混流式转轮出口流速分布的PIV测试研究

转轮出口速度分布好坏直接影响尾水管内压力脉动的大小,是影响稳定性的内在因素之一。本文针对HL220改型的模型试验,对转轮出口的速度内流分布,采用2D-PIV激光内流速测试设备对锥管内径向面进行了内流测试,给出了最优工况下转轮出口处径向面的流动瞬态分布,清楚显示了尾水管进口位置在最优工况下的流动非定常特征与细节。试验结果表明,PIV内流测试是进行转轮出口流动测量的一种可靠方法,结果为研究尾水管内的流动分布提供了必要的依据和边界条件。     

大型淋雨设备管内流动的CFD模拟与分析

应用计算流体动力学方法(CFD)对某大型淋雨试验设备竖直淋雨管内的水流场进行了计算机模拟,从而获得管内及各喷嘴内流场压力、速度和流量的分布特点,并重点对比分析了在中间进水、底端进水、顶端进水和两端同时进水4种情况下各喷嘴流量的一致性,为确定合理的进水位置方案从而保证均匀淋雨提供参考。     

基于PIV测量技术的变曝气量下气液两相流速度场研究

粒子图像测速技术(PIV)作为一种无扰的全流场速度测量手段,在多相流研究领域具有较高的学术意义和实用价值。本研究针对曝气过程中的复杂气液两相流动,使用高速摄影机获取气液两相流流场的高帧图像,再通过图像预处理手段及PIV测速算法得到气液两相流速度场信息,并对不同工况下气液两相流的流态流速规律进行了研究分析。本文提出的图像预处理方案,通过采用图像的运动目标分割、降噪与反相等手段进行图像预处理,可以有效地减少后续速度场计算中的信息量及误差。研究结果为工业生产过程中有效提高曝气效率提供了重要的参考依据。     

应用激光多普勒效应测量浑水流速的实验研究

黄河是举世闻名的多沙河流,对于泥沙运动规律的研究是治黄工作中一项极为重要的课题.激光多普勒效应(即LDV技术)能不能用于浑水测量流速,1980年9月和1982年利用本所研制的测速装置做了浑水流速的静态和动态探索性实验研究工作.本文对激光在浑水中传输特性和相干条纹的视见度以及实验结果进行简要分析.     

采用乳化空气泡做示踪粒子的PIV测速技术

本文介绍一种适用于水洞力学实验的采用乳化空气泡作为示踪粒子的ＰＩＶ测速技术。选用乳化空气泡做ＰＩＶ测速示踪粒子，取代了通常采用的固体颗粒，由两台ＹＡＧ大功率脉冲式激光光源组合系统做为ＰＩＶ底片记录的双脉冲曝光光源。乳化空气泡的最大优点是对实验水洞或水槽无污染，且产生方便、经济，又可以形成高质量的杨氏条纹图像。这一技术能够使得ＰＩＶ测速技术在水洞力学应用测量中真正达到实用。     

轴流式水轮机导流罩与叶轮尾流流场仿真研究

文中提出一种新型轴流、悬浮式潮流能水轮机结构,为提高其潮流能利用效率,采用CFD技术对水轮机外围流线型导流罩内流场与叶轮尾流场进行数值仿真研究。通过对比拟定的10种不同线型导流罩,发现收缩段和扩散段的进出口曲线前后连接点比例mx为0.3的双三次曲线导流罩内流场更加稳定、均匀。为进一步研究导流罩的聚能作用与叶轮尾流场的速度分布情况,实施了有、无导流罩工况下水轮机的数值仿真,结果显示:距离叶轮下游边缘1.25D(D为叶片直径)以内的流场域流速有显著的改变,且加装双三次曲线0.3mx=线型导流罩,水轮机较敞水工况输出功率提高约29%。相关的拖曳水池模型试验验证了数值仿真方法的有效性。     

水下高速喷气气水流场研究

水下喷气是一个复杂的过程，本文在一定假设的基础上，将复杂的流场分为三部分：喷管内流场、气泡流场及流体水流场。喷管内流场采用准一维模型，用差分格式求解，气泡模型采用滞止等压泡模型；液体流场采用MAC方法，通过步进法实现三个流场的耦合求解。给出了几种环境压力及速度下的数值计算结果，初步掌握了水下喷气的特征。     

