Passive control of circular cylinder wake in shallow flow

The control of vortex shedding of a circular cylinder in shallow water using a splitter plate located in the downstream of the circular cylinder was studied by employing particle image velocimetry (PIV) technique. Experiments were carried out in a water channel having a test section of 8000 mm × 1000 mm × 750 mm dimensions at a Reynolds number of 6250. The length of the splitter plate (L) was varied within the range of 0.5 ? L/D ? 2 with an increment of 0.5. The plate was submerged into water at different height ratios (h_p/h_w) such as 0.25, 0.5, 0.75 and 1.0. Mean velocity vector field, corresponding vorticity contours, streamline topologies and turbulent quantities were calculated using 300 instantaneous velocity vector field measured by PIV. As the ratio of h_p/h_w increases, the effect of the splitter plate on the suppression of the vortex shedding increases. Flow characteristics and examination of spectra indicate that Karman vortex shedding is attenuated pronouncedly for the cases of L/D ? 1 and h_p/h_w ? 0.75. The transverse Reynolds normal stress is more effective on the attenuation of turbulent kinetic energy than the streamwise Reynolds normal stress. The value of peak transverse Reynolds normal stress is reduced to 90% of that of the bare cylinder at most.     

Particle image velocimetry study of parameter influence for synthetic-jet application

Flow separation control of a circular cylinder using a synthetic jet positioned at the front stagnation point is experimentally investigated by the particle image velocimetry (PIV) technique. The control results for different excitation parameters, including the stroke length, the excitation frequency, and the momentum coefficient, are compared to distill the essential control parameters, and the influence of the cylinder Reynolds number on the control effect is discussed. The separation control mechanism for the present control configuration is also revealed. It is suggested that the effective control ability of the synthetic jet is attributed to the increment of the turbulent kinetic energy (TKE) and the dissipation rate surrounding the circular cylinder. High level of TKE enhances the dynamics of the fluids and thus flow around the leeward surface is endured a considerable vertical acceleration pointing to the centerline from both sides, which is more resistant to flow separation.     

板翅式换热器封头结构物流分配的PIV实验研究

在数值模拟的基础上,利用粒子图像测速仪(PIV)对板翅式换热器原始封头A和3种改进的顺排孔板型封头结构(B、C、D)的流场进行了可视化的实验,获得了封头内部不同截面处流场的速度流线分布图.比较了Re＝6.22×10⁴时原始封头A和一种改进型封头B的出口物流分配以及3种不同中孔面积比率的改进型封头对出口物流分配的影响.结果表明：改进型封头结构能有效地改善物流分配的均匀性;C型封头的不均匀参数S_U和最大流速与最小流速之比θ_U最低;流量分布和中孔面积比率之间存在着一个最佳值.     

氯化法钛白氧化反应器气体错流混合

氧化反应器是氯化法制取钛白粉的关键设备，混合区的流场设计直接影响反应产品TiO₂颗粒的质量（如粒径和粒径分布）.利用无干扰流场测试技术——粒子图像测速仪（PIV）研究了不同气体错流混合区的结构设计对混合区域流场的影响，考察了气流动量比、射流狭缝宽度以及射流角度对混合区流场的影响.结果表明，较大的气流动量比、窄射流狭缝宽度和接近90°的射流能获得更好的混合区速度分布.进一步利用计算流体力学（CFD）手段对相应的流场进行了模拟，与PIV实验结果吻合很好，验证了模型对冷态流动的预测能力.     

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry(PIV) technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics(CFD) simulations.     

煤液化调节阀湍流特性及稳定性研究

针对湍流流动对煤液化调节阀内部流场稳定性影响,基于粒子图像测速技术(Particle Image Velocimetry, PIV)和能量梯度理论对煤液化调节阀的脉动流场信息进行测量和表征。采用数值模拟和实验相结合的方法,探究了1.2,1.4,1.6,1.8 MPa 4种进口压力条件下(出口压力固定为1 MPa、开度固定为60%)脉动速度均方根、湍流动能等湍流特性参数的变化规律,并结合能量梯度理论对调节阀内流动稳定性展开分析。结果表明,脉动速度均方根的分布与湍流动能的分布具有相似性,高速主流区域位于阀芯头部低速流体的交界处,脉动速度均方根及湍动能值随流速增大而升高,并在轴向位置x为29.73 mm处达到峰值;高速主流与周围低速流体自身剪切产生的速度梯度是造成流场失稳的主要因素;整个流场最不稳定的位置分布在节流口下方阀芯和阀座壁面位置以及高速主流核心区外的剪切层内,进一步揭示了煤液化调节阀失稳机理。     

三相旋流抛光磨粒运动的测量与微气泡补偿

研究了气液固三相旋流流场抛光机理和规律。设计了三入口的抛光加工流道,对气液固三相旋流抛光流场进行了数值模拟。基于模拟结果设计了气液固三相磨粒流旋流流场测量平台,并通过粒子图像测速法(PIV)测量了微气泡补偿条件下气液固三相旋流抛光的流场参数,获得了微气泡补偿区域流场的运动图像、速度矢量图和涡量图。PIV测量试验数据显示:在微气泡补偿区域,磨粒速度主要集中在30m/s到80m/s,同一测量点高速磨粒出现频率明显增加,少数磨粒速度达到100m/s以上;磨粒平均速度从33.8m/s增大到44.2m/s,经4h抛光后硅片表面最大粗糙度从10.4μm下降到1.3μm。理论和试验研究表明,气液固三相旋流抛光流场中微气泡溃灭引发的空化冲击效应可增大磨粒动能,提高抛光效率,实现B区域的均匀化抛光。     

