不同材质风力机叶片绕流流场特征变化PIV实验研究

考虑风力机叶片变形对绕流流场的影响,通过粒子图像测速（PIV）方法,采集两副翼型相同、材质分别玻璃聚酯（叶片Ⅰ）和玻璃聚醋内部填充泡沫（叶片Ⅱ）的水平轴风力机叶片绕流流场信息,对不同测试截面处流场数据进行分析。研究结果表明：相比于叶片Ⅰ,相同工况下,叶片Ⅱ的总体涡量、回流区的面积和时均速度更大,轴向雷诺应力更小;随着相对轴向距离的增加,时均速度在相对高度方向波动减小,材质对轴向雷诺应力影响逐渐减弱。实验工况下,叶片材质对绕流流场特征的影响大于叶尖速比对其的影响,并沿径向方向有增大的趋势。     

Velocity Field Structure and Flocculation Efficiency in Taylor-Couette Flow

Velocity field data were acquired for Taylor-Couette flow in the annulus gap between a rotating inner cylinder and a fixed concentric outer cylinder by using particle image velocimetry. The flocculation efficiencies were also obtained in the same Taylor-Couette flow under the conditions corresponding to the velocity field measurement. The flocculation efficiencies reached the maximum values due to the closed vortices, their contraction and expansion with time in wavy vortex flow. But out of the wavy vortex flow range, the comparatively low flocculation efficiencies were obtained due to the no-closed vortices which connected with each other.     

Experimental detection of bubble-wall interactions in a vertical gas-liquid flow

Bubble motions and bubble-wall interactions in stagnant liquid were experimentally investigated by high-speed CCD and PIV technique with the main feature parameters such as E(o)tv(o)s numbers Eo =0.98-1.10,Morton number Mo =3.21 × 10-9 and Reynolds numbers Re =180 ～ 190.The effect of bubble injecting frequency and the distance S between the gas injection nozzle and the wall on the statistical trajectory of bubbles,average velocity distribution of flow field and Reynolds shear stress were studied in detail.It was shown that the combination of bubble injecting frequency and the distance S caused different bubble motion forms and hydrodynamic characteristics.When the normalized initial distance was very little,like S* ≈ 1.2 (here S* =2S/de,and de is the bubble equivalent diameter),bubbles ascended in a zigzag trajectory with alternant structure of high and low speed flow field around the bubbles,and the distribution of positive and negative Reynolds shear stress looked like a blob.With the increase of distance S*,bubbles' trajectory would tend to be smooth and straight from the zigzag curve.Meanwhile,with the increase of bubble injecting frequency,the camber of bubble trajectory at 20 ＜ y ＜ 60 mm had a slight increase due to the inhibitory effect from the vertical wall.Under larger spacing,such as S* ≈ 3.6,the low-frequency bubbles gradually moved away from the vertical plane wall in a straight trajectory and the high-frequency bubbles gradually moved close to the vertical wall in a similar straight trajectory after an unstable camber motion.Under the circumstances,high-speed fluid was mainly distributed in the region between the wall and the bubbles,while the relative large Reynolds shear stress mainly existed in the region far away from the wall.     

PIV measurement on internal instantaneous flows of a centrifugal pump

In this paper,the internal flow field in a centrifugal pump working at the design flow rate operating condition has been measured using the particle image velocimetry(PIV)technique with the fluorescent particles and the index-matched fluid technology.The index-marching fluid with the same refractive index as the transparent material has been prepared and applied in the present test of pump with geometrical complex walls.The comparison between velocity distributions of PIV results both with and without fluor...     

扫描光屏法在PIV技术测量自由剪切层中的应用

ＰＩＶ技术是九十年代实验流体力学的重大成就。它能够提供瞬时整个流场的定量信息，而且具有很高的空间分辨率和很好的精度。为了获得清晰可靠的ＰＩＶ底片，人们对实验方法作了很多改进。本文讨论了近年使用较多的扫描光屏法，提出了该方法在使用中特别注意的一些问题，并给出了用该方法测量自由剪切流场的结果。     

基于MEMS技术的微流体混合器及相关技术

介绍了基于MEMS技术的微流体混合器及相关技术,给出了各种微流体混合器的结构、原理和特点,同时对微管道中流体混合的仿真、实验技术以及微管道中微量流体混合程度的评价方法等作了概述。     

旋转切向流强化管式膜微滤机理研究

首次设计出了旋转切向流管式膜分离器及其实验系统，通过理论研究和实验测试，系统地研究了旋转直线切向流和旋转圆弧切向流聚丙烯管式膜微滤的流场特征，揭示了旋转切向流强化膜微滤的机理。     

Fully Stratified Particle-Laden Flow in Horizontal Circular Pipe

This article describes the results of an experimental measurement and visualization of coarse-grained fully stratified particle-water mixtures. This article focuses on the study of the carrier liquid velocity field and behavior and local velocities of conveyed particles. Glass balls and graded pebble gravel of 6 mm mean diameter were conveyed by water in a horizontal smooth pipe loop with a transparent pipe viewing section of inner diameter 40 mm. The measurements were performed in the smooth pipe and the pipe with rough stationary bed created by two layers of spherical particles of the same mean diameter as the conveyed particles. Particle movement along the pipe bottom was studied and the effect of the stationary bed on local velocity values of the carrier liquid and conveyed particles were evaluated. It was concluded that in the flow with stationary bed the maximum liquid velocity is markedly shifted from the pipe center to its top. The coarse-grained particles moved principally in a layer close to the pipe invert, for higher flow velocities particle saltation becomes the dominant mode of transport.     

旋流燃烧室内等温流场特性的研究

采用三维轴对称RNG k ε湍流模型模拟了微型燃气轮机旋流燃烧室内的等温流场,用粒子测速仪(PIV)测量了旋流燃烧室内不同截面位置的速度矢量分布。对数值模拟结果与实验数据进行了比较分析,研究结果表明:旋流空气在燃烧室头部形成回流区,PIV实验测量的中心回流区范围小于计算结果,燃烧室中心轴的速度小于周围区域的速度,旋流燃烧室内的环向速度衰减较慢,燃烧室内充满旋流。在实验过程中,发现垂直于轴向的横截面PIV测量结果优于轴向截面的PIV测量结果;适当地增加光面厚度,有利于捕捉到更多的粒子,提高测量精度。图6参7。     

Simultaneous visualization of flow field and evaluation of local heat transfer by transitional impinging jets

A combined approach has been employed to characterize the flow field and local heat transfer in jet impingement configurations, featuring a mass transfer experiment and a digital visualization technique. A jet velocity range is spanned to ensure flow regime transition.The well-known heat/mass transfer analogy has been used to infer on the local heat exchange on a infinite plate. In this experiment, a naphthalene film is ablated from a disk, due to jet exposure. Automated contact measurements of the variation of film depth in the stagnation region and beyond have been performed. From the local naphthalene loss rate the local heat transfer is then inferred. Coherent structures are created both at the interface between free jet and quiescent medium and upon impingement at plate, and need to be visualized in the vicinity of stagnation. To this end a particle image velocimetry system is exploited to extract the two components velocity instantaneous information.Ablation measurements confirm the non-monotonic progress of local heat transfer for small nozzle-to-plate spacings. The visualizations evidence that local heat transfer is strongly influenced by impingement structures: the maximum heat transfer coefficient offset which can be detected is due, even for laminar or transitional jet, to large-scale toroidal vortices impacting on the plate.