简易粒子图像测速(PIV)技术开发与优化技巧

粒子图像测速(PIV)技术是一种瞬态流动平面二维速度场测试技术,在细部流场实测领域得到重视,但是成熟的PIV产品价格高昂。鉴于此,介绍了一种简易的PIV装置,主要由高速摄像机、激光发射器、柱面透镜和示踪粒子构成,以较低成本即可基本实现商业用PIV产品的功能。为了验证简易PIV性能,设计了PIV简易装置,采用Fluent软件模拟,并结合PIV技术对比分析了简易PIV装置的优缺点,同时对影响结果的粒径大小和粒子跟随性进行了优化。结果表明,简易PIV装置适宜选用玉米粉作为示踪粒子,并需要根据示踪粒子跟随性所能达到的最大进口水流速度选择高速摄像机的帧率,最终能够较好地实现流场实测,进而达到对PIV技术进行开发和优化的目的,其分析结果将为后续研究者提供参考。     

出口边界条件对脑前交通动脉瘤内血流特征的影响

脑前交通动脉是动脉瘤高发且易破裂的区域,其所处的多血管交汇位置使瘤内流场易受周边血流环境的影响。该文以理想化的动脉瘤模型为研究对象,采用CFD方法开展数值实验,考察了模型出口边界条件对瘤内血流参数的影响。结果表明,瘤内流场的结构特征、壁面剪切力等均随模型子管间流量分配比的改变而变化,同时,各参数的受影响程度与所处位置有关。虽然单一模型分析限制了该文研究结论的统计学意义,但研究结果明确了瘤内流场对边界条件的敏感性,提示在脑前交通动脉瘤的血流分析和风险评估中充分考虑脑动脉网络结构及系统血流环境的必要性。     

泗阳泵站出水流道可行性方案对比分析研究

结合泗阳泵站已有土建结构,采用雷诺平均纳维-斯托克斯方程(RANS)和标准k-ε湍流模型,运用SIMPLEC算法,设计虹吸式出水流道、直管式出水流道及钟形出水流道3种可行性方案.分别在流道进口未设置环量和设置环量的情况下,数值模拟3种流道内流场,预测流道内的不良流态形式及出现位置,分析各方案流道进口断面、中间断面及出口...     

THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on theconical swirling water jet flow.Based upon the theoretical analysis,the experiment on thestructural characteristics of swirling water jet flow including the velocity and pressure dis-tribution laws,on which the parameters of the jet,nozzle and directional blades havemore or less influence,was carried out in CSSRC by using a 3-D LDV in order to optimizea new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuouslydrilling,and to meet the demand of radial horizontal drilling technology.Meanwhile basedon the experimental results,the numerical simulation was conducted for the conicalswirling water jet in the immersed well-bottom flow by solving the RANS equations in the3-D body-fitted coordinate system with the k-ε turbulence model.The numerical resultsare consistent with the experimental data,and lead to some conclusions which are impor-tant for applying the conical swirling water jet to the petroleum drill     

水轮机主轴中心孔补气对尾水管内部流态的影响

基于水气两相流模型，研究了水轮机主轴中心孔补气对尾水管涡带的影响以及对于改善水轮机内部流态的作用。研究表明，不同工况下最优补气量的大小有一定的差异；由于气体能量较小，补气量过小，在转轮的影响下它很快稀释于水体中，进入尾水管直锥段中心涡带区域的气体很少，起不到改善水流的作用，补气量过大，又会使断面过水面积减小，尾水管直锥段横向水流增强导致不利流态。研究成果揭示了补气量的大小对于改善尾水管内部水流的影响，从而为寻找最优的补气量提供理论依据。     

Experimental study of shell side flow-induced vibration of conical spiral tube bundle

Conical spiral tube bundles are widely used in enhancing the heat transfer via the flow-induced vibration in heat exchangers. The shell side flow-induced vibration of the conical spiral tube bundle is ...     

Experimental study by PIV of swirling flow induced by trapezoid-winglets

The characteristics of the longitudinal vortex induced by trapezoid-winglets in a circular tube are investigated by the Particle Image Velocimetry （PIV） Technique with flow Reynolds number in the range of 500-13 000. In the experimental test section, four trapezoid-winglets are fixed symmetrically on the tube wall in two different ways： up-flow and down-flow. The results show that a counter-rotating vortex pair is formed behind each winglet and they distribute as a symmetrical vortex array in the transverse section. Between the two vortexes in a vortex pair the fluid flows towards the wall in the up-flow winglet case and away from the wall in the down-flow winglet case, corresponding also to the regions of peak values of the velocity components normal to the mainstream. Both of the flow patterns enhance the velocity in the near wall region, leading to the intensification of the transverse mixing and the mass transfer in the tube. With Reynolds number increasing, the flow maintains the vortex pattern in the case of the up-flow winglets, indicating better persistence of the longitudinal vortex, while the vortexes in the case of the down-flow winglets are more scattered and tend to breaking into small eddies. The trapezoid winglet shows the preferable turbulent disturbance characteristics in the tube and the experimental results provide benchmark data for further CFD studies.     

