诱导轮出口螺距对离心泵空化性能的影响

为了查明诱导轮出口螺距对离心泵空化性能的影响,设计了入口螺距相同、出口螺距逐渐增大的三个诱导轮:诱导轮5-5、诱导轮5-8、诱导轮5-11;采用k-ε湍流模型和Singhal空泡动力学模型,对泵内流动进行空化数值模拟,分析了设计工况下离心泵空化断裂特性和气泡分布流场特征。结果表明:相比于等螺距诱导轮5-5,加设变螺距诱导轮5-8及5-11的离心泵在相同进口压力条件下具有更高的扬程和更少的流场内气泡分布,在同一流量工况下具有更低的空化断裂点,在空化断裂点泵扬程分别提高了10.4%和18.6%;变螺距诱导轮保持进口螺距不变,增大出口螺距可以进一步提升半开式叶轮离心泵抗空化性能。     

诱导轮和离心泵叶轮内部空化流动数值分析

为了提高诱导轮离心泵的空化性能和运行稳定性,阐明诱导轮和离心泵叶轮几何参数对空化性能的影响规律,基于空泡可压缩性影响修正的RNG k-ε模型和改进的空化模型,对诱导轮和离心泵叶轮内部流场进行空化数值计算。数值结果表明:在小流量工况和额定工况下,空化性能曲线基本一致;在大流量工况下,空化特性曲线波动相对比较严重,空化性能较差。额定流量下泵蜗壳水力损失最小,小流量工况下蜗壳水力损失最大。临界汽蚀余量时,蜗壳水力损失突升。无空化条件下,随着前口环间隙值的增大,诱导轮扬程、效率和前口环间隙泄漏量增大,泵和叶轮的扬程、效率值降低,泵的空化特性曲线的稳定性变差,使诱导轮叶片出口液流角发生偏转,导致诱导轮和离心泵叶轮内部产生周期性的交变空化流。     

诱导轮叶片开缝对高速离心泵空化性能的影响

为研究诱导轮叶片表面开缝对高速离心泵空化性能的影响规律,设计叶片开缝系数k为0(叶片未开缝)、6.7%、13.3%、20%和26.7%五种叶片开缝方案。基于RNG k-ε湍流模型和Reyleigh-plesset空化模型对高速离心泵进行全流道三维数值模拟,对比分析了诱导轮截面内流线和压力分布规律、诱导轮内空泡发展过程及离心泵的空化特性曲线。研究结果表明诱导轮叶片入口轮缘处开缝可减小亦或是消除该区域的低压区,且对离心泵的水力性能的影响较小;缝隙可抑制并减小初生空化阶段空泡体积分布;开缝系数k对高速离心泵空化性能的影响存在最优值,该研究中开缝系数k=13.3%时,诱导轮的空化性能表现最优。     

高抗汽蚀性能泵的设计和试验研究

本高抗汽蚀性能泵的NPSH_r=0.54～1.41 m,首级叶轮前装有一个3叶片的变螺距诱导轮。试验研究表明,在普通叶轮前加装诱导轮只能在有限程度上提高泵的抗汽蚀性能,只有诱导轮和主叶轮匹配设计,也就是考虑诱导轮出口流动与叶轮进口流动良好配合,设计的主叶轮才能更有效地提高泵的抗汽蚀能力。     

叶片进口冲角对离心泵空化特性的影响

基于ANSYS CFX软件应用标准k-ε湍流模型、均质多相模型和Rayleigh-Plesset方程对一比转数为89的模型泵在冲角变化时泵内的空化流场进行数值模拟.根据计算结果预测了模型泵无空化时的能量特性和空化时的空化性能,并分析了空化状态下叶轮中间流面上的空泡体积分布和叶片中间流线的载荷特性.研究表明,模型泵叶轮叶片冲角变化时,对设计点的扬程和效率影响不大,对于空化性能则存在一个最优值,不是冲角越大越好.     

高抗气蚀离心泵内流场数值模拟研究（英文）

本文以同一工况下具有相同进出口尺寸的离心泵模型为对象,基于数值模拟的方法研究了子午面轮廓和长短叶片对离心泵的气蚀性能和水力性能影响。遵循抗空化设计准则提出有别于普通离心泵的三种高抗气蚀离心泵,其一具有驼峰型过水断面曲线,最大值在叶片前缘处以降低前缘冲击损失,减少空化影响。其二采用诱导轮叶轮一体化设计,安置分流叶片,长叶片在进口处螺旋形前伸,提前做功,使低压点前移。其三结合以上两种设计手段综合提高抗气蚀性能。采用多相流CFD模型预测三种模型泵在设计工况下的气蚀性能叶片载荷与气液两相分布间,并在无量纲空化数下分析了其气蚀性能。结果显示进口延长的螺旋形长叶片形成了类似诱导轮的效果,降低了整个叶轮对空化影响的敏感性。另一方面,单纯地扩展子午面流道虽然可以显著提高扬程与空化性能,但是却对整体效率产生了不利影响。     

