ON ANALYSIS OF THE STEADY FLOW IN AN IRRECTANGULARPARALLEL-PLATE FLOW CHAMBER

The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom of PPFC undergoing shear stress. The PPFC of which the upper and lower plates are rectangular is usually used by research workers, and the flow field in this kind of PPFC (except for the regions near the entrance and exit) is uniform([1]), so only the effect the shear stress with one value has on cultured cells can be observed during each experiment. A kind of PPFC of which the upper and lower plates are not rectangular is proposed in this paper. The distributions of the velocities inside and the shear stresses at the bottom of the chamber are given by analyzing the flow field of the steady flow in the PPFC. The results show that the mechanical behaviors of cultured cells undergoing the shear stresses with various values may be simultaneously observed by the use of this kind of irrectangular PPFC. The theoretical and experimental results obtained by Ultrasonic Doppler Technique show good agreement.

Orthogonal optimization of flow uniformity at exit section of elbow-inlet passages

Elbow-inlet passage is widely used in large drainage pumping stations.Flow uniformity at the exit section directly determines its hydraulic performance.Flow uniformity must be optimized to improve the operational efficiency of the large axial-flow pumping station.Modeling and numerical simulation methods were used to investigate the elbow-inlet passage,and the accuracy of the calculation results was verified.The key geometric parameters affecting the uniformity of the flow were optimized by the orthogonal experiment design.The optimal schemes were obtained and compared with the original scheme.The results show that flow uniformity V u after optimization is 95.41%,which is increased by 1.04%.The pumping station efficiency is increased by 1.89%,thereby confirming the applicability and accuracy of the proposed scheme,especially for the optimization of flow uniformity of the exit section of the elbow-inlet passage.

Effects of Meridional Flow Passage Shape on Hydraulic Performance of Mixed-flow Pump Impellers

During the process of designing the mixed-flow pump impeller, the meridional flow passage shape directly affects the obtained meridional flow field, which then has an influence on the three-dimensional impeller shape. However, the meridional flow passage shape is too complicated to be described by a simple formula for now. Therefore, reasonable parameter selection for the meridional flow passage is essential to the investigation. In order to explore the effects of the meridional flow passage shape on the impeller design and the hydraulic performance of the mixed-flow pump, the hub and shroud radius ratio (HSRR) of impeller and the outlet diffusion angle (ODA) of outlet zone are selected as the meridional flow passage parameters. 25 mixed-flow pump impellers, with specific speed of 496 under the design condition, are designed with various parameter combinations. Among these impellers, one with HSRR of 1.94 and ODA of 90° is selected to carry out the model test and the obtained experimental results are used to verify accuracies of the head and the hydraulic efficiency predicted by numerical simulation. Based on SIMPLE algorithm and standard k-ε two-equation turbulence model, the three-dimensional steady incompressible Reynolds averaged Navier-Stokes equations are solved and the effects of different parameters on hydraulic performance of mixed-flow pump impellers are analyzed. The analysis results demonstrate that there are optimal values of HSRR and ODA available, so the hydraulic performance and the internal flow of mixed-flow pumps can be improved by selecting appropriate values for the meridional flow passage parameters. The research on these two parameters, HSRR and ODA, has further illustrated influences of the meridional flow passage shape on the hydraulic performance of the mixed-flow pump, and is beneficial to improving the design of the mixed-flow pump impeller.

Experimental Study of the Influence of Flow Passage Subtle Variation on Mixed-flow Pump Performance

In the mixed-flow pump design, the shape of the flow passage can directly affect the flow capacity and the internal flow, thus influencing hydraulic performance, cavitation performance and operation stability of the mixed-flow pump. However, there is currently a lack of experimental research on the influence mechanism. Therefore, in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance, the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment. In this experiment, parameters, such as the head, the efficiency, and the shaft power, are measured, and the pressure fluctuation and the noise signal are also collected. The research results suggest that after processing the inlet flow passage, the head of the mixed-flow pump significantly goes down; the best efficiency of the mixed-flow pump drops by approximately 1.5%, the efficiency decreases more significantly under the large flow rate; the shaft power slightly increases under the large flow rate, slightly decreases under the small flow rate. In addition, the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump. At the same time, the noise dramatically increases. Overall speaking, the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance, thus suggesting a special attention to the optimization of flow passage. This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment, which will benefit the optimal design of the flow passage of the mixed-flow pump.

