极大流量工况下离心泵内部流场数值分析

针对离心泵极大流量工况下内部流动特性的问题,应用流体动力学软件Fluent,采用RNGκ-ε湍流模型与SIMPLEC算法,对某一高比转速离心泵内部流场进行了数值模拟,并与实验结果进行了比较。对比分析了4种不同流量工况下离心泵内部流体速度和压力分布以及离心泵的外特性。研究结果表明,在设计流量工况下,离心泵内部压力分布均匀,速度迹线平滑;较大流量工况下,蜗壳压力不断减小,速度分布不均匀;极大流量(1.7Qopt)工况下,蜗壳出口处出现局部负压现象,速度流线产生的漩涡增大,在扩散管局部位置流体受到冲击,容易出现回流现象。针对离心泵在不同工况下以及达到极大流量工况下内部流动随流量变化规律的研究,可为高比转速离心泵多工况优化设计、延长使用寿命提供参考。     

离心泵叶轮区瞬态流动及压力脉动特性

目前离心泵过流部件的瞬态流动分析主要集中在蜗壳内,对旋转叶轮区内的流动特性研究较少。基于RNG k-ε湍流模型和滑移网格,对不同工况下离心泵内部瞬态流场进行数值模拟,计算得到的离心泵扬程和效率曲线与试验结果吻合较好。在离心泵叶片正背面分别设置3个监测点,分析叶轮区压力脉动特性。结果表明,设计工况下叶片正背面压力脉动的主频为叶轮转频或2倍叶轮转频,非设计工况下其主频均为叶轮转频。从叶轮进口到出口,叶片正背面的压力脉动最大幅值都逐渐增大。同一监测点上压力脉动最大幅值在小流量时最大,约为设计工况下5倍。分析小流量工况下叶轮内部相对速度分布,叶轮出口处附近随时间变化的旋涡是内部流动不均匀的主要原因,使得离心泵在该工况下运行效率低、压力脉动强度大。     

双流道泵输送固液介质的水力性能及磨损试验研究

为分析固液混合物对双流道输送泵性能的影响,采用平均粒径为10 mm和36 mm的固体颗粒对双流道泵在不同浓度和流量下开展输送固液两相介质的水力性能试验,并对泵的磨损进行分析。水力试验结果表明,在一定的流量下,随着输送混合物中固体颗粒浓度的增加,入口表压、出口表压、扬程及效率呈递减趋势。 与输送清水时比较,当输送固液两相介质时,随着流量的增大,轴功率上升较快,扬程的下降量在不同流量下几乎相同;效率曲线在不同流量下比输送清水时效率要低,差值随着流量的增大而增大。在同流量同浓度比工况下,泵的进出口压力、扬程和汽蚀性能在输送较大直径固体颗粒时,明显下降。通过对双流道泵磨损的分析表明,叶轮磨损部位主要在前盖板外缘、流道内偏前盖板的流道表面、压力面进口边,压力面的磨损区域呈三角形;泵体的磨损部位主要在周壁、隔舌及泵体口环处。本研究可为固液两相双流道离心泵的理论研究与设计应用提供试验依据。     

固液两相离心泵内部非定常流动特性研究

为研究固液两相流离心泵内部的非定常流动特性,基于滑移网格方法,采用RNGκ-ε湍流模型以及ASMM代数滑移混合物模型,对一台高比转速固液两相离心泵内部流场进行非定常流动的数值模拟,通过分析清水工况数值计算结果、外特性性能实验结果以及固液两相流非定常数值计算结果,获得了非定常条件下固液两相输送离心泵的瞬时外特性曲线和内部流动及磨损规律。研究结果表明:在一个转动周期内,离心泵的扬程、效率和轴功率均呈现正弦波动特征;动静干涉效应使得叶轮出口处的速度和静压分布均呈现周期性波动;模型泵叶轮前后盖板的磨损情况比蜗壳壁面的磨损严重。上述计算结果可为实现高比转速固液两相流离心泵的优化水力设计和减轻磨损提供一定的理论参考。     

离心泵偏工况下流动结构分布及演化特性研究

为了研究离心泵不同工况下的流动分离现象,本文以低比转速离心泵为研究对象,基于LES数值计算探索了泵内不同工况下的流动结构,利用在闭式试验台的性能试验来验证数值计算的准确性,发现泵最高效率点在1.1Qd左右,在设计流量下,LES计算误差小于1.5%。通过叶轮出口流场结构分布特点,对不同工况下的流动分离现象进行对比分析,获得叶轮扫掠隔舌过程中出口流动分离现象的变化特性,及其对叶轮内流场结构的影响。结果表明：流动分离现象表现为分离泡会在叶片表面形成回流,使叶轮出口流动呈现不均匀分布特性,加强射流-尾迹结构。特别在小流量工况下,流动分离为出口旋涡的旋转提供能量,造成出口流道大面积堵塞,堵塞面积可达55%左右,诱发小流量的驼峰现象。     

