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。     

轴流式水轮机全流道内非定常空化湍流的数值模拟

为了研究轴流式水轮机内部的空化流动,将Fluent 6．1商用软件中的一种完整空化模型和一种混合流体两相流模型相结合,对某水电站原型轴流式水轮机全流道内的非定常空化湍流进行了数值模拟。根据模拟结果,预测了水轮机在特定工况下运行时流道内空化发生的部位和程度,并对水轮机的能量性能进行了预估。数值预测的空化流动现象与模型水轮机空化试验中所观察到的现象基本一致,说明数值模拟结果可为轴流式水轮机的运行性能预测提供参考。     

Numerical investigations on cavitating flows with thermodynamic effects in a diffuser-type centrifugal pump

A cavitation model with thermodynamic effects for cavitating flows in a diffuser-type centrifugal pump is developed based on the bubble two-phase flow model. The proposed cavitation model includes mass, momentum, and energy transportations according to the thermodynamic mechanism of cavitation. Numerical simulations are conducted inside the entire passage of the centrifugal pump by using the proposed cavitation model and the renormalization group-based k-? turbulent model coupled with the energy transportation equation. By using the commercial computational fluid dynamics software FLUENT 6.3, we have shown that the predicted performance characteristics of the pump, as well as the pressure, vapor, and density distributions in the impeller, agree well with that calculated by the full cavitation model. Simulation results show that cavitation initially occurs slightly behind the inlet of the blade suction surface, i.e., the area with maximum vapor concentration and minimum pressure. The predicted temperature field shows that the reduction in temperature restrains the growth of cavitating bubbles. Therefore, the thermodynamic effect should be treated as a necessary factor in cavitation models. Comparison results validate the efficiency and accuracy of the numerical technique in simulating cavitation flows in centrifugal pumps.     

高功率密度液力变矩器空化特性研究

高功率密度液力变矩器由于其内部流速高、局部压力低而易出现空化现象,导致其液力性能恶化。针对液力变矩器内空化现象进行试验及数值研究,通过对不同转速、不同速比及不同补偿油压力下液力变矩器性能测试,获得空化随工况及供油条件变化规律。构建基于Rayleigh-Plesset的全流道瞬态空化仿真模型对不同工况下液力变矩器内部两相空化流动进行预测,利用应力混合涡模拟湍流模型精确捕捉涡流状态,实现对有/无空化下液力变矩器内部流场及液力特性的计算。结果表明,液力变矩器在高泵轮转速、低速比及低补偿压力下容易发生空化,空化程度随着速比的下降而升高,在起动工况时达到最大。在空化工况下,液力变矩器导轮流道内产生大量空泡,空泡阻碍油液流动,导致循环流量降低,进而使液力变矩器传递功率的能力下降,起动工况下能容系数降低高达31%。全流道瞬态空化模型能够实现液力变矩器空化特性的精确预测,对变矩比、能容系数及效率的最大预测误差由无空化的30%降低至5%。     

旋流泵内盐析两相流场的计算及试验研究

为研究流体机械内部伴有盐析的液固两相流动情况,自行设计了旋流式模型泵,采用双流体模型计算了该泵在最优工况下的氯化钠盐析两相流场,并采用先进的激光相位多普勒粒子测速仪测量了泵无叶腔及叶轮内部盐析两相流的三维速度场。将试验结果与计算结果进行对比,验证了计算模型的适用性,并给出了误差分析。通过对试验测得的周向、轴向、径向速度及其对应的脉动速度分布曲线讨论,初步揭示了该型泵内盐析两相流动特征。在整个流道内,盐析晶体颗粒大部分集中于无叶腔,且分布较均匀;进入叶轮后向叶片工作面靠拢;颗粒浓度最低处是在叶轮进口叶片背面靠近叶轮后盖板附近;液固两相在叶轮与无叶腔中的周向速度分布差异明显;两相间速度及脉动速度有滑移,但差异总体上并不显著。     