Flow measurement and parameter optimization of right-angled flow passage in hydraulic manifold block

This study was conducted to investigate the flow field characteristics of right-angled flow passage with various cavities in the typical hydraulic manifold block.A low-speed visualization test rig was developed and the flow field of the right-angled flow passage with different cavity structures was measured using 2D-PIV technique.Numerical model was established to simulate the three-dimensional flow field.Seven eddy viscosity turbulence models were investigated in predicting the flow field by comparing against the particle image relocimetry(PIV)measurement results.By defining the weight error function K,the S-A model was selected as the appropriate turbulence model.Then,a three-factor,three-level response surface numerical test was conducted to investigate the influence of flow passage connection type,cavity diameter and cavity length-diameter ratio on pressure loss.The results show that the Box-Benhnken Design(BBD)model can predict the total pressure loss accurately.The optimal factor level appeared in flow passage connection type II,14.64 mm diameter and 67.53%cavity length-diameter ratio.The total pressure loss decreased by 11.15%relative to the worst factor level,and total pressure loss can be reduced by 64.75%when using an arc transition right-angled flow passage,which indicates a new direction for the optimization design of flow passage in hydraulic manifold blocks.

HYDRAULIC CALCULATION AND MEASUREMENT OF FLOW FIELD WITHIN INLET PASSAGE OF LARGE PUMPING STATION

By means of the analysis of the internal flow within inlet passage of large pumping sta-tion, an analysis of 3-D direct boundary element for the flow has been presented on the potentialflow assumption, and a calculation and an experimental proof for the inlet passage of 30 angle-type axial pumping station have been made. Based on the analysis of the calculations and theexperiments, the calculation method is feasible and believable.

Improved Soft Abrasive Flow Finishing Method Based on Turbulent Kinetic Energy Enhancing

Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic energy enhancing is proposed. A constrained flow passage with serration cross-section is constructed to increase the turbulence intensity. Taking the constrained flow passage as the objective, a two-phase fluid dynamic model is set up by using particle trajectory model and standard k-ε turbulence model, and the flow field characteristics of the flow passage are acquired. The numerical results show that the serration flow passage can enhance the turbulence intensity, uniform the particles distribution, and increase the particle concentration near the bottom wall. The observation results by particle image velocimetry（PIV） show that the internal vortex structures are formed in flow passage, and the abrasive flow takes on turbulence concentrating phenomenon in near-wall region. The finishing experiments prove that the proposed method can obtain better surface uniformity, and the processing efficiency can be improved more 35%. This research provides an abrasive flow modeling method to reveal the particle motion regulars, and canoffer references to the technical optimization of fluid-based precision processing.

Numerical simulation and analysis of solid-liquid two-phase threedimensional unsteady flow in centrifugal slurry pump

Based on RNG k-ε turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional(3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of unsteady flow characteristics on solid-liquid two-phase flow and pump performance were researched under design condition. The results show that clocking effect has a significant influence on the flow in pump, and the fluctuation of flow velocity and pressure is obvious, particularly near the volute tongue, at the position of small sections of volute and within diffuser. Clocking effect has a more influence on liquid-phase than on solid-phase, and the wake-jet structure of relative velocity of solid-phase is less obvious than liquid-phase near the volute tongue and the impeller passage outlet. The fluctuation of relative velocity of solid-phase flow is 7.6% smaller than liquid-phase flow at the impeller outlet on circular path. Head and radial forces of the impeller are 8.1% and 85.7% of fluctuation, respectively. The results provide a theoretical basis for further research for turbulence, improving efficient, reducing the hydraulic losses and wear. Finally, field tests were carried out to verify the operation and wear of slurry pump.

