A Numerical Study on the Effect of the Backflow Hole Position on the Performances of a Self-Priming Pump

A self-priming pump is a centrifugal pump that has the ability to prime itself. Typically, its performance dependson the configuration of its reflux hole. In this study, the ANSYS FLUENT software is used to investigate the effectsof three different radial positions of the reflux hole on gas-liquid two-phase distribution, pressure pulsation, andimp during self-priming. The research results indicate that: (1) The effective channel size for the reflux liquid toenter the volute varies depending on the location of the reflux hole. The effect of the impeller rotation on thereflux liquid becomes more obvious as the setting distance of the reflux aperture decreases. (2) The position ofthe reflux hole significantly affects the gas phase mass fraction inside the impeller, resulting in a significant reductionin the time it takes for the mass fraction to exceed 80%. (3) The position of the reflux hole significantly affectsthe average pressure on each monitoring surface. (4) Placing the reflux hole at a excessively distant radial distancecan result in an excessive vertical component. (5) The self-priming performance of the pump can be improved tosome extent by placing the return hole at a small radial distance.

Performances and Rotating Flows of Rotary Jet Pump

The rotary jet pumps, namely the pitot pumps, are composed of the rotating casing with the impeller channels and the stationary pick-up tube for discharging, are known as the one of high pressure pumps in the U.S. market. The pumps, however, have been prepared experientially, because of poor knowledge for the flow conditions and the pump performances. Then, this paper discusses the pump performances and the internal flow conditions in the rotating casing. Three types of the pick-up tube were prepared for the experiments to know the pump performances and the flow conditions in the rotating casing. The flow in the rotating casing is nearly in the forced vortex type and gives the higher pressure at the pick-up tube inlet. The more cross-sectional area of the pick-up tube channel is large, the more head and discharge are higher with excellent efficiency. Moreover, the authors confirmed that the secondary flow runs toward the rotating center at the wake flow region behind the pick-up tube.

宽式防旋墩环形堰竖井水力特性分析

目前许多拟建抽蓄工程泄洪洞的环形堰竖井入口设置了新型宽式防旋墩,以消除喉口处由不可控漩流引起的呛水等不利流态,而宽式防旋墩环形堰竖井的水气特性与以往采用起旋墩和窄式防旋墩的竖井存在较大差异,业内对其认识尚不清晰。以石台抽水蓄能电站下水库泄洪洞的竖井作为研究对象,采用物理模型试验与数值模拟相结合的手段,分析了流态、流速、压力、消能率等水力指标。研究结果表明:宽式防旋墩引导水流平顺进入竖井形成脱壁流,其尾部可形成顺畅的进气通道,空气经此通道可充分进入竖井以保持井内流态与压力的稳定;新型竖井过流能力满足要求,各部位流速、压力分布正常,总消能率达85%以上;宽式防旋墩可消除不可控漩流导致的呛水现象并引导水流在竖井内形成脱壁流态,使竖井壁面免于空蚀破坏;墩尾通气量足够时,可取消通气管及环形堰与竖井结合部突扩体型,简化工程布置。相关经验可供类似抽蓄电站工程的泄洪洞竖井设计参考。

初始转速与导叶控制策略对变速抽水蓄能机组泵断电过程影响规律研究

在可变速抽水蓄能机组泵断电暂态过程中,因导叶关闭引起的压力波动、回流、转速双峰等不利现象,极大影响了机组及压力管道系统的安全运行;初始转速作为影响机组动态特性的重要参数,其对泵断电过程中转速、流量的影响规律尚不明晰。针对以上问题,基于一维瞬变流理论特征线法和改进Suter变换法,构建可变速抽水蓄能机组调节系统模型。通过对可变速抽水蓄能机组泵断电过程进行模拟,分析了导叶关闭时间对特征参数的影响规律,阐明了初始运行转速与倒流流量、反转转速极值之间的内在联系。结果表明,正转正流阶段和正转逆流阶段的初期各特征参数时域响应趋势极为相近;与此同时,对比不同导叶关闭时间的结果,得出由反转逆流阶段进入停机能够增强机组及压力管道系统安全性的结论;此外,在同一扬程和入力条件下,采用不同初始运行转速对泵断电过程进行模拟,得出流量、转速极值特性与初始运行转速呈负相关的结论。