沟槽数量对泰勒涡流稳定性的影响

用粒子图像测速技术(Particle image velocimetry,PIV)对光滑壁面和沟槽数量为18的模型内的流场进行测量,初步获得沟槽的存在对于环隙内流场的影响规律;同时利用数值计算获得沟槽数量为18的模型内的流场分布,通过对比试验结果和数值模拟结果,验证数值计算方法可靠性。通过数值计算研究沟槽数量0、6、12、18模型内的流场分布,在比较沟槽模型与光壁模型环隙内的速度场和涡量场的基础上,得出以下结论：较少的沟槽数量增加了泰勒涡的轴向尺寸,随着沟槽数的增加,沟槽结构对流场影响不断加剧,环隙内最大径向速度和轴向速度均有不同程度的增加;对比不同轴向位置的流场分布,发现沟槽区域内存在明显的旋涡流动,不同轴向位置沟槽内的流体存在着进出环隙内的运动。     

3D Particle image velocimetry test of inner flow in a double blade pump impeller

The double blade pump is widely used in sewage treatment industry,however,the research on the internal flow characteristics of the double blade pump with particle image velocimetry(PIV) technology is very little at present.To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions,inner flows in a double blade pump impeller,whose specific speed is 111,are measured under the five off-design conditions and design condition by using 3D PIV test technology.In order to ensure the accuracy of the 3D PIV test,the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied.The 3D PIV relative velocity synthesis procedure is compiled by using Visual C++ 2005.Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained.Test results show that vortex exists in each condition,but the location,size and velocity of vortex core are different.Average absolute velocity value of impeller outlet increases at first,then decreases,and then increases again with increase of flow rate.Again average relative velocity values under 0.4,0.8,and 1.2 design condition are higher than that under 1.0 design condition,while under 0.6 and 1.4 design condition it is lower.Under low flow rate conditions,radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate,while that of relative velocities at the suction side near the pump shaft decreases.Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions.The research results can be applied to instruct the hydraulic optimization design of double blade pumps.     

Measurement of three-dimensional flame structure by combined laser diagnostics

To investigate three-dimensional flame structures of turbulent premixed flame experimentally, dual-plane planar laser induced fluorescence (PLIF) of CH radical has been developed. This dual-plane CH PLIF system consists of two independent conventional CH PLIF measurement systems and laser beam from each laser system are led to parallel optical pass using the difference of polarization, and CH PLIF is conducted in two parallel two-dimensional cross sections. The newly-developed dual-plane CH PLIF is combined with single-plane OH PLIF and stereoscopic particle image velocimetry (PIV) to clarify the relation between flame geometry and turbulence characteristics. The laser sheets for single-plane OH PLIF and stereoscopic PIV measurement are located at the center of two planes for CH PLIF. The separation between these two planes is selected to 500 μm. The measurement was conducted in relatively high Reynolds number methane-air turbulent jet premixed flame. The experimental results show that various three-dimensional flame structures such as the handgrip structure, which has been shown by three-dimensional direct numerical simulations (DNS), are included in high Reynolds number turbulent premixed flame. It was shown that the simultaneous measurement containing newly-developed dual-plane CH PLIF is useful for investigating the three-dimensional flame structures. To analyze the flame structures quantitatively, the flame curvature was estimated by using the CH and OH PLIF images, and the probability density function (pdf) of the curvatures was compared with the results of DNS. It was revealed that the minimum radius of curvature of the flame front coincides with Kolmogorov length. However, the feature of pdf of the flame curvature is slightly different from result of DNS, if the curvature was estimated from experimental results in two-dimensional cross section. On the other hand, the feature of pdf of mean curvature that calculated from triple-plane PLIF results is similar to that obtained from three-dimensional DNS. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Takashi Ueda received his B.S. degree in Mechano-Aerospace Engineering from Tokyo Institute of Technology, Japan, in 2008. Mr. Ueda is currently in Master course at Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo, Japan. Mr. Ueda’s research interests include turbulent combustion. Masayasu Shimura received his B.S. degree in Mechano-Aerospace Engineering from Tokyo Institute of Technology, Japan, in 2005. He then received his M.S. from Tokyo Institute of Technology in 2006. Mr. Shimura is currently in Ph.D candidate at Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo, Japan. Mr. Shimura’s research interests include noise control of turbulent combustion. Mamoru Tanahashi received his B.S. degree in Mechanical Engineering, Science from Tokyo Institute of Technology, Japan, in 1990. He then received his M.S. and Dr. Eng. from Tokyo Institute of Technology in 1992 and 1996, respectively. Prof. Tanahashi is currently an Associate Professor of Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo, Japan. Prof. Tanahashi’s research interests include turbulence and combustion. Toshio Miyauchi received his B.S. degree in Mechanical Engineering from Tokyo Institute of Technology, Japan, in 1971. He then received his M.S. and Ph.D. degrees from Tokyo Institute of Technology in 1973 and 1981, respectively. Prof. Miyauchi is currently a Professor of Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo, Japan. Prof. Miyauchi’s research interests include turbulence and combustion.