轴流式混输泵叶片载荷分布特性研究

为了研究气液两相条件下多级轴流式油气混输泵的叶轮叶片载荷分布特性,选用标准κ-ε湍流模型,利用CFD软件探讨了不同工况下轴流式混输泵叶轮叶片压力载荷随含气率及流量变化的规律,并分析了混输泵叶轮内进行能量转化的主要部位。结果表明,当流量一定时,随着含气率的升高,混输泵叶轮叶片工作面和吸力面压力载荷逐渐升高,且小流量工况下叶片压力载荷受含气率变化的影响程度要大于大流量工况;混输泵叶轮前半段在靠近轮毂处的能量转化能力较差,靠近轮缘处的能量转化能力较强,且叶轮前1/3段能量转化能力明显高于叶轮其他段,即混输泵内进行能量转化的主要部位是叶轮前1/3段。     

油气混输泵压缩级内湍流强度及湍流耗散特性分析

为了研究气液两相条件下油气混输泵压缩级内湍流强度和湍流耗散的分布规律,本文以螺旋轴流式油气混输泵为研究对象,采用CFD软件进行数值计算,得到从10%到70%含气率条件下油气混输泵压缩级内的湍流强度和湍流耗散特性。研究表明:气体越集中的位置也是介质流动越不均匀的位置;级间动静干涉作用、流动的不均匀性以及较大旋涡的出现均会导致湍流强度和湍流耗散程度的增加,且在压缩级内随着含气率的增加,湍流强度最大值先减小再增加,且低含气率下湍流强度最大值最大;油气混输泵压缩级内水力损失较大的区域主要集中在级间和导叶内以及叶轮进口区域。     

吸入室对双吸中开泵汽蚀特性的影响

针对双吸中开泵吸入室结构的自由性和复杂性加大了设计难度、改变了叶轮的进口流动环量及均匀度并影响泵的汽蚀性能,采用理论方法研究了叶轮进口环量对汽蚀性能的影响,并对一单级双吸中开式离心泵的吸入室进行了优化改型,用数值模拟和试验方法验证了改进型半螺旋吸入室对叶轮汽蚀特性的改善效果。结果表明,进口稍微带正环量能改善叶轮的汽蚀性能,但正环量加大到一定程度后汽蚀又会逐渐恶化;吸入室对叶轮汽蚀的影响因素包括叶轮进口环量和进口流场的均匀度,改进型的半螺旋吸入室提供了叶轮进口的正环量,并提高了叶轮进口流场的均匀度、大幅降低了泵的必需汽蚀余量。     

三级轴流式油气混输泵内流场压力脉动特性

为研究轴流式油气混输泵含气工况级间相互影响以及流道内压力脉动特性,应用Fluent软件数值模拟了三级油气混输泵在设计流量下的全流场瞬态,获得了混输泵内两相运动特征和流动部件内压力脉动情况,并分析了压力脉动时域和频域。结果表明,动静干涉是产生静压波动的主要因素,静压波动均值从入口到出口逐渐增大,级内动静交界处耦合作用较小,级间动静交界处耦合作用则较为明显。各级压缩单元叶轮进口均为脉动最剧烈的地方,距离叶轮进口越远,压力脉动幅值越小,在叶轮出口达到最小。在压缩单元内,流动方向的压力脉动主频幅值逐渐降低。首级叶轮出口、二级叶轮中间和出口以及末级叶轮中间位置压力脉动频率主要为2倍叶频,其他监测点压力脉动频率均为1倍叶频。气相对压力脉动频率影响较小,仅影响幅值。研究结果可为混输泵的结构优化设计及流动诱导振动控制提供参考。     