基于CFD/CA声比拟分析的两级离心泵流动诱导噪声数值模拟

针对两级离心泵的流体诱发噪声产生的复杂机理,基于Lighthill声比拟理论,采用了计算流体力学(CFD)与计算声学(CA)结合的数值模拟分析方法,研究了两级离心泵变工况下的流场特性及诱发的辐射噪声。采用SST k-ω模型计算分析了不同工况下两级离心泵内部非稳态流场及关键区域压力脉动特性,进而采用声学有限元法(AFEM)计算离心泵内场辐射噪声的声压级变化。研究结果表明,两级离心泵压力脉动幅值从吸水室进口到叶轮出口逐渐增大,叶轮出口处的压力脉动强度最大、声压级最高,且不同工况下压力脉动的主频保持为叶频及其倍频,叶轮和蜗壳之间的动静干涉是流动诱导噪声产生的主要原因;总体声压级在低流量工况下较高,随流量增大逐渐减小,在设计工况处最小;越接近压力脉动主频,声压级的分布越离散,宽频特性越明显,压力脉动强度为流动诱导噪声产生的主要影响因素。研究结果对两级离心泵的低噪设计和水力性能改善提供理论依据和参考。     

k-ε涡粘湍流模型用于离心泵数值模拟的适用性

以IS80-65-160离心泵为研究对象,对设计工况和八种非设计工况进行了整机系列相对位置定常流动数值模拟.计算中分别采用标准k-ε模型、RNG缸k-ε模型和Realizable k-ε模型三种k-ε涡粘湍流模型,以考察比较它们对离心泵内流模拟计算的适用性.计算中考虑了叶轮和蜗壳之间相对位置变化对流场的影响,较全面反映叶轮与蜗壳间的相互作用.在数值模拟的基础上,计算了基于三种湍流模型的扬程、轴功率、效率及性能曲线,并与试验性能曲线进行对比.研究表明:三种肛k-ε涡粘湍流模型均可用于离心泵内部流动数值模拟计算,采用Realizable k-ε模型的离心泵仿真结果与试验吻合最好.     

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。     

离心泵径向力的数值模拟与实验研究

在泵装置设计中,径向力的大小一直是人们所关心的问题。基于Fluent流体商用软件对一种离心泵的内流场进行数值模拟。比较径向力数值模拟结果与实验值,发现最大误差为8.1%,误差在设计流量工况下最小,测量精度最高,并且各流量工况下平均误差为4.34%,证明数值模拟预测离心泵的径向力是可行的。将离心泵数值模拟与实验的流量扬程曲线进行对比,趋势比较一致,误差不超过8.3%。在此基础上根据提出的径向力计算模型计算出泵在各流量工况下径向力的大小和方向。针对离心泵内部结构特征研制了一种径向力测量装置,开展径向力测量试验,得到了各工况下径向力的大小。     

基于DES的离心泵内部瞬态流动数值研究

为了阐明变工况运行条件下离心泵内部瞬态流动特性,评价其瞬态水力性能及其压力脉动特性,提高离心泵的运行稳定性,基于DES分离涡模型,在小流量、额定流量和大流量工况下对泵进行了性能预测和数值模拟。与试验结果比较发现,性能预测结果和试验结果吻合较好,额定工况下泵内部流动参数梯度变化均匀。在此基础上,在泵内部设置p1～p9压力脉动监测点,通过对监测点的压力脉动时频分析,表明进口流道p1压力脉动频率与叶频的倍频保持一致,以低频脉动为主;受隔舌结构影响,出口流道p6压力脉动频率的脉动幅值较大,以高频脉动为主。比较叶轮旋转第1～第6圈静压分布和涡量分布规律,第3圈后叶轮内部流动趋于稳定,第6圈后蜗壳内部流动达到稳定,表明离心泵叶轮和蜗壳内部涡团的演化过程非同步。     

Phase discrimination and a high accuracy algorithm for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump

PIV technology is an efficient and powerful measurement method to investigate the characteristics of fluid flow field. But for PIV particle image post-processing, some problems still exit in two-phase particles discrimination and velocity field algorithm, especially for high-speed rotating centrifugal slurry pump. In this study, through summarization and comparison of the various phase discrimination methods, we proposed a two-phase identification method based on statistics of gray-scale level and particle size. The assessment of performance through experimental PIV images shows that a satisfying effect for particle identification. For high speed rotation of the impeller, a combination of adaptive cross-correlation window deformation algorithm and multistage grid subdivision is presented. The algorithm is applied to experimental PIV images of solid–liquid two-phase flow in a centrifugal slurry pump, the results show that the algorithm in the present study has less pseudo vector number and more matching particle pairs than those of fixed window and window translation methods, having the ability to remove pseudo vector efficiently. It confirmed that the algorithm proposed in the present study has good performance and reliability for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump.     

