Cavitation mode analysis of pump inducer

The onset of cavitation causes head and efficiency of a main pump to be reduced significantly and generates vibration and noise. In order to avoid these phenomena, the inlet of the pump is fitted with a special rotor called an inducer, which can operate satisfactorily with extensive cavitation. The motivation of this study is to find out cavitation modes from the inducer inlet pressure signals and event characteristics from outlet ones at various operating conditions. The cavitation modes are analyzed by using a cross-spectral density of fluctuating pressures at the inducer inlet. The time-frequency characteristics of wall pressures downstream of the inducer are presented in terms of event frequency, its duration time, and number of events by using the Choi-Williams distribution.     

Experiments on cavitation instability of a two-bladed turbopump inducer

The turbopump is a pressurizing system that supplies liquid propellants to the combustion chamber of a rocket engine at high pressure. As an integral component of a high-speed pumping system, the inducer used in a turbopump is forward-attached to an impeller to improve suction performance. This paper describes an experimental investigation on the flow instabilities of a two-bladed axial inducer due to cavitation. Cavitation development and its instabilities were analyzed. Asymmetric cavitation and cavitation surge were observed, and characterized by measuring the inlet pressure fluctuation for various cavitation numbers and flow coefficients. As flow coefficient decreases, the increased intensity of asymmetric cavitation was observed with an increased inception number of asymmetric cavitation. The frequency of the detected cavitation surge in the 4–10Hz range varied depending on the cavitation number. The instantaneous transition to cavitation surge appeared at the end of asymmetric cavitation as the cavitation number decreased. However, a further decrease in cavitation number resulted in the stable operation of the inducer with low values of pressure fluctuation. Finally, an intensive cavitation surge appeared after a significant amount of head loss.     

双向轴流泵装置性能预测与内部流动分析

对一采用S形叶片的双向轴流泵装置进行数值研究,在不同流量工况条件下分析泵的正、反向运转性能,对该泵的瞬时启动过程进行了监测并对泵内的非定常空化现象进行了分析。研究表明,正、反向运转时,泵的性能存在明显的差异,反向的扬程和效率均高于正向;在泵正向启动过程中,叶轮背面进口边产生空化区,反向运转时未发生明显的空化现象;两种运转模式下,叶轮进出口断面上压力脉动特征频率分布相似,但叶轮进口的压力脉动幅值较高。     

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.

     

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.     

Experimental study on hydrodynamic performance of a cavitating centrifugal pump during transient operation

An experimental study has been carried out in order to analyze the cavitation of a centrifugal pump and its effect on transient hydrodynamic performance during transient operation. The transient characteristics of the centrifugal pump were tested under various suction pressure and starting conditions. In transient operation of continuous starting and stopping process, instantaneous rotational speed, head, flow rate and suction pressure of the pump were measured. The effect of cavitation on transient performance of the centrifugal pump during transient operation was analyzed, and then the effects of starting acceleration rate and suction pressure of pump on cavitation were presented. Results showed that the cavitation would be delayed during rapid starting period. However, in the condition of low suction pressure and high rotational speed, pump cavitation is inescapable even if the starting period is less than a second. After the serious transient cavitation occurred, the transient performance of centrifugal pump would decline obviously, and the instantaneous head of pump would fluctuate.     

Experimental analysis of flow fields inside intake heads of a vacuum cleaner

The flow structure inside the intake head greatly affects the working efficiency of a vacuum cleaner such as suction power and aero-acoustic noise In this study, the flow inside intake heads of a vacuum cleaner was investigated using qualitative flow visualization and quantitative PIV (Particle Image Velocimetry) techniques The aerodynamic power, suction efficiency and noise level of the intake heads were also measured In order to improve the performance of the vacuum cleaner, inner structure of the flow paths of the intake head, such as trench height and shape of connection chamber were modified. The flow structures of modified intake heads were compared with that of the original intake head The aero-acoustic noise caused by flow separation was reduced and the suction efficiency was also changed due to flow path modification of intake head In this paper, the variations of flow fields for different intake heads are presented and discussed together with results of aerodynamic power, suction efficiency and noise level     

Experimental study of the influence of flow passage subtle variation on mixed-flow pump performance

In the mixed-flow pump design, the shape of the flow passage can directly affect the flow capacity and the internal flow, thus influencing hydraulic performance, cavitation performance and operation stability of the mixed-flow pump. However, there is currently a lack of experimental research on the influence mechanism. Therefore, in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance, the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment. In this experiment, parameters, such as the head, the efficiency, and the shaft power, are measured, and the pressure fluctuation and the noise signal are also collected. The research results suggest that after processing the inlet flow passage, the head of the mixed-flow pump significantly goes down; the best efficiency of the mixed-flow pump drops by approximately 1.5%, the efficiency decreases more significantly under the large flow rate; the shaft power slightly increases under the large flow rate, slightly decreases under the small flow rate. In addition, the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump. At the same time, the noise dramatically increases. Overall speaking, the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance, thus suggesting a special attention to the optimization of flow passage. This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment, which will benefit the optimal design of the flow passage of the mixed-flow pump.     