颗粒浓度对高比转速离心泵非定常特性的影响

为了分析颗粒浓度对高比转速离心泵非定常特性的影响,采用Mixture混合多相流模型,利用CFX软件进行数值模拟,分析了不同颗粒浓度时的瞬时湍动能、压力脉动及径向力。研究表明:随着颗粒浓度的增加,效率有所下降,清水条件下的离心泵效率最优;随着颗粒浓度的增大,叶轮内的瞬时湍动能明显增强,叶轮流道内及隔舌处的压力值均减小,脉动幅值均增大,作用在叶轮上的径向力会增大,而作用在隔舌处的径向力会减小;在不同颗粒浓度下,叶轮流道内的压力脉动主频均出现在转频处;隔舌处的压力脉动主频出现在叶频处;叶轮流道内、隔舌处的压力值和压力脉动幅值增减速度快慢的分界点和叶轮上、隔舌处的径向力增减速度快慢的分界点均在颗粒浓度为1%附近。     

离心泵仿生叶片的降噪特性研究

采用仿生学思维对离心泵叶片出口进行仿生改造,结合CFD和噪声计算对设计工况下的流场和声场信息进行对比分析,用数值模拟方法验证其结构改进后的降噪效果。计算结果表明：采用仿生结构叶片能够有效的降低隔舌、蜗壳出口和叶轮流道内的湍流脉动强度,同时使流场中的涡结构尺度减小,控制流场中涡结构的分布范围,降低了离心泵内噪声源强度,达到降低噪声的目的。原模型和仿生叶片模型的压力脉动特征频率均为叶频及其低阶倍频,仿生叶片模型在各监测位置的压力脉动均比原模型有明显的降低;仿生叶片使各监测点噪声源强度降低,其出口3倍管径处的降噪效果最佳,总声压级下降3.62 dB,降噪率为3.20%;在隔舌处的总声压级下降1.15 dB,降噪率为0.67%,总体降噪率在0.67%～3.20%,达到了降噪的目的。     

叶轮与隔流板间隙对射流式自吸离心泵性能的影响

为分析射流式自吸离心泵叶轮与隔流板间隙对其性能的影响,采用数值模拟的方法得到了5种该间隙下泵外特性曲线、自吸过程泵内部气液两相分布及流动情况,分析表明:随间隙增大,泵的扬程和效率上下波动较小;叶轮内含气率、导流器出口及泵体出口的气相质量流率随间隙增大而下降。兼顾考虑外特性、自吸性能、加工及装配工艺,确定叶轮与隔流板的间隙为1.0 mm最为理想。样机试验表明:设计点扬程34.21 m,效率55.29%;自吸高度为5 m时,自吸时间45 s,满足设计要求。     

含气率对混流泵压水室流场的影响分析

为了研究含气率对混流泵压水室内的流场影响,以某厂生产的导叶式混流泵为研究对象,应用商业CFD软件进行数值模拟分析,得到在不同份额含气率条件下压水室内部的流场特性。结果表明:混流泵压水室出口处的流速要比其他位置上的流速大,不符合压水室出口处能量转换的定律,而且随着含气率的增大混流泵压水室在径向流道方向上的压力也在不断增大,并在压水室外壁上出现局部的高压现象,这对混流泵压水室强度有一定的考验。在靠近导叶出口处的压水室内有大量的气体聚集,影响混流泵的运行稳定性。     

含气率对多相混输泵叶片应力应变的影响

为了揭示流固耦合作用对多相混输泵的影响规律,以一单级多相混输泵为研究对象,选取气液两相作为运输介质,基于ANSYS软件进行数值计算,流体域采用TurboGrid进行结构化网格划分。通过计算得到不同含气率下叶片表面的应力和应变分布规律。结果表明:在不同含气率下,动叶轮内最大变形量均出现在流向系数为0.1附近,而静叶轮内变形最明显的位置位于叶片的进口与出口处;随着含气率的增加静叶轮内叶片的变形量有一定程度的下降,但降低的程度要低于动叶轮内叶片的变化量。在动叶轮内,随着含气率的增加压力面和吸力面等效应力整体减小,且最大等效应力区域逐渐向叶轮进口方向移动。研究结果可为多相混输泵的开发与结构优化提供参考。     