挖泥泵数值仿真与实测比较

通过求解包括进水管、叶轮、泵体等过流部件在内的水泵流道内的三维稳定雷诺平均Navier-Stokes方程,获得水泵内部的流场分布特征。对计算结果与实测结果进行了对比。表明计算所得流量-扬程曲线与实测值吻合良好;流量．效率曲线在小流量相差较大,在大流量吻合得较好。虽然在部分运行工况模拟计算不是很准确,但计算的各工况压力、速度分布以及整个流道的其它流动特性,对分析挖泥泵的各种流动问题很有帮助。     

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。     

混流式喷水推进器空化性能数值分析

基于RANS方程,结合切应力输运湍流模型计算某混流式喷水推进器无空化状态时的流体动力性能。与厂商提供的数据对比表明,建立的数值模型和计算方法是可信的。在此基础上,嵌入基于Rayleigh-Plesset方程的混合物均相流空化模型,对空化条件时该喷水推进器流体动力性能进行数值计算与分析。计算得到的功率、推力等宏观量与厂商提供的数据吻合较好。计算得到空化发生时的临界进口速比值。计算结果表明,喷水推进器叶轮发生空化时,泵的流量、扬程明显降低,进而引起推力下降;在等功率条件下,随着进口速比的降低,喷水推进器叶轮空化程度越来越严重;进水流道空化的发生较喷泵叶轮空化滞后,喷口部分仅产生空间空化,较叶轮空化提前,而固壁上不产生空化;数值计算结果还证明空化限制线即为等汽蚀比转速线,且空化限制线1、2、3对应的汽蚀比转速分别约为1 280、1 390和1 580。     

两相流离心泵水力输送性能计算分析

为探索一台固液两相流离心泵的水力性能与磨损特性,基于代数滑移混合物模型(Algebraic slip mixture model,ASMM)对其内部流场进行三维不可压缩定常流动数值计算,其中转子与定子之间的动静耦合采用"冻结转子法"实现。多相位定常流动计算结果与水力试验结果的对比确定最佳的转动位置,并确认数值计算方法的准确性。预测结果表明,颗粒属性对模型泵水力性能影响的次序为固相体积分数、颗粒密度和粒径。随着颗粒直径、密度和固相体积分数的增加,预测扬程均下降;效率总体上也呈现下降趋势,但在固相体积分数为10%时输送效率最高。在靠近隔舌的叶轮出口处存在由低、中、高三种速度组合的双剪切层射流—尾流结构。总体而言,模型泵叶片吸力面的磨损程度比压力面更为严重。固相体积分数对叶片表面磨损程度的影响比较明显,颗粒密度影响较小,颗粒直径仅对吸力面磨损程度影响显著,对压力面影响不明显。     

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.     

叶片进口修缘对离心泵汽蚀性能影响的数值计算与试验研究

为了改善离心泵的汽蚀性能,根据经验,确定了两种叶片进口修缘形式。首先通过原型泵的外特性试验,确定了能量性能和汽蚀性能曲线。基于完整空化模型和混合流体两相流模型,对原型泵运行工况下叶轮内空化流动进行全流道数值计算。预测得到原型泵能量性能和汽蚀性能曲线,与试验曲线吻合良好;同时得到汽蚀发生过程中叶轮流道内空化发展的静态特征,与理论相符。故采用相同的数值分析方法对两种叶片进口修缘后的叶轮进行分析,分析表明：进口修缘后泵的汽蚀性能得到了提高,叶片进口工作面修缘形状越接近流线型,泵的汽蚀性能越好。对较好修缘形式的泵进行试验,得到其能量性能曲线和汽蚀性能曲线,数值分析与试验研究的曲线吻合,修缘后泵的临界汽蚀余量得到改善。研究结果对离心泵汽蚀改善的方法具有一定的指导意义。     