Design and Numerical Simulation on Coupled Flow Field of Radial Turbine with Air-Inlet Volute

As one of the core components of turbocharger or micro-turbine, radial turbine has the features of small size and high rotation speed. In order to explore the design method and flow mechanism of the turbine with a volute, a centimeter-scale radial turbine with a vaneless air-inlet volute was designed and simulated numerically to investigate the characteristics of the coupled flow field. The results show that the wheel efficiency of single passage computation without the volute is 80.1%. After accounting for the factors of the loss caused by the volute and the interaction between each passage, the performance is more accurate according to the whole flow passage computation with the volute. High load region gathers at the mid-span and the efficiency declines to 76.6%. The performance of the volute whose structure angle of the trapezoid section is equal to 70 degree is better. Unlike uniform inlet condition in single passage, more appropriate inlet flow for the impeller is provided by the rectification effect of the volute in full passage calculation. Flow parameters are distributed more evenly along the blade span and are generally consistent between each passage at the outlet of the turbine.

In uence of Endwall Boundary Layer Suction on the Flow Fields of a Critically Loaded Di usion Cascade

Boundary layer suction is an e ective method used to delay separations in axial compressors. Most studies on bound?ary layer suction have focused on improving the performance of compressors,whereas few studies investigated the influence on details of the flow fields,especially vortexes in compressors. CFD method is validated with experi?mental data firstly. Three single?slot and one double?slot endwall boundary layer suction schemes are designed and investigated. In addition to the investigation of aerodynamic performance of the cascades with and without suction,variations in corner open separation,passage vortex,and concentration shedding vortex,which are rarely seen for the flow controlled blades in published literatures,are analyzed. Then,flow models,which are the ultimate aim,of both baseline and aspirated cascades are established. Results show that single?slot endwall suction scheme adjacent to the suction surface can e ectively remove the corner open separation. With suction mass flow rate of 0.85%,the overall loss coe cient and endwall loss coe cient of the cascade are reduced by 25.2% and 48.6%,respectively. Besides,this scheme increases the static pressure rise coe cient of the cascade by 3.2% and the flow turning angle of up to 3.3° at 90% span. The concentration shedding vortex decreases,whereas the passage vortex increases. For single?slot suction schemes near the middle pitchwise of the passage,the concentration shedding vortex increases and the passage vortex is divided into two smaller passage vortexes,which converge into a single?passage vortex near the trailing edge section of the cascade. For the double?slot suction scheme,triple?passage vortexes are presented in the blade passage. Some new vortex structures are discovered,and the novel flow models of aspirated compressor cascade are proposed,which are important to improve the design of multi?stage aspirated compressors.

Functional Neuroanatomy of Time-To-Passage Perception

The time until an approaching object passes the observer is referred to as time-to-passage (TTP). Accurate judgment of TTP is critical for visually guided navigation, such as when walking, riding a bicycle, or driving a car. Previous research has shown that observers are able to make TTP judgments in the absence of information about local retinal object expansion. In this paper we combine psychophysics and functional MRI (fMRI) to investigate the neural substrate of TTP processing. In a previous psychophysical study, we demonstrated that when local retinal expansion cues are not available, observers take advantage of multiple sources of information to judge TTP, such as optic flow and object retinal velocities, and integrate these cues through a flexible and economic strategy. To induce strategy changes, we introduced trials with motion but without coherent optic flow (0% coherence of the background), and trials with coherent, but noisy, optic flow (75% coherence of the background). In a functional magnetic resonance imaging (fMRI) study we found that coherent optic flow cues resulted in better behavioral performance as well as higher and broader cortical activations across the visual motion processing pathway. Blood oxygen-level-dependent (BOLD) signal changes showed significant involvement of optic flow processing in the precentral sulcus (PreCS), postcentral sulcus (PostCS) and middle temporal gyrus (MTG) across all conditions. Not only highly activated during motion processing, bilateral hMT areas also showed a complex pattern in TTP judgment processing, which reflected a flexible TTP response strategy.