叶片包角对高比转速离心泵固液两相非定常特性的影响

为了分析叶片包角在固液两相流下对高比转速离心泵非定常特性的影响,采用ANSYS CFX软件和Mixture多相流模型对5种不同叶片包角离心泵的固液两相流进行了非定常数值模拟,分析了叶片包角对固液两相流离心泵瞬时扬程、压力脉动及径向力的影响。研究表明:随着叶片包角每增大10°,固液两相流离心泵的瞬时扬程有所降低,波动时间会延迟0.001 s;流道内及隔舌处的压力值越来越小,脉动幅值越来越大,压力波动时间向后延迟0.001 s;叶轮上的径向力会增大,隔舌处的径向力会减小,受力方均向顺时针偏转;不同包角下的固液两相流离心泵叶轮流道内的压力脉动主频均出现在转频处,隔舌处的压力脉动主频出现在叶频处。其中,叶片包角φ=120°是叶轮流道内压力值和压力脉动幅值增减速度快慢的分界点,也是隔舌处的压力脉动幅值最小值点。     

大型双吸式离心泵内流场空化特性数值模拟分析

为探究大型双吸式离心泵的内流场空化特性,使用CFD技术的数值计算方法,在设计工况下,选用标准κ-ε湍流模型及基于Rayleigh-Plesset方程的输运空化模型,对某大型双吸式离心泵内流场空化特性进行数值模拟,经后处理得到离心泵在不同有效汽蚀余量时内部流动的压力分布、空泡体积分数分布情况,并结合试验结果进行对比分析。结果表明,利用CFD进行三维湍流数值模拟可有效反映出双吸式离心泵内流场的空化特性,数值模拟结果与试验结果较一致,为通过CFD数值模拟方法研究大型双吸式离心泵空化特性提供了参考。     

双吸泵空化非定常数值分析

为了分析双吸泵内部非定常空化流,采用SST湍流模型及基于Rayleigh-Plesset方程的输运空化模型,对双吸泵空化流场进行定常与非定常模拟,得到了双吸泵内流场空化初生部位及空化发展情况,并设置监测点分析了空化状态下双吸泵内不同位置处的压力脉动特性。结果表明,空化首先发生于叶片吸力面头部靠近前盖板处,随着空化余量的降低,空化面积及空泡体积分数不断增大,空化继续发展后,空泡会逐渐向叶片吸力面及叶轮出口扩散,从而降低泵的扬程;在一个旋转周期内,单个叶片上的空化状态呈现出由弱变强、再由强变弱的发展趋势;随着空化余量的降低,监测点处压力脉动幅值增加,蜗壳流道内压力脉动的主频为叶频,谐频为叶频的倍数,且蜗壳隔舌处的压力脉动幅值最大。     

Numerical simulation and experiment analyses for the gas-liquid two-phase vortex pump

Based on the gas-liquid two-phase mixture transportation test,the k-ε-Ap turbulence model was applied to simulate the two-phase turbulent flow in a vortex pump.By comparing the simulation and experiment results,inner flow features were revealed.The bubbles in the channel distribute mainly at the pressure side of the blades,and the aggregation degree of the bubbles is enhanced with an increase in inlet gas volume fraction.Experimental results indicate that the influence of the gas phase on vortex pump performance is small when the gas volume fraction is less than 10%.When the gas volume fraction continuously increases to 15%,the characteristic curves abruptly drop due to the gas blocking phenomenon.     

Pressure fluctuation generated by the interaction of blade and tongue

Pressure fluctuation around the tongue has large effect on the stable operation of a centrifugal pump. In this paper, the Reynolds averaged Navier-Stokes equations (RANS) and the RNG k-epsilon turbulence model is employed to simulate the flow in a pump. The flow field in the centrifugal pump is computed for a range of flow rate. The simulation results have been compared with the experimental data and good agreement has been achieved. In order to study the interaction of the tongue with the impeller, fifteen monitor probes are evenly distributed circumferentially at three radii around the tongue. Pressure distribution is investigated at various blade positions while the blade approaches to and leaves the tongue region. Results show that pressure signal fluctuates largely around the tongue, and it is more intense near the tongue surface. At design condition, standard deviation of pressure fluctuation is the minimum. At large flow rate, the increased low pressure region at the blade trailing edge results in the increases of pressure fluctuation amplitude and pressure spectra at the monitor probes. Minimum pressure is obtained when the blade is facing to the tongue. It is found that the amplitude of pressure fluctuation strongly depends on the blade positions at large flow rate, and pressure fluctuation is caused by the relative movement between blades and tongue. At small flow rate, the rule of pressure fluctuation is mainly depending on the structure of vortex flow at blade passage exit besides the influence from the relative position between the blade and the tongue.     