变螺距诱导轮的设计计算方法

诱导轮是一种叶片负荷很小的轴流叶轮,由于它本身具有很高的抗汽蚀性能,所以把它装在离心叶轮前面进行增压,可以提高整台泵机组的抗汽蚀性能。常用的诱导轮是螺旋诱导轮,其中以平板式等螺距诱导轮用得最多。但是,等螺距诱导轮在水力性能方面是不完美的,因为它的螺距从入口到出口不变,就不能按常用的设计准则来设计出最满意的诱导轮。采用变螺距诱导轮,正是针对等螺距诱导轮的     

转套式配流系统凸轮槽型线对空化特性的影响

空化引起的振动和噪声会影响转套式配流系统性能和寿命,转套的凸轮槽型线与空化特性关系密切。在线性凸轮槽型线基础上提出了3种新的凸轮槽型线,建立了相应的型线方程,随着曲轴转动,线性型线对应的转套转角波动最小、样条型线最大。建立了系统空化流体力学模型,通过仿真,发现4种型线对应的最大气体体积分数均随工作转速升高单调递增,总体看来线性型线最好;空化占比随转速增大而升高,同转速条件下线性凸轮槽型线对应空化占比最小;容积效率随转速增加单调递减,开始比较平缓,速度较高时降低较快,总体看来线性型线对应的容积效率最高。     

诱导轮性能影响因素的数值模拟及试验研究

诱导轮汽蚀性能是提高泵抗汽蚀性能的关键因素,也是降低火箭发动机储箱重量的关键因素。本文采用ANSYS Fluent软件对9种不同叶片进出口安装角变螺距诱导轮方案进行了数值模拟计算,全面分析了叶片进口、出口安装角对诱导轮水力性能及汽蚀性能的影响规律。同时通过水力试验台采用2台基础泵分别对9个诱导轮方案进行水力性能和汽蚀试验,获取了诱导轮叶片进口、出口安装角对泵水力性能及汽蚀性能在水介质下的影响规律,为设计高汽蚀变螺距诱导轮提供了依据和经验。     

带诱导轮的离心式航空燃油泵空化特性分析

为了研究离心式航空燃油泵空化流场特性,基于RNG k-ε湍流模型与ZGB空化模型,对某带诱导轮的离心式航空燃油泵三维内流场进行了数值计算,分析了诱导轮与离心叶轮叶片表面的空化区演变、燃油泵内部不同过流部件中的空泡区占比、叶顶泄漏涡空化、回流涡空化等流动现象。结果表明,诱导轮对空化的抑制有积极作用,三种不同工况下的空化余量NPSH值一样;诱导轮叶片表面的空化包括叶顶空化、云空化、叶梢空化等不同类型;空化数σ=0.0953时为临界空化点,诱导轮与叶轮区的空泡体积占5%～10%;回流涡空化首先产生于诱导轮叶顶背面附近,随着空化数的降低,回流涡空化区逐步与云空化融合;无论有无空化,燃油泵进口段始终存在明显的二次流。     

磁头磁盘系统动特性参数及系统稳定性分析

对硬盘系统的动特性进行了数值仿真，其中磁头结构为IBM3370，润滑模型中引入了二阶泊松流因子，保证建模精度。利用摄动法建立了气体润滑的静态方程，并给出了数值解。讨论了最小膜厚度、磁盘转速和磁头倾角对空气膜刚度系数、阻尼系数以及对系统稳定性的影响。结果表明，通过最小膜厚度、磁盘转速和磁头倾角的优化可以改善硬盘的设计。其中磁头倾角的优化可以同时满足硬盘高刚度和高稳定性的要求。     

诱导轮内流场数值计算及汽蚀特性分析

为得到诱导轮内部的速度场、压力场及湍流场的分布规律,在基于SIMPLEC算法上,采用了雷诺时均Navier-Stokes方程(简称N-S方程)控制方程和修正了的k-ε湍流模型,对两种结构参数的双叶片诱导轮进行了内部三维不可压湍流流动数值计算。计算结果表明诱导轮最容易发生汽蚀破坏的位置在进口外缘处,计算结果还表明增加诱导轮叶片轴向距离及导程有利于提高诱导轮的汽蚀特性。同时进行了不带诱导轮和带两种结构参数诱导轮的离心泵的外特性试验,试验结果表明离心泵在没有诱导轮的情况下较易发生汽蚀,而增加诱导轮能够明显改善离心泵的汽蚀性能,诱导轮的导程、叶片轴向长度、及其叶尖包角几何参数值等几何参数对汽蚀性能有较大影响。结合流场数值计算结果和试验研究结果,证实了通过增加轴向距离和导程等合理改变结构参数可提高诱导轮的汽蚀性能。     