Effect of inlet elbow on rotation stall in waterjet ppropulsionpump

To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump(WJPP),a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numerically simulated.By comparing the hydraulic performance of WJPP under the two inlet conditions,the internal relationship between the inlet mode and the flow pattern in the pump is clarified.Based on unsteady pressure fluctuation characteristics and wavelet analysis,the influence of the inlet mode on the rotating stall is revealed,and the stall transient propagation characteristics under critical stall conditions are analyzed.The disturbance effects of the inlet channel geometry disappear under low flow rate conditions,the main disturbance is induced by the highspeed countercurrent,and the flow pattern under the elbow inlet is better than that under the straight-pipe inlet.Under the straight-pipe inlet,the single-stall nucleus in the WJPP temporarily experiences a low-frequency and high-amplitude disturbance,which subsequently transforms into a mode of multi-stall nuclei with high-frequency circumferential disturbance.Under the elbow inlet,the rotating stall always maintains a mode of high-amplitude and low-frequency disturbance,which represents the transient characteristics of a single stall core propagating in the circumferential direction inside the channel.The results of this study have a reference value for structural design optimization in a WJPP.

旋壳转速对腔内液体流动特性的效应

为研究旋壳转速对腔内液体流动特性的影响,以试验旋喷泵为研究对象,在高度验证叶轮与旋壳同步旋转试验与模拟结果准确性的基础上,对叶轮转速相同、旋壳转速不同的5个模型采用RNG k-ε湍流模型进行数值计算,分析腔内液体流动特性的变化情况,研究泵的性能.结果表明:旋壳转速增大,液体圆周速度和旋转系数均增大,圆周速度曲线沿径向逐渐形成同心圆,腔内液体做非刚性旋转.腔内液体径向压力梯度增大,压力低于624 kPa时,旋壳转速越高,压力越小;压力高于624 kPa时,旋壳转速越高,压力越大.集流管迎流区涡分布在进口附近,尾迹区涡集中在扩散段结尾处,整体呈增大趋势.旋壳转速增大,泵的扬程升高,但效率降低,通过改变集流管进口直径发现集流管并非效率降低的主要原因,而是由圆盘摩擦损失的增大导致的,圆盘摩擦损失随旋壳转速增加呈3次幂函数式增大,文中最优进口直径为13 mm.

微型高速轴向柱塞泵转子系统力矩损失仿真分析

微型高速轴向柱塞泵转子系统在充满油液的壳体内高速旋转时,产生较大的力矩损失,影响柱塞泵的效率。首先,建立了轴向柱塞泵转子系统力矩损失仿真模型。其次,分析了其力矩损失组成和柱塞泵转速与斜盘倾角对其力矩损失的影响。最后,通过不同切片位置下柱塞泵转子系统油液速度场和压力场分布特点,分析了其力矩损失。结果表明:转子系统压差力矩损失约为其黏性摩擦力矩损失的11倍,其中,柱塞-滑靴压差力矩损失约占70%;随着转角的变化,压差力矩损失波动较大,黏性摩擦力矩损失几乎保持稳定。油液压力呈梯形分布且51.4°周期性剧烈波动,由旋转中心到壳体内壁压力逐渐增大;同时,靠近出油口和下止点位置处,油液压力较小。

Performance Test and Flow Measurement of Contra-Rotating Axial Flow Pump

An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower rotational speed. （2） A stable head-characteristic curve for flow rate with negative slope appears. （3） As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.

Investigation of Self-Priming Process of a Centrifugal Pump with Double Blades

The gas-liquid two-phase flow patterns of a centrifugal pump during the self-priming process were investigated numerically and experimentally.The Euler-Euler multiphase model and SST k-ω turbulence model were applied for simulating the self-priming process.Meanwhile,the changes of motor speed and self-priming height were considered in the simulation.The overall transient two-phase flow features and water level distributions were mapped.Results showed that the self-priming process was divided into three stages.The liquid level in inlet-pipe rose in oscillation during self-priming process.The variations of water level during self-priming process of numerical simulation and test result agreed well.The inlet-pipe(Ver)was filled at 22 s and 24 s respectively numerically and experimentally.The bubble cloud circulated in the volute during middle stage of self-priming process,and breakup into smaller bubbles by shear force and tongue,and then discharged into chamber.The bubbles in the outlet-pipe mainly included bubbly flow and slug flow at the last stage of self-priming process,which is morphologically consistent with the test results.Also,during the self-priming process,the reflux liquid was pressed by blades and fully mixed with gas;that is the way to realizing the function of self-priming.