Simulation of Convective Heat Transfer of Gas–Liquid Bubble Train Flow in Wet Microtube

In this paper, a direct numerical simulation of a two‐phase incompressible gas–liquid flow for simulation of bubble motion and convective heat transfer in a microtube is presented. The microtube radius is 10 μm. The interface between the two phases is tracked by the volume of fluid method with the continuous surface force model. Newtonian flows are solved using a finite volume scheme based on the PISO algorithm. Numerical simulation is done on an axisymmetric domain with a periodic boundary condition for different values of pressure gradient, void fraction, and bubble period. Mean pressure gradient is fixed for each simulation. The superficial Reynolds numbers of gas and liquid phases studied are 0.3 to 7 and 5 to 210, respectively. Numerical results are coincident with the Serizawa regime map, and there is a linear relation between the void fraction and gas flow ratio. Simulation shows local Nusselt number increases in the presence of a gas bubble.     

圆管内油-气-水三相弹状流液弹区流动特性的研究

利用液弹内气体平衡关系，建立油－气－水三相流液弹平均含气率的物理模型。同时利用光导纤维探针法，详细测定各种工况下稳态弹状流液弹的含气率局部分布规律；并通过变换探针的径向位置，研究液弹含气率沿液弹长度的空间变化规律，从细观上揭示油、气、水三相弹状流流弹区流动特性。     

颗粒体积分数对天然气水合物多相混输泵内流特性的影响

为研究颗粒体积分数对天然气水合物多相混输泵内流特性的影响,基于ANSYS CFX软件采用非均相模型和particle模型,选用甲烷水合物颗粒体积分数为5%、10%、15%和20%的海水为介质,对多相混输泵流场进行数值模拟。结果表明：当颗粒体积分数较低时多相混输泵叶轮和导叶内旋涡较小,但随着颗粒体积分数的增加多相混输泵叶轮和导叶内轴向旋涡逐渐增大;在叶轮流道内颗粒分布较为均匀,而随着颗粒体积分数的增加,导叶内较大的旋涡影响导致颗粒在导叶内出现明显的聚集现象,在导叶叶片表面颗粒主要聚集在吸力面前半部分,其分布区域远大于压力面,即导叶吸力面更易受到磨损;随着颗粒体积分数的增加,多相混输泵的扬程和效率均逐渐降低。     

Investigation on the void fraction of gas–liquid two-phase flows in vertically-downward pipes

A special experimental loop is designed and constructed to study the characteristics of the void fraction of gas–liquid two-phase flow in vertically-downward pipes. The test section is made of transparent pipe with a length of 6 m and an internal diameter of 25 mm. The void fraction ranging from 0.1 to 0.98 widely is measured using quick-closing valve method. It is found that the range of the void fraction could be divided into three regions with different flow patterns and different relationships between the void fraction and the gas–liquid volumetric flow rate ratio. Moreover, 39 correlations for calculating the void fraction collected from present literature, are classified, and evaluated using the experimental data obtained in this study. The prediction of correlations in the literature needs to be improved when the void fraction is small.     

A void fraction model for annular flow in horizontal tubes

An important feature of detailed system simulation models for unitary air conditioners is the calculation of charge inventory. Void fraction determination in the two-phase regions of the heat exchangers is the primary challenge associated with charge inventory calculations. Annular flow is one of the predominant flow regimes encountered in horizontal heat exchangers. Analytical annular flow models typically fail to accurately represent void fraction. Thus, many of the available void fraction models are empirically based. To improve the prediction capabilities of void fraction models, a mechanistic void fraction model has been developed for annular flow in horizontal tubes. The present model considers the effect of momentum eddy diffusivity damping at the liquid-vapor interface. Two approaches are presented for determining the wall shear stress. The modeling results are compared to predictions from various void fraction models found in the literature. The present model is found to work well at moderate mass fluxes.