地下泵站进水流道数值模拟与方案优化

以典型地下泵站的进水流道为研究对象,建立数值仿真模型,分析设计方案的水力特性及存在不足,并给出优化方案.研究结果表明:在原方案中,外侧水泵进水管入口中心和圆洞出口中心的连线与来流方向的夹角达到70°,水流大角度偏转,并在进水管入口出现脱流现象,水头损失系数达到2.31~2.44,水泵进水管出口的流速分布均匀度为95.09%~96.80%,速度加权平均角为86.51°~87.41°,原方案的圆洞突扩进入压力罐,然后突缩进入水泵的进水管,且压力罐内无任何导流措施,致使局部流道产生了较大的水头损失;优化方案提出了“集管+岔管”的分流措施,通过2个60°弯头实现水流流向的偏移,平面和垂直方向均没有突扩或突缩结构,水头损失系数减小至0.93~1.07,优化方案不仅改善了流道的水力性能,也避免了开挖、衬砌压力罐.研究结果可为类似地下泵站进水流道设计提供一定依据.

双吸泵静腔室数值优化与试验分析

【目标】探究影响双吸离心泵效率的主要因素及关键参数,优化设计吸水室以提高水力性能。【方法】基于水力损失最小原则,对吸水室与蜗壳内部流道形状进行设计,研究过流断面面积演变规律。采用CFD数值计算方法对优化前后的泵内流特征及性能特性进行对比分析,并利用实体模型试验验证优化方案的实际性能。【结果】改良设计的工况点效率比原型设计提升3.36%;在0.7QBEP(设计工况)至1.2QBEP范围内,整泵效率相较改进前模型均有所提高。其中,蜗壳水力损失降低明显,除1.3 QBEP损失下降6.18%以外,其余工况下蜗壳水力损失降低幅度均超过20%。对于吸水室,大于0.98 QBEP流量工况时,改进后模型吸水室损失低于改进前模型。【结论】吸水室、蜗壳内部流道的优化设计,明显改善了吸水室内部的不稳定流动,消除了叶轮出口附近的流动旋涡,显著降低水力损失,有效提升双吸泵的水力效率。

进出口流道对轴流泵性能影响的数值模拟分析

冷却剂流态是影响核主泵装置工作性能的重要因素,而进出水流道的结构影响着进出水流态。在保证叶轮和导叶结构不变的情况下,探究不同的进出口流道结构对泵水力性能的影响。本文基于SST k-ω湍流模型和SIMPLEC算法,使用三个常用的商业计算流体力学软件对采用不同入口弯管、蜗壳和出口直管的轴流泵进行网格无关性分析和全流域稳态数值计算。经计算,两个模型的外特性参数一致,流量特性曲线几乎重合,且轴流泵的进出水流态相似。不同商业流体力学计算软件得到的曲线和云图的趋势一致,各软件计算误差均在5%以内,证明本次研究中进出口结构改型对泵的水力性能没有产生明显的影响。

不同偏角变径流道质子交换膜燃料电池性能仿真分析

为了研究变径区域的不同偏角下质子交换膜燃料电池(PEMFC)的性能,基于ANSYS Fluent软件对不同偏角下的电池流道中气体流速、质量分数、压强以及水含量进行了仿真模拟,分析结果表明:在不同偏角下流道流速主要在6~7 m/s之间,流速点占比相对较大对应的偏角为50°,相对较小的对应偏角为75°;相对较大流速对应的偏角为75°和60°,随着偏角的增加,阳极氢气绝对压强曲线线性增加速率相对较大的对应偏角为70°和75°,相对较小的对应的偏角为40°;阴极氧气绝对压强曲线相对较大的对应的偏角为60°,相对较小的对应的偏角为40°;在出口处流道水质量分数相对较大的对应偏角为40°、70°和75°,而相对较小的对应角度为60°。综合考虑分析可以得出,电池效率相对较好的适宜偏角为60°。