Comparison of cavitation prediction for a centrifugal pump with or without volute casing

Cavitation may not only cause head and efficiency breakdown of hydraulic machines but also generate other unfavorable phenomena such as noise and vibration. Therefore, the accurate prediction of cavitation development is important for various pump applications. In this paper, two numerical models, namely, models A and B, are applied to simulate the turbulent cavitating flows inside a centrifugal pump to investigate the effect of calculation domain on the prediction accuracy of cavitation performance for hydraulic machines. Model A has a calculation domain with volute casing, whereas model B has a single blade-to-blade flow passage without volute casing. Steady simulations of cavitating flow in the pump have been conducted based on the shear stress transport k-ω turbulence model and the homogeneous cavitation model. Both models A and B predicted that the pump performance decreases with decreasing cavitation number. Experimental results show that model B can predict better the critical cavitation number at the best efficiency point compared with model A, which is the full flow passage model. Internal flow investigations indicate that an asymmetrical feature of cavitating flow exists when the calculation domain with volute casing is applied. The asymmetrical cavitation development in different blade-to-blade flow passages for model A results in an over-estimation of the decrease in pump performance because of the interaction between the impeller blade and the tongue of the volute casing. A simple calculation domain without volute casing is preferred for steady cavitation prediction in pumps rather than the full flow passage with volute casing because the former has better convergence, less resource requirements, and lower time consumption.     

轴向柱塞泵低气压运行特性建模与试验分析

空化是影响液压系统动态特性的重要因素,为此开展了轴向柱塞泵低压环境下的工况研究。考虑气液两相混合油液的密度、体积弹性模量和黏度的影响,限制入口油腔的最低压力,建立轴向柱塞泵的压力流量模型,计算获得轴向柱塞泵在不同工况下的流量特性,并通过试验验证。研究表明:负载增大导致更严重的空化以及泄漏,并使容积效率降低;轴向柱塞泵在达到临界流量之后,转速提升只会加剧空化,而不能提升流量;最大容积效率出现在临界流量产生之前。为轴向柱塞泵低气压性能预测提供了理论支撑。     

低汽蚀余量磁力泵的试验研究

为了获得良好的抗汽蚀性能,对磁力泵叶轮采取低汽蚀余量设计措施,同时配置变螺距诱导轮.在结构上利用永磁传动实现了无泄漏,解决了转子体轴向力平衡、导轴承结构与材料、循环回路润滑冷却等重要技术问题.经样机的试验检测表明,低汽蚀余量磁力泵的流量、扬程和必须汽蚀余量性能及其振动值均达到了设计要求.     

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。     

往复泵水头损失及空化现象的数值仿真优化

为减轻往复泵的水头损失及空化现象，以提高吸入性能，根据魏斯特法尔理论分析了泵阀运动特性，基于阀盘结构和活塞冲次等参量，提出了水头损失和空化量的优化模型。采用Fluent动网格技术进行动态数值模拟，分析了各参量对吸入过程水头损失和空化现象的影响及其发展过程，优选出了最佳阀盘结构参数和活塞冲次，可有效减小液缸内的水头损失，降低因阀盘开启滞后而产生的空化现象，改善泵的吸入性能和汽蚀现象。得出了往复泵吸入过程水头损失最小、活塞端面的空化量最小时的阀盘锥角及最优的工作冲次，为往复泵的吸入特性研究提供了参考依据。     

Cavitation optimization for a centrifugal pump impeller by using orthogonal design of experiment

Cavitation is one of the most important performance of centrifugal pumps. However, the current optimization works of centrifugal pump are mostly focusing on hydraulic efficiency only, which may result in poor cavitation performance. Therefore, it is necessary to find an appropriate solution to improve cavitation performance with acceptable efficiency. In this paper, to improve the cavitation performance of a centrifugal pump with a vaned diffuser, the influence of impeller geometric parameters on the cavitation of the pump is investigated using the orthogonal design of experiment(DOE) based on computational fluid dynamics. The impeller inlet diameter D_1, inlet incidence angle Δβ, and blade wrap angle φ are selected as the main impeller geometric parameters and the orthogonal experiment of L_9(3*3) is performed. Three-dimensional steady simulations for cavitation are conducted by using constant gas mass fraction model with second-order upwind, and the predicated cavitation performance is validated by laboratory experiment. The optimization results are obtained by the range analysis method to improve cavitation performance without obvious decreasing the efficiency of the centrifugal pump. The internal flow of the pump is analyzed in order to identify the flow behavior that can affect cavitation performance. The results show that D_1 has the greatest influence on the pump cavitation and the final optimized impeller provides better flow distribution at blade leading edge. The final optimized impeller accomplishes better cavitation and hydraulic performance and the NPSHR decreases by 0.63 m compared with the original one. The presented work supplies a feasible route in engineering practice to optimize a centrifugal pump impeller for better cavitation performance.     

对转轴流泵的设计与数值分析

对转轴流泵是由2个叶轮串联在一起,以相反的方向绕同一轴心旋转的轴流泵.与常规前、后导叶式轴流泵相比,在同样设计参数条件下,对转式轴流泵具有相对体积小、运转速度低、抗空化性能好和推重比高等特点.为探究对转轴流泵的设计理论和方法,设计了一对转轴流泵的前、后置叶轮,应用Matlab软件实现参数化设计,搭建了自动分析优化平台,...     

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。     

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 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.     

角度变化系数对变螺距诱导轮性能的影响

在变螺距诱导轮设计过程中引入角度变化系数来控制型线变化的规律,利用自主开发的诱导轮设计软件,选取代表3种不同特征型线的角度变化系数,设计了3台不同型线变化规律的变螺距诱导轮,并通过数值计算的方法,研究了角度变化系数m对诱导轮性能的影响。结果表明,诱导轮的扬程与效率随着角度变化系数的增加逐渐降低,在m=0.5时诱导轮的扬程与效率最高;诱导轮的临界空化余量随着角度变化系数的增加而逐渐降低,在m=2时诱导轮的空化性能最优。因此,在进行诱导轮的角度变化系数选择时,要综合考虑诱导轮的能量特性和空化特性。