对旋式轴流泵后置叶轮水力性能分析

为了研究对旋式轴流泵后置叶轮对其水力性能的影响,采用CFD软件对该对旋式轴流泵装置进行数值模拟计算,将前置叶轮与后置叶轮水力特性进行对比分析,研究后置叶轮的进口安放角对整个装置水力特性的影响,最后通过模型试验验证数据的可靠性.结果表明:在设计工况下,对旋式轴流泵扬程为11.32 m,效率为87.57%.在小流量工况下,流量为300 L/s左右泵提前进入马鞍区,此时泵扬程为14.06 m,效率为79.48%;在大流量工况下,流量为440 L/s时,泵装置扬程为2.24 m,效率为54.16%.对旋泵后置叶轮的水流进口冲角要大于前置叶轮的水流进口冲角,导致后置叶轮叶片做功能力增强,后置叶轮扬程增大.改变后置叶轮安放角,特别在小流量工况下,后置叶轮的马鞍区同样提前,后置叶轮的进口液流角几乎相同.研究结果对于对旋式轴流泵后置叶轮的设计和优化提供参考依据.

航空发动机多级滑油泵仿真计算及试验验证

滑油泵作为航空发动机润滑系统重要零部件,其工作性能的好坏直接影响航空发动机的使用安全。同时,转速流量特性及高空特性是评价航空发动机滑油泵工作性能的关键参数。以某型航空发动机多级滑油泵为研究对象,利用PumpLinx仿真计算软件及滑油泵真空试验台,通过仿真计算和试验验证相结合的方式,对多级滑油泵的转速流量特性和高空特性进行分析。结果表明:多级滑油泵的出口流量随转速升高而增大;在不同转速下,随着进口绝对压力的降低,多级滑油泵内部的空化现象不断加剧,含气率不断增大,流量不断减少,且下降幅度越来越大。

斜流泵不稳定特性及旋转失速研究

为研究斜流泵出现的鞍形曲线机理,利用数值模拟的方法对斜流泵进行了研究。通过定常数值模拟得到了鞍形曲线组成部分——扬程骤降段和随后扬程小幅上升段两部分机理。小流量下叶轮轮缘处存在流动分离,并且形成漩涡,导致叶轮出口有效外径的减小,是扬程骤降主要原因。流量继续下降,在叶轮出口靠近轮毂处出现一个大尺度的涡,由于漩涡阻塞作用,导致液流由轮毂向轮缘处偏移,使叶轮内部流态由斜流式转变为离心式,是扬程小幅上升的原因。为研究叶轮出口出现回流的原因,利用非定常数值模拟对导叶进行研究,发现导叶进口处存在失速是斜流式叶轮内部流态转变为离心式的主要原因。同时发现在小流量下导叶进口压力不均匀性是失速核沿圆周方向传播的主要原因。

标准型(三行星轮)复合齿轮转子泵的机理研究

概述了普通齿轮转子泵的结构及工作原理 ,介绍了标准型 (三行星轮 )复合齿轮转子泵的工作原理 ,分析了该泵的力学特性 ,推出了平均流量和瞬时流量公式 ,并对该泵的脉动率进行了分析 ,得出当工作轮的齿数为非 3的倍数时 ,该泵的流量脉动将显著降低的结论。当泵的工作轮及腔体用特殊材料 (如不锈钢或陶瓷 )制作或处理时 ,该泵完全可以用在纯水液压系统。

轴流泵失速工况下非定常流动特性研究

为了研究轴流泵在失速工况下的流动特性,对某原型立式轴流泵进行非定常数值计算,对比分析了设计工况以及失速工况下泵内部典型流动结构与压力脉动特性,揭示了失速工况下低频压力脉动的产生机理,利用真机压力脉动测试验证了数值计算方法的可靠性。研究表明:失速工况下叶片背面的前缘靠近轮缘一侧以及尾缘靠近轮毂一侧存在回流区;设计工况下叶轮进口处以及导叶体中段压力脉动主频为叶片通过频率,叶轮出口部位由于受到动静干涉作用,主频为导叶通过频率,导叶体出口部位由于远离旋转叶轮,叶频主导作用减弱;深度失速工况下泵内部压力脉动系数幅值显著增加,其中导叶体出口处G6点在深度失速工况下压力脉动系数幅值为设计工况的16倍;深度失速工况下叶轮出口处监测点P6、导叶体中段监测点G2以及导叶体出口监测点G6出现频率为0.83 Hz的低频压力脉动;失速工况下导叶体内涡核心区域与导叶流线图中存在的漩涡的发展、演化规律基本一致,两者的频率均为0.86 Hz,与低频压力脉动的频率(0.83 Hz)较为接近,因此可以证明低频压力脉动由导叶内漩涡诱导所致。

旋流自吸泵泵体结构参数的优化设计

采用CFD软件通过大涡模拟,基于正交设计法对旋流自吸泵泵体进行了优化设计,研究了泵体各几何参数对旋流自吸泵性能的影响。设计了一个4因素3水平的正交方案,对数值计算的数据作了极差分析,得到了各几何参数对设计点扬程、效率,最优点的扬程、效率及最大自吸高度5个性能指标的影响的主次顺序。对于数据处理结果,通过综合平衡法分析得出了最优的参数组合。并对得到的最优参数组合进行性能试验,验证了理论计算的可靠性。计算及分析结果对旋流自吸泵性能优化设计具有一定的参考价值。