Numerical simulations and surrogate-based optimization of cavitation performance for an aviation fuel pump

We used computational modeling to investigate the cavitation performance of an aviation fuel pump, and optimize structural parameters using the surrogate-based method. In the numerical simulation, a rotation-curvature correction was adapted to the k-ε turbulence model, and a four-component surrogate fuel was selected to reproduce the physical properties of the China RP-3 kerosene. Then the performance of the aviation fuel pump was predicted. In the optimization, based on the series of the numerical results, Surrogate-based analysis and optimization (SBAO) was used to optimize the structural parameters of the fuel pump (the variation of the outlet blade angle for the inducer △β _b1 and the variation of the inlet blade angle for the impeller △β _b2). The results show that the prediction of cavitation performance agrees well with the experimental data. The results show that cavitation areas are mainly distributed in the inlet of the inducer. The volume of cavities grows with the decreasing NPSHa. The head of the fuel pump has a sudden head-drop when NPSHa ≤ 5.64 m. Furthermore, the surrogate-based approach is available in structural optimization of the fuel pump. The cavitation performance of the optimized pump improved about 22 % with a little drop of head coefficient when △β _b1 = 4.33° and △β _b2 = 3.24°. The numerical approach employed in this paper can accurately predict the cavitating flow of the high rotating speed fuel pump and the surrogate-based method is available in the structural optimization for a better cavitation performance.

     

Head geometry effects on pneumatic three-hole pressure probes for wide angular range

Recent investigations Argüelles et al. (2008) [5] have demonstrated that it is possible to increase the operative angular range of pneumatic three-hole pressure probes (THP) using a two-zoned method in the data reduction procedure. In this study, the influence of the head geometry on the performance of this type of probes is addressed, especially in the extended regions of the angular range, previously unconsidered in the literature. Three different geometries have been built to carry out the analysis, corresponding to cylindrical, trapezoidal and cobra type probes, with a separation angle of 60° between the holes. Additionally, cylindrical and cobra type probes have been manufactured with angular distances of 30° and 45° between the holes, in order to advance the effect of the construction angle on the probes performance. The uncertainty transmitted from the measurements to the resultant flow variables has been also addressed. Moreover, the sensitivity of the different head designs to variations in the Reynolds number or deviations of the flow with respect to the measurement plane of the probe (pitch misalignments) has been addressed. Major conclusions indicate that cobra type probes provide the largest operative angular range, while cylindrical designs minimize the errors in the determination of both pressure and velocity flow variables when the Reynolds number or the pitch angle differ from the baseline calibration.     

高速泵诱导轮的设计分析

本文通过分析诱导轮设计的理论基础,建立了比较完善的诱导设计方法,给出了其主要参数的计算公式,按照本文方法设计的两台高速泵诱导取得了很好的汽蚀性能。     

Effects of the number of inducer blades on the anti-cavitation characteristics and external performance of a centrifugal pump

Installing an inducer upstream of the main impeller is an effective approach for improving the anti-cavitation performance of a highspeed centrifugal pump. For a high-speed centrifugal pump with an inducer, the number of inducer blades can affect its internal flow and external performance. We studied the manner in which the number of inducer blades can affect the anti-cavitation characteristics and external performance of a centrifugal pump. We first use the Rayleigh-Plesset equation and the mixture model to simulate the vaporliquid flow in a centrifugal pump with an inducer, and then predict its external performance. Finally, we tested the external performance of a centrifugal pump with 2-, 3-and 4-bladed inducers, respectively. The results show that the simulations of external performance in a centrifugal pump are in accordance with our experiments. Based on this, we obtained vapor volume fraction distributions for the inducer, the impeller, and in the corresponding whole flow parts. We discovered that the vapor volume fraction of a centrifugal pump with a 3-bladed inducer is less than that of a centrifugal pump with 2-or 4-bladed inducers, which means that a centrifugal pump with a 3-bladed inducer has a better external and anti-cavitation performance.

