar velocity data of the unsteady separated flow in the turbulent wake of a circular cylinder obtained by particle image
velocimetry (PIV) are analyzed in order to visualize the large-scale coherent structures associated with alternating vortex
shedding at a Reynolds number of 2,150. Two different cases are examined: unforced vortex shedding in the natural wake and
vortex lock-on incited by forced perturbations superimposed in the inflow velocity. Proper orthogonal decomposition (POD)
is employed to reconstruct the low-order wake dynamics from randomly sampled snapshots of the velocity field. The reconstructed
flow is subsequently used to determine the evolution of the finite-time Lyapunov exponent (FTLE) fields which identify the
Lagrangian coherent structures. The results demonstrate that the combination of methods employed offers a powerful visualization
tool to uncover large-scale coherent structures and to exemplify vortex dynamics in natural and forced bluff-body wakes. 相似文献
15.
This paper investigates the flow structure in the wake behind the centrebody of an annular jet using time-resolved stereoscopic
PIV measurements. Although the time-averaged flow field is symmetric, the instantaneous wake is asymmetric. It consists of
a central toroidal vortex (CTV), which closes downstream at the stagnation point. This stagnation point lies off-axis and
hence the axis of the CTV is tilted with respect to the central axis of the geometry. The CTV precesses around the central
axis, corresponding to a Strouhal number of 2.5 × 10−3. The phase averaging technique is used to study this large-scale motion as it can separate the precession from the turbulence
in the flow field. It is found that the precession creates a highly three-dimensional flow field and for instance near the
stagnation point, up to 45% of the rms velocity fluctuations are attributed to it. 相似文献
16.
The ultrasonic velocity profile measurement of flow structure in the near field of a square free jet
Coherent structures in the near field of a three-dimensional jet have been investigated. Experiments were carried out for
a free jet issuing from a square nozzle using a water channel. Instantaneous velocity profiles were obtained in the axial
and radial directions by using an ultrasonic velocity profile (UVP) monitor. Axial variations of dominant time-scales of vortex
structures were examined from one-dimensional wavelet spectra. Wavenumber-frequency spectra were calculated by two-dimensional
Fourier transform along the axial direction in a mixing layer, and it was found that a convective velocity of flow structures
was nearly constant independently of their scales in space and time. Coherent structures in the axial direction were investigated
in terms of proper orthogonal decomposition (POD). Eigenfunctions are similar to a sinusoidal wave, and reconstructed velocity
fields by the lower-order and higher-order POD modes demonstrate large-scale and smaller-scale coherent structures, respectively.
Received: 8 May 2000/Accepted: 23 January 2001 Published online: 29 November 2001 相似文献
17.
S. V. Alekseenko V. A. Antipin A. V. Bobylev D. M. Markovich 《Experiments in fluids》2007,43(2-3):197-207
PIV technique is applied for measurements of instant velocity distributions in a liquid film flowing down an inclined tube
in the form of a wavy rivulet. An application of special optical calibration is applied to correct distortion effects caused
by the curvature of the interface. A vortex flow of liquid is observed inside a wave hump in the reference system moving with
wave phase velocity. Conditionally averaged profiles of longitudinal and transverse components of liquid velocity are obtained
for different cross-sections of developed non-linear waves. It is shown that the increase in wave amplitude slightly changes
the location of the vortex center. The analysis of modification of vortex motion character due to wavy flow conditions, such
as tube inclination angle, film Reynolds number, wave excitation frequency, is fulfilled. 相似文献