大颗粒下螺旋离心泵内运动特性数值模拟与分析

以150×100LN-32型螺旋离心泵为模型,采用欧拉多流体、RNG k-ε模型对其内部进行三维数值模拟。对比不同颗粒粒径以及浓度情况下固液两相流场,分析了在大颗粒情况下,固体颗粒在螺旋离心泵内的运动情况。通过固相体积分数、压力以及速度分布,得出了大颗粒固液两相流在螺旋离心泵内的运动特性。并以此为参照,分析大颗粒情况下螺旋离心泵磨损情况。     

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.     

多级离心泵扬程预测及内部流场数值模拟

为了研究多级离心泵的性能及其内部流场分布,采用SST k-ε湍流模型对原型泵的首级、第二级及第三级叶轮进行定常和非定常数值模拟计算,分析其外特性、内部流场和压力脉动。研究表明,通过前三级叶轮的扬程能较准确地预测原型泵的扬程。不同流量工况下隔舌处均易出现低压区域,大流量工况蜗壳出口近隔舌处也易出现局部低压区和高压区,隔舌处压力梯度较大。小流量下首级叶轮近隔舌区域的压力脉动不稳定,周期性较差,频域幅值主要集中在低频率区域;对于设计流量和大流量工况,首级叶轮近隔舌区域和远离隔舌区域的压力脉动较为稳定,呈现出较明显的周期性,主频在1倍和2倍叶片通过频率处,频域幅值主要集中在叶片通过频率及其高次谐波频率处。     

离心泵内部空化流动的定常数值模拟及性能预测

为了研究离心泵内部的空化流动,利用fluent软件中的空蚀模型及混合流体两相流模型,对离心泵的三维湍流空蚀流场进行定常数值模拟,根据模拟计算结果显示的液相和空泡相流动特征,预测了离心泵在设计工况下运行时流道内空化发生的位置和程度;通过分析空蚀发生过程中叶片上的压力分布,揭示出离心泵流道内部流场的内在特性,最后对泵的性能进行了预测,说明数值模拟可以为离心泵在特定工况下运行时的空化性能预测提供依据。     

Influence of Cross-Sectional Flow Area of Annular Volute Casing on Transient Characteristics of Ceramic Centrifugal Pump

The annular volute is typically used in a slurry pump to reduce the collisions between solid particles and the volute tongue and to achieve a better resistance to blocking. However, only limited studies regarding annular volutes are available, and there is no systematic design method for annular volutes. In this study, the influence of volute casing cross-sectional flow area on the hydraulic loss, pressure pulsations, and radial force under varying working conditions in a centrifugal ceramic pump are discussed in detail. Experimental tests were conducted to validate the numerical results. The results indicated that, when the volute casing flow area increases, the hydraulic performance decreases marginally under the rated working conditions, but increases at the o-design points, specifically under large flow condition. However, the volute casing with a larger flow area has a wider high-e ciency region. In addition, the increase in the volute casing flow area will decrease the pressure pulsations in the volute, regardless of the working condition, and decrease the radial force on the shaft, therefore, providing an improved pump operational stability. It is anticipated that this study will be of benefit during the design of annular volutes.     

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

The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far.There exist two main problems in the operation of the two-phase flow pumps,i.e.,low overall efficiency and severe abrasion.In this study,the three-dimensional,steady,incompressible,and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics(CFD) code based on the mixture model of the two-phase flow and the RNG k-two-equation turbulence model,in which the influences of rotation and curvature are fully taken into account.The coupling between impeller and volute is implemented by means of the frozen rotor method.The simulation results predicted indicate that the solid phase properties in two-phase flow,especially the concentration,the particle diameter and the density,have strong effects on the hydraulic performance of the pump.Both the pump head and the efficiency are reduced with increasing particle diameter or concentration.However,the effect of particle density on the performance is relatively minor.An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration.The suction side of the blade is subject to much more severe abrasion than the pressure side.The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump,and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.     

螺旋式纸浆离心泵内部流动的数值模拟

为分析螺旋式纸浆离心泵内部流动状态，给优化过流部件结构的优化设计提供基础，采用CFD分析软件Fluent对螺旋式离心泵内部单相流动和固液两相流动进行了数值模拟。给出了螺旋式叶轮建模方法和流场分析方法，分析了泵内流体速度和压力的分布特性，并基于流动模拟结果预测了水力性能，单相输送条件下的计算结果与试验结果取得了较好的一致。通过对一定体积浓度和颗粒粒径下固液两相流的研究计算，分析了螺旋式离心泵叶片表面以及流道内的固液相分布状态，对螺旋式结构的优化具有一定的参考意义。