     

Numerical simulation and experimental research on the influence of solid-phase characteristics on centrifugal pump performance

The law governing the movement of particles in the centrifugal pump channel is complicated; thus, it is difficult to examine the solid-liquid two-phase turbulent flow in the pump. Consequently, the solid-liquid two-phase pump is designed based only on the unary theory. However, the obvious variety of centrifugal-pump internal flow appears because of the existence of solid phase, thus changing pump performance. Therefore, it is necessary to establish the flow characteristics of the solid-liquid two-phase pump. In the current paper, two-phase numerical simulation and centrifugal pump performance tests are carried out using different solid-particle diameters and two-phase mixture concentration conditions. Inner flow features are revealed by comparing the simulated and experimental results. The comparing results indicate that the influence of the solid-phase characteristics on centrifugal-pump performance is small when the flow rate is low, specifically when it is less than 2 m3/h. The maximum efficiency declines, and the best efficiency point tends toward the low flow-rate direction along with increasing solid-particle diameter and volume fraction, leading to reduced pump steady efficient range. The variation tendency of the pump head is basically consistent with that of the efficiency. The efficiency and head values of the two-phase mixture transportation are even larger than those of pure-water transportation under smaller particle diameter and volume fraction conditions at the low-flow-rate region. The change of the particle volume fraction has a greater effect on the pump performance than the change in the particle diameter. The experimental values are totally smaller than the simulated values. This research provides the theoretical foundation for the optimal design of centrifugal pump.     

Metrological atomic force microscope using a large range scanning dual stage

We developed a metrological atomic force microscope (MAFM) using a large range scanning dual stage and evaluated the performance in the measurement of lateral dimension. AFMs are widely used in nanotechnology for very high spatial resolution, but the limitation in measurement range should be overcome to expand its application in nanometrology. Therefore, we constructed new MAFM having a large measurement of 200 mm × 200 mm by using a dual stage and an AFM head module. The dual stage is composed of a coarse and a fine stage to obtain large scanning range and high resolution simultaneously. Precision surfaces and PTFE sliding pads guide the motion of coarse stage, drove by a fine pitch screw and DC motors. Flexure hinges and PZT actuators are utilized for the fine stage. Multi-axis interferometers measure the five degrees of freedom motion of the dual stage for the position control and the compensation of parasitic angular motions. The vertical displacement of AFM tip is measured by a built-in capacitive sensor in the AFM head module within the range of 38 μm. The performance of the dual stage was evaluated and the expanded uncertainty (k = 2) in the measurements of 1-D displacement L was estimated as $ U(L) = \sqrt {(2.8nm)^2 + (3.0 \times 10^{ - 7} \times L)^2 } $ U(L) = \sqrt {(2.8nm)^2 + (3.0 \times 10^{ - 7} \times L)^2 } . The relative uncertainty in pitch measurement was less than 0.02 % and the improvement of accuracy was verified by comparing with other MAFM, which are mostly due to the expansion of scan range and the compensation of angular motion. To enhance the performance, we will reduce the vibration and examine the motion of stage in the vertical direction during a long range scan.     

变螺距双螺杆压缩机性能分析

针对双螺杆压缩机螺距更改时其性能参数的变化,首先,探索双螺杆压缩机性能主要影响因素,并推导主要因素接触线长度、泄漏三角形面积以及面积利用系数的计算公式;然后,使螺杆的螺距按照一定规律的变化,分析螺距变化对双螺杆压缩机性能的影响,通过MATLAB绘制螺杆的螺旋展开线并对螺旋线连续性进行分析;最后,得到一段式、两段式、三段式变螺距螺杆转子对压缩机性能的影响。结果表明,中间段变螺距对双螺杆压缩机性能有明显的提升效果。     

The reconstruction of helical particles with variable pitch

In the reconstruction of helical particles, it is normally assumed that translation along the length of a particle is coupled to rotation about its axis. This assumption is not valid for particles whose pitch varies along the particle length (e.g. actin, HbS fibers), and application of the usual algorithms results in significant errors in both the shape and coordinates of subunits in the reconstructed density map. We have developed an iterative procedure for reconstructing particles with variable pitch. The goal of this procedure is to obtain an accurate estimate of the local pitch of the particle which can then be incorporated into the reconstruction algorithm. This involves synthesis of trial model structures which have constant pitch. The local pitch is derived from a cross-correlation analysis between these trial models and the variable pitch particles. The constant pitch models are constructed using coordinates measured from the reconstructed density maps. Each iteration of the procedure provides an improved estimate of the pitch which is incorporated into the succeeding iteration. The fidelity of the reconstruction is determined from cross-correlation between the original micrograph and a variable pitch model. The iterations are continued until the cross-correlation coefficient between the variable pitch model and the micrograph of the particle is maximized. The implementation of the iterative procedure is described and its behavior is evaluated using model structures which incorporate variations in pitch similar to those actually occurring in sickle hemoglobin fibers. The results indicate that the iterative reconstruction procedure considerably reduces the errors associated with constant pitch reconstructions. These tests provide a basis for applying this procedure in the structural analysis of micrographs of helical particles which display variable pitch. Application to sickle hemoglobin fibers resulted in an improvement in the accuracy with which the hemoglobin S molecules can be located in the density maps.