PIV MEASUREMENT OF THE GAS-SOLID FLOW PATTERN IN A CFB RISER

Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studying multiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out many hydrodynamic studies, in particular, to determine accurately the gas-solid flow structure in CFB (Circulating Fluidized Beds). In this paper, the technique characteristics was described in applying the PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment was completed on a CFB unit with the PIV, yielding the velocity vector fields of high-density particles for different gas-solid superficial velocities and solid recycle rates. Velocities of the transported particles were calculated with cross-correlation method. The major factors influencing the successful measurement of particle velocity with the PIV technique were also described.     

循环流化床环核结构速度分布PIV测试

利用粒子图像测速仪（PIV）对循环流化床中颗粒流场进行了系统的实验研究。运用适合于高粒子浓度的最小方差法（MQD）图像处理算法得到了截面内典型环核流动颗粒速度矢量场。采用速度矢量场的方法可以确定出环核结构分界。定量上获得了不同时刻颗粒轴向上升和下落平均速度大小及沿床径向分布特性。在统计颗粒轴向上升速度和下落速度代数和基础上,获得了总体上颗粒轴向速度沿床径向在整个截面内形成抛物线型的环核分布规律。     

PIV技术在冰盖下复式断面渠道流速测量中的运用

在测定冰盖下复式断面流场、流速的模型试验中,水体中的运动粒子是重点研究对象。粒子图像测速(Particle Image Velocimetry,PIV)技术已在水力学研究领域得到普遍应用,但该技术在冰盖下复式断面渠道模型试验的应用为国内首次。基于试验特点,设计砖砌混凝土的循环水箱,采用变频器配合水泵、流量计实现对流量的定量控制,对不同流量下不同断面的流场、流速进行测定,采用PIV技术对水体中运动的粒子的位移场进行具体分析。试验结果表明,PIV分析结果能够直观反映流场中的状态,且可以避免测量盲区,其所测的流速与多普勒超声测速仪测得值吻合较好,并给出了横向流速分布图,弥补了传统方法无法获得冰盖下的流场分布的难题。     

导叶开度对水泵水轮机泵工况导叶区流场影响的试验研究

针对活动导叶开度对水泵水轮机泵工况导叶区流场和模型性能的影响,在高精度模型通用试验台上对一低比转速模型水泵水轮机导叶区的流场运用粒子图像测速(PIV)系统进行了测量。测量结果显示,同一开度下随着流量减小,无叶区内的流速出现增大的趋势;同一流量随着开度的减小,导叶前流速明显增大,模型效率下降。模型试验在转轮无空化条件下进行,但在8 mm开度83%最优流量工况,由于流速高、冲角大,造成位于高压侧的导叶头部发生了明显的绕流空化现象,并引起了固定导叶流道宽频带的压力脉动。研究成果可为水泵水轮机的优化设计和安全稳定运行提供试验依据。     

RESEARCH OF INNER FLOW IN A DOUBLE BLADES PUMP BASED ON OPENFOAM

The inner flow analysis of centrifugal pumps has gradually become an important issue for the hydraulic design and performance improvement.Nowadays,CFD simulation toolbox of pump inner flow mainly contains commercial tools and open source tools.There are some defects for commercial CFD software for the numerical simulation of 3-D turbulent internal flow in pump,especially in capturing the flow characteristics under the off-design operating conditions.Additionally,it is difficult for researchers to do further investigation because of the undeclared source.Therefore,an open source software like Open Field Operation and Manipulation (OpenFOAM) is increasingly popular with researchers from all over the world.In this paper,a new computational study was implemented based on the original solver and was used to directly simulate the steady-state inner flow in a double blades pump,with the specific speed is 111.In order to disclose the characteristics deeply,three research schemes were conducted.The ratios () of the flow rate are 0.8,1.0 and 1.2,respectively.The simulation results were verified with the Particle Imaging Velocimetry (PIV) experimental results,and the numerical calculation results agree well with the experimental data.Meanwhile,the phenomena of flow separation under the off-design operating conditions are well captured by OpenFOAM.The results indicate that OpenFOAM possesses obvious strong predominance in computing the internal flow field of pump.The analysis results can also be used as the basis for the further research and the improvement of centrifugal pump.     

PIV MEASUREMENTS OF THE NEAR-WAKE FLOW OF AN AIRFOIL ABOVE A FREE SURFACE

The near-wake flow of a NACA0012 airfoils mounted above a water surface were experimentally studied in a wind/wave tunnel. The main objective of this study is to investigate the influence of the free surface on the structure of the airfoil trailing wake. The flow structure was measured with different ride heights between the airfoil and free surface using a Particle Image Velocimetry (PIV) system. The Reynolds number based on the chord length of the airfoil was about 3.5×103. For each experimental condition, large amount of instantaneous velocity fields were captured and ensemble-averaged to get the spatial distributions of mean velocity and mean vorticity, as well as turbulence statistics. The results show that the flow structures of the airfoil wake varies remarkably with the change in the ride height.     

The flow patterns of bubble plume in an MBBR

The flow patterns of the gas-liquid two-phase flow in a Moving-Bed Biofilm Reactor (MBBR) have a critical effect upon the mass transfer by the convection.Bubble plumes promote unsteadily fluctuating two-phase flows during the aeration.This article studies the unsteady structure of bubble plumes through experiments.The time-serial bubble plume images in various cases of the tank are analyzed.The Recursive Cross Correlation-Particle Image Velocimetry (RCC-PIV) is used to calculate the velocities in those cases, and then the time-serial vortex, the total turbulence intensity, the time-serial streamline are obtained.It is shown that the aspect ratio and the void fraction are the dominant factors influencing the unsteady structure of bubble plumes.When the aspect ratio is unity and the void fraction is high, the bubble plumes see a symmetrical vortex structure with a long residence time, which is beneficial for optimizing the aeration system and enhancing the applied range of bubble plumes.