离心泵蜗壳内非定常流动特性的数值模拟及分析

基于RNG k-ε湍流模型和Zwart-Gerber-Belamri空化模型,对离心泵内部非空化和空化工况下的非定常流动特性进行数值模拟,分析空化模型中凝结项经验系数对数值模拟结果的影响,并根据试验结果修正离心泵空化流动数值模拟中凝结项经验系数;数值模拟得到的离心泵扬程随有效空化余量的变化曲线与试验结果吻合较好,验证数值计算模型和方法的准确性和可靠性。数值模拟结果表明：离心泵非定常流动中,非空化、临界空化和充分发展空化工况下,蜗壳内监测点的压力脉动主频均为叶片通过频率;空化对离心泵蜗壳内压力脉动的影响较大,非空化时压力脉动最大幅值在蜗舌处,空化时压力脉动最大幅值在第1断面附近,其原因是离心泵出现空化时第1断面处旋涡强度增强,且随时间变化剧烈,对流动产生强烈扰动。     

泵空化流数值计算研究现状及展望

空化是一种包含气液相间质量传输的非定常可压缩多相湍流流动现象,它是泵性能和效率下降的主要原因。空化流动的计算主要涉及空化模型和湍流模型两个方面。本文概述了空化模型的一些基本理论,并比较了各个空化模型的优缺点;简要分析了湍流模型对空化流计算的影响;介绍了这些模型在泵空化流计算中的应用;最后展望了泵空化流计算模型的发展方向。     

Numerical investigation of suction vortices behavior in centrifugal pump

A numerical simulation on suction vortices behavior in a centrifugal pump was carried out to investigate their influence on the internal flow through impellers including formation and shedding of cavitation by using a finite-volume method and k-ω Shear Stress Transport turbulence model. For cavitating flow, a two phase homogeneous cavitation model was used. A full three-dimensional flow in a single-section centrifugal pump consisting of a six blade impeller and shroud ring was computed with structured mesh. A constant suction vortex is imposed as a boundary condition. Vortices behavior was investigated according to the variation of flow rates of two pump systems with and without suction vortices. From the results, suction vortices induced biased flow structure and more cavitations, especially at the low flow rate condition. Complicated internal flow phenomena through impellers such as formation of cavitations, growing and shedding of the vortex, flow separation and flow unsteadiness due to the suction vortices are investigated and discussed.     

Assessment of a turbulence model for numerical predictions of sheet-cavitating flows in centrifugal pumps?

Various approaches have been developed for numerical predictions of unsteady cavitating turbulent flows. To verify the influence of a turbulence model on the simulation of unsteady attached sheet-cavitating flows in centrifugal pumps, two modified RNG k-? models (DCM and FBM) are implemented in ANSYS-CFX 13.0 by second development technology, so as to compare three widespread turbulence models in the same platform. The simulation has been executed and compared to experimental results for three different flow coefficients. For four operating conditions, qualitative comparisons are carried out between experimental and numerical cavitation patterns, which are visualized by a high-speed camera and depicted as isosurfaces of vapor volume fraction α _v = 0.1, respectively. The comparison results indicate that, for the development of the sheet attached cavities on the suction side of the impeller blades, the numerical results with different turbulence models are very close to each other and overestimate the experiment ones slightly. However, compared to the cavitation performance experimental curves, the numerical results have obvious difference: the prediction precision with the FBM is higher than the other two turbulence models. In addition, the loading distributions around the blade section at midspan are analyzed in detail. The research results suggest that, for numerical prediction of cavitating flows in centrifugal pumps, the turbulence model has little influence on the development of cavitation bubbles, but the advanced turbulence model can significantly improve the prediction precision of head coefficients and critical cavitation numbers.     

蜗壳形状对高速部分流泵性能的影响

利用FLUENT6.3.21软件,选择了S-A湍流模型,对同一叶轮配两种蜗壳的高速部分流泵进行了内部流场数值模拟和性能预测,通过比较分析,提出采用矩形螺旋蜗壳能提高关死点扬程,得到较为平坦的扬程曲线,且能提高泵的效率.并通过内部流场分析,解释了引起外特性差异的原因.     