旋流自吸泵内部湍流场大涡模拟

旋流自吸泵蜗壳结构不同于普通泵,具有特殊的流场结构。采用大涡模拟方法和滑移网格技术,通过对设计工况下旋流自吸泵三维非定常湍流场的数值计算,捕捉到泵叶轮和蜗壳内的压力分布、速度分布和尾迹区内旋涡的结构与演化特征等重要流动信息,结果表明叶轮内部静压具有一定的非对称性。分析了分离室内漩涡形成的原因。对含气率分布的分析表明,叶轮中气相主要集中于叶片的吸力面区域。对旋流自吸泵的性能进行预测,得到了预测性能曲线,并将预测结果与性能试验结果作了对比,证明了大涡模拟法能够较准确地预测旋流自吸泵内部流动特性和性能。

旋流自吸泵内部流场的数值模拟

采用雷诺时均N-S方程和标准k-ε湍流模型,应用三维非结构四面体网格建模,选用旋转流体机械模型中的多重参考坐标系模型(MRF),对设计工况下旋流自吸泵叶轮和蜗壳耦合的三维不可压缩湍流流场进行了数值模拟,得到了其内部流场的压力分布和速度分布情况.对叶轮内部的相对速度流场和压力场进行了细致的分析,证实了叶轮和蜗壳由于相对位置不同,相互作用而引起的叶轮内部流场具有一定的非对称性.对蜗壳速度流场进行了分析,得到了蜗壳内靠近叶轮出口处的速度值较大的结论,并指出,由于蜗壳结构复杂而导致的内部流动紊乱,会造成一定的损失.另外,还对导壁附近区域和分离室内流场进行了深入研究,揭示了导壁附近区域和分离室内存在旋涡这一现象,并对旋涡形成的原因进行了分析和探讨.

轴流泵装置模型断电飞逸过程三维湍流数值模拟

针对轴流泵装置模型断电飞逸过程特点,对应叶轮区所采用的冻结叶轮的变速旋转坐标系方法与基于任意拉格朗日-欧拉方法(ALE)的变速滑移网格法,构建基于三维非定常RANS方程与Spalart-Allmaras湍流模型的数值模拟方法,采用有限体积法对控制方程组进行离散,时间项采用一阶向后差分隐式格式,方程组中扩散项采用二阶中心差分格式,对流项采用二阶迎风格式,应用SIMPLEC方法进行速度压力耦合求解,采用初始工况的定常计算结果作为非定常计算的初始流场.经过轴流泵装置模型断电飞逸过程的数值模拟,获得了机组到达最大转速时所需时间为20.35 s,以及两种数值方法所得最大飞逸转速分别为1 610,1 989 r/min,装置模型稳态飞逸试验转速1 720 r/min,介于两者之间,同时揭示了机组转速、流量、转矩与测点压力等参数随时间变化规律与装置模型流道子午截面流速场、叶轮叶片压力场的瞬变过程,从而为机组结构优化设计和运行管理提供科学的参考依据.

旋流自吸泵气液两相流数值模拟

采用雷诺时均N-S方程和RNGk-ε湍流模型,使用多相流模型中的混合物模型,通过商用软件FLUENT,对自吸时旋流自吸泵内气液两相流场作了数值模拟.在对蜗壳流道和叶轮流道进行网格划分时,尺寸扭曲率为0.78.根据模拟结果,将泵内两相流场的静压分布,与单液相时的静压分布作了对比,并比较了叶轮内气相与液相相对速度的分布情况.另外,对含气率的分布情况作了分析.结果表明,自吸时气液两相状态下的静压稍小于单液相状态下的静压;泵内的主要流动是液相通过相间作用夹带气相的流动,液相速度略大于气相速度;靠近泵出口的两个叶道内,有气相的积聚,含气率较高.

运行工况对离心泵振动影响的试验研究

船用设备的特点是多工况运行,为研究变工况对船用离心泵振动的影响,对离心泵组进行试验研究,从转速、流量等参数变化进行综合分析,试验结果验证转速—振动经验公式,并总结出离心泵振动水平与转速的4～9次幂成正比;流量变化对低、高频振动的影响比中频段的影响更为明显,在特征频率叶频处表现得尤为突出;在需要小流量工况时,应采用调节降低转速代替阀门调节等对离心泵低噪声运行的有利措施。