渗流地层地铁联络通道冻结壁形成过程及其影响因素分析

冻结法凭借封水性好、适应性强和环境影响小等优势成为地铁联络通道施工的主要工法之一,而地下水渗流易引起冻结壁交圈时间延后、厚度和平均温度不及预期,对冻结工程的推进具有不利影响。本文采用频域反射法获取饱和砂砾石未冻水体积分数和温度的函数关系式,基于多孔介质传热和渗流理论,建立考虑相变的饱和地层渗流冻结流热耦合数学模型,利用联络通道冻结模型试验结果验证流热耦合模型的有效性。在此基础上,研究渗流速度、冷媒温度、冻结管直径和渗流温度对联络通道冻结壁形成过程和交圈时间的影响规律。最后,采用正交试验方法对冻结壁形成过程影响因素的显著性进行分析,提出考虑多因素影响的冻结壁交圈时间和标厚时间预测方法。研究结果表明:无渗流时,联络通道冻结温度场呈W型对称分布;当渗流速度为51.2 m/d时,地层温度场不再呈对称分布,上游区域温度高于下游区域温度。渗流速度是影响联络通道冻结壁形成的首要因素,冻结管直径和冷媒温度次之,渗流温度对交圈时间的影响较小。上游侧墙是渗流地层冻结壁扩展的薄弱环节,应加强该区域温度场的监测,跟踪冻结壁的形成过程。

阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响

滑阀流道呈现一种非对称且变化的复杂流道,阀内形成湍流流动,致使阀芯表面受到不均匀压力作用,形成不平衡力,导致阀芯出现倾斜,增加阀芯卡滞的风险,影响滑阀正常工作。针对这个问题,研究了阀体偏心沉割槽对滑阀阀芯径向不平衡力的影响。首先,简化了滑阀流道模型,采用数值模拟方法建立了滑阀瞬态流动分析模型;然后,基于伯努利效应,分析了不同偏心沉割槽时阀芯表面不均匀压力分布规律;最后,获取了不平衡力计算公式,研究了不同沉割槽偏心距对阀内流动特性、阀芯表面受力及径向不平衡力的影响。研究结果表明:采用偏心沉割槽结构减缓了出口段阀芯下表面区域的湍流程度,有效降低了阀芯径向不平衡力的大小;沉割槽偏心距为1.92 mm时,阀芯受到的不平衡力最小,相对于无偏心沉割槽,径向不平衡力在开度为0.5 mm时减小了77.63%,开度为1.5 mm时减小了50.18%,有效减缓了阀芯的倾斜程度。该研究结果对阀体沉割槽设计及阀芯不平衡力抑制方法的研究具有一定参考价值。

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells （ECs） exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.

基于翼型加速流道的多叶离心风机设计方法

在叶轮结构参数优化方法和翼型叶片的研究基础上,本文针对多叶离心风机效率普遍较低的现状提出了一种基于翼型加速流道的多叶离心风机设计方法。该方法通过深入分析翼型结构及叶片出口角参数对加速流道的流动影响,建立了翼型加速流道的风机叶轮设计方法,在此基础上采用考虑粘性的蜗壳设计,形成了多叶离心风机的整体设计流程。将该设计方法应用于某款多叶离心风机设计实例,通过数值模拟结果表明:效率得到了明显的提升,为多叶离心风机的优化设计提供了新的思路和方法。

过江通道围堰绕流场流速分布特性与紊流宽度影响研究

施工期围堰绕流场分布特性是船舶通航安全评估需要考虑的主要问题。选址确定后,围堰绕流场分布特性与来流速度和围堰形状密切相关,研究来流速度和围堰形状对围堰绕流场分布特性的影响对围堰设计与船舶安全通航具有重要意义。文章建立了围堰绕流数值计算模型,采用物理模型试验验证了数值计算方法和网格尺寸的合理性和准确性,针对围堰绕流问题及其对船舶通航安全的影响,分析了围堰形状和来流速度对围堰绕流场流线分布、纵向与横向流速分布特性的影响规律,得到了矩形、哑铃形和圆端形三种围堰形状的导流能力以及施工期桥区船舶安全通航所需的通航净宽。研究结果表明:矩形围堰紊流宽度最大,哑铃形围堰次之,圆端形围堰最小,紊流宽度随来流流速的增大而增大。通航侧碍航紊流宽度介于1.3 D~2.1D。