Numerical simulation and analysis of flow characteristics in the front chamber of a centrifugal pump

We performed numerical simulations to study the flow characteristic in a centrifugal pump based on the RANS equations and the RNG k-ε turbulent model. The flow field, including the front and back pump chambers, the impeller wear-ring, the impeller passage, the volute casing, the inlet section and outlet section was calculated to obtain accurate numerical results of fluid flow in a centrifugal pump. The flow characteristic was studied from the internal flow structure in pump chambers, the radial velocity at impeller outlet as well as the pressure inside of the pump, the circumferential velocity and the radial velocity in front pump chamber. The variation of flow parameters in internal flow versus flow rate in the centrifugal pump was analyzed. The results show that the overall performance of the pump is in good agreement with the experimental data. The simulation results show that the distribution of flow field in the front pump chamber is axial asymmetry. The energy dissipation at the impeller outlet is larger than other areas. The distribution of the circumferential velocity and that of radial velocity are similar along the axial direction in the front pump chamber, but the distribution of flow is different along the circumferential and the radial directions. It was also found that the vorticity is large at the impeller inlet compared with other areas.     

Numerical and experimental investigation of cavitation flows in a multistage centrifugal pump

Cavitation behavior is very important in pumps for long time operation. However, there is difficulty in predicting the cavitation phenomena of pumps by Computational fluid dynamics (CFD). In order to accurately ascertain cavitation behavior, a comparison between CFD and experimental data is a significant and essential process. The purpose of this study is to analyze cavitating behavior in multistage centrifugal pumps numerically and experimentally. For this investigation an experimental set up was used to obtain cavitation performance results. The CFD method was used to investigate the multistage centrifugal pump performance under developed cavitating conditions. The Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was adopted to account for turbulent flows. Numerical data were validated with experimental data and a good comparison of results was achieved. Numerically, cavitation performances were obtained for different pump stages and the effects on cavitation were described according to different NPSH (Net positive suction head). The occurrence of cavitation was also described according to NPSH3% in the head drop lines and water vapor volume fraction on the impeller blade. The rapid drop in head at low NPSH was captured for different flow conditions. It was found that for stage to stage performance, the head drop changes could be related to losses inside the pump. It was also shown that the simulation results can truly represent the development of the attached sheet cavitation in the impeller.     

Effects of Blade Number on Characteristics of Centrifugal Pumps

The blade number of impeller is an important design parameter of pumps,which affects the characteristics of pump heavily.At present,the investigation focuses mostly on the performance characteristics of axis flow pumps,the influence of blade number on inner flow filed and characteristics of centrifugal pump has not been understood completely.Therefore,the methods of numerical simulation and experimental verification are used to investigate the effects of blade number on flow field and characteristics of a centrifugal pump.The model pump has a design specific speed of 92.7 and an impeller with 5 blades.The blade number is varied to 4,6,7 with the casing and other geometric parameters keep constant.The inner flow fields and characteristics of the centrifugal pumps with different blade number are simulated and predicted in non-cavitation and cavitation conditions by using commercial code FLUENT.The impellers with different blade number are made by using rapid prototyping,and their characteristics are tested in an open loop.The comparison between prediction values and experimental results indicates that the prediction results are satisfied.The maximum discrepancy of prediction results for head,efficiency and required net positive suction head are 4.83%,3.9% and 0.36 m,respectively.The flow analysis displays that blade number change has an important effect on the area of low pressure region behind the blade inlet and jet-wake structure in impellers.With the increase of blade number,the head of the model pumps increases too,the variable regulation of efficiency and cavitation characteristics are complicated,but there are optimum values of blade number for each one.The research results are helpful for hydraulic design of centrifugal pump.     

超低比转速复合式离心泵内部流动特性分析

为研究超低比转速复合式离心泵内部流动特性,以一台比转速为16、半开式复合叶轮离心泵为研究对象,应用ANSYS-Fluent19R1软件对模型泵进行三维全流场数值模拟计算,得出泵内部流场及作用在叶轮、蜗壳上的径向力分布规律。结果表明:在不同流量工况下,随着流量的增加,在隔舌附近出现较大的压力梯度;在长叶片与短叶片相间隔流道内低速区面积较大、叶轮出口处分布较多的旋涡;当流量从0.2倍增加至1.8倍额定流量时,作用在蜗壳上的径向力幅值逐渐减小,作用在叶轮上的径向力幅值先减小后增加,在1.0倍额定流量时径向力幅值达到最小,而后增大。为超低比转速复合式离心泵的设计优化提供参考。