不同进流浓度梭锥管水沙两相流场三维数值模拟

为了获得全面详细的梭锥管内部流动特性,本文探讨进流浓度对梭锥管内水沙分离效果的影响,据此来揭示梭锥管水力分离水沙的机理。本文采用重整化RNG(renormalization group)紊流模型与简化的多相流Mixture模型在泥沙浓度为5和15 kg/m3时对梭锥管内水沙两相流场进行了三维的数值模拟计算。并将计算结果与PIV测量结果进行对比,计算结果与PIV测试结果一致。结果表明:在进流量相同时随着进流浓度的增加,在上锥管边壁清水上升通道内速度增加,水流挟沙力增强,随水流溢出的泥沙量增多,并且随着进流浓度的增加梭锥管各个断面泥沙体积浓度及紊动强度值也随之增加,上锥管得到的清水面积也随之减小,不利于梭锥管内水沙分离。     

Experimental measurement of tip vortex flow field with/without cavitation in an elliptic hydrofoil

In this paper, recent measurements of tip vortex flow with and without cavitation carried out in Cavitation Mechanism Tunnel of China Ship Scientific Research Center(CSSRC) are presented. The elliptic hydrofoil with section NACA 662-415 was adopted as test model. High-speed video(HSV) camera was used to visualize the trajectory of tip vortex core and the form of tip vortex cavitation(TVC) in different cavitation situations. Laser Doppler velocimetry(LDV) was employed to measure the tip vortex flow field in some typical sections along the vortex trajectory with the case of cavitation free. Stereo particle image velocimetry(SPIV) system was used to measure the velocity and vorticity distributions with and without cavitation. Series measurement results such as velocity and vorticity distributions, the trajectory of tip vortex core, the vortex core radius, cavity size and cavitation inception number were obtained. The results demonstrated that the minimum pressure coefficient in the vortex core obtained by flow field measurement was quite coincident with the tip vortex cavitation inception number obtained under the condition of high incoming velocity and low air content. And TVC would decrease the vortex strength comparing with the case without cavitation.     

AN INVESTIGATION OF FLOW CHARACTERISTIC OF AERATED DRAG REDUCTION IN TUBE

Under the aerated conditions of wall and top intube, the turbulent flow in the tube was measured by usingLDA. The turbulent structure of the flow field and the mech-anism of aerating drag reduction in the tube were discussed. It is shown that the energy dissipations of turbulence flow andmean flow will reduce and the flow velocity (or flow rate) willincrease by injecting mini-bubbles to the wall or top of tube,namely the effect of aerating drag reduction is attained.     

THEORETICAL AND EXPERIMENTAL STUDIES OF HYDRAULIC CHARACTERISTICS OF DISCHARGE TUNNEL WITH VORTEX DROP

The velocities at given points in the volute chamber,the contracted section and the vertical dropshaft of a discharge tunnel with vortex drop were measured by a small specially designed L-shaped tube,as Laser Doppler Velocimetry(LDV) or Particle Image Velocimetry(PIV) would not work there due to the special structure of the discharge tunnel with vortex drop.Hydraulic empirical formulas were proposed to predict the velocities and the angles of the velocities made with the vertical direction θ.The theoretical analysis results were in good agreement with experimental data.Therefore,the method proposed in this paper can be used to analyze related characteristics of discharge tunnels with vortex drop.Additionally,different model scales were considered to predict the cavitation characteristics on the wall of a dropshaft in practical engineering.     

模型溢流反弧的激光测速与紊流过渡区的边界层特性

本文利用激光测速仪对３种不同粗糙度，２种反弧半径的溢流反弧段的水流流速进行了测量，对边界层特性进行了分析研究．试验分析认为，水流流态，壁面粗糙度和壁面曲率对边界层特性有明显的影响     

壁面处湍流状况测试研究

讨论并采用电化学方法，测试矩形管壁面处速度梯度及湍流强度，分析并实验探讨了离子迁移方向对测试电极动态响应的影响，将测试结果与同样条件下激光测速仪在近壁处温度结果进行了分析比较，与其他在圆管流动测试中得出的结论不同，测试结果表明，矩形管壁面外流体相对湍动强度随流量增大而减小，在高雷诺数下趋近常数。