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。     

等螺距诱导轮内部流动的数值模拟

基于雷诺时均N-S方程和S-A湍流模型对等螺距诱导轮内部的流动进行三维紊流数值计算和分析,获得诱导轮流道内的速度场、压力场的分布规律。发现诱导轮最易发生汽蚀破坏的位置在叶片吸力面进口前缘的外缘处,相对速度的大小从轮毂到轮缘大致上是沿径向增加的,从轮毂到半径的中部相对速度的增加的幅度大于从半径中间到轮缘的增长幅度;静压从诱导轮进口到叶片尾部是增加的,但从叶片尾部到诱导轮的出口的部分区域静压会减少。并针对有和无诱导轮两种情况,对高速离心泵进行试验研究,通过试验验证了具有前置诱导轮的离心泵可以改善泵的汽蚀性能。所提出的诱导轮模拟方法对高速诱导轮离心泵的进一步研制和优化设计具有一定的指导意义。     

诱导轮叶片参数对大流量离心泵汽蚀性能的影响

诱导轮作为离心泵的重要辅助部件之一,对水泵汽蚀性能的改善有重要作用。针对某大流量离心泵汽蚀性能不佳的问题,采用响应面分析和数值模拟的方式,对该离心泵的诱导轮叶片参数进行了优化,探究了诱导轮导程、叶片厚度和叶片数对大流量离心泵汽蚀性能的影响规律。首先,构建了大流量离心泵的仿真模型,对其进行了外特性计算,将计算结果与试验结果进行了对比,对仿真结果的可靠性进行了验证;然后,根据诱导轮扬程与泵汽蚀性能呈正相关的规律,以诱导轮的叶片参数(导程L、厚度T、叶片数Z)为变量因素,以诱导轮扬程最大为优化目标,对诱导轮进行了响应面计算分析,得到了响应面优化后的诱导轮叶片参数,并对比分析了优化前后诱导轮的扬程;最后,针对诱导轮优化前后的离心泵,在不同工况下进行了叶轮汽蚀情况和临界汽蚀余量对比分析。研究结果表明：叶片导程对诱导轮扬程的影响不大,而减小叶片厚度、增加叶片数可以大幅提高诱导轮扬程;额定工况下,经响应面优化后的诱导轮扬程提高了0.6 m,泵的临界汽蚀余量相比原型泵降低了0.15 m。该结果可以为大流量离心泵诱导轮的优化设计提供理论参考。     

高速诱导轮三维空化内流场计算

采用三维CFD模拟技术对一个高速涡轮泵诱导轮中的空化流动进行了研究。计算准确预测出叶片和横截面上的静压和速度分布，并得到诱导轮的扬程性能；对不同流量下的蒸气相体积份额进行了比较；流线图表明回流涡造成进口低压区，会引起空化的产生；同时还显示并分析了诱导轮中空化区与内部流动的关系。     

等螺距诱导轮的理论分析与数值模拟

基于N-S方程,利用Ansys cfx软件对离心泵诱导轮内部流场进行了全三维湍流数值模拟,获得诱导轮内部的速度分布、静压分布,分析了轮缘处叶片压力面和吸力面存在压差引起涡流,进口低压区对诱导轮汽蚀性能的影响,模拟结果为诱导轮的改进设计提供了一定的理论依据。     

诱导轮出口螺距对离心泵空化性能的影响

为了查明诱导轮出口螺距对离心泵空化性能的影响,设计了入口螺距相同、出口螺距逐渐增大的三个诱导轮:诱导轮5-5、诱导轮5-8、诱导轮5-11;采用k-ε湍流模型和Singhal空泡动力学模型,对泵内流动进行空化数值模拟,分析了设计工况下离心泵空化断裂特性和气泡分布流场特征。结果表明:相比于等螺距诱导轮5-5,加设变螺距诱导轮5-8及5-11的离心泵在相同进口压力条件下具有更高的扬程和更少的流场内气泡分布,在同一流量工况下具有更低的空化断裂点,在空化断裂点泵扬程分别提高了10.4%和18.6%;变螺距诱导轮保持进口螺距不变,增大出口螺距可以进一步提升半开式叶轮离心泵抗空化性能。     

永磁超环面传动行星轮轮齿空间磁场分布计算

以磁场理论为基础,对永磁超环面传动行星轮轮齿的空间磁场分布进行了分析计算,推导出了永磁超环面传动行星轮轮齿磁场分布的计算公式,利用所得公式对永磁超环面传动行星轮轮齿磁场在轮齿轴线及各轴截面上的分布进行了计算,分析总结了永磁超环面传动行星轮轮齿磁场空间分布的影响因素及分布规律,结果为进一步研究永磁超环面传动输出转矩的计算提供了理论基础.     

诱导轮叶片开缝对高速离心泵空化性能的影响

为研究诱导轮叶片表面开缝对高速离心泵空化性能的影响规律,设计叶片开缝系数k为0(叶片未开缝)、6.7%、13.3%、20%和26.7%五种叶片开缝方案。基于RNG k-ε湍流模型和Reyleigh-plesset空化模型对高速离心泵进行全流道三维数值模拟,对比分析了诱导轮截面内流线和压力分布规律、诱导轮内空泡发展过程及离心泵的空化特性曲线。研究结果表明诱导轮叶片入口轮缘处开缝可减小亦或是消除该区域的低压区,且对离心泵的水力性能的影响较小;缝隙可抑制并减小初生空化阶段空泡体积分布;开缝系数k对高速离心泵空化性能的影响存在最优值,该研究中开缝系数k=13.3%时,诱导轮的空化性能表现最优。     

UG/Grip技术在诱导轮三维设计中的运用

运用UG/Grip技术对诱导轮进行三维造型设计,获得了一种先进的诱导轮参数化设计方法.同时可采用交互方式对诱导轮设计参数进行修改,增强了诱导轮计算机辅助设计系统的交互设计能力,对提高诱导轮设计质量具有重要意义.     

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。     

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.     

变螺距诱导轮的设计步骤及参数选择

详细介绍了变螺距诱导轮的设计过程，给出了其主要结构参数的计算方法或选择依据，对诱导轮与离心轮的结构匹配关系进行了探讨。通过实例验证，文中提出的设计方法设计的诱导轮具有很好的汽蚀性能。     

Effect of the flat tank bottom on performance and cavitation characteristics of a cargo pump

A submerged cargo pump is installed vertically above the bottom of a cargo tank. The intake shape of the pump is an important operation parameter. Therefore, we investigated the performance and cavitation characteristics of the cargo pump with intake according to intake shape. A cargo pump was composed of an intake, inducer, impeller, and diffuser. First, a cargo pump with a straight pipe intake was measured. Next, the cargo pump with an intake applied the tank bottom shape was investigated. The results of performance and efficiency were compared. The flow characteristics in the inducer changed as the flow passed through the intake affected by the tank bottom shape. The pump head and the efficiency slightly decreased, but the inducer head considerably reduced. Since the incidence angle became a negative value and the cavity volume increased at the leading edge of inducer, the NPSHr (Required net positive suction head) increased. As the inlet pressure decreased, cavitation instabilities clearly appeared. Different gaps between the pump intake and the tank bottom were also investigated. The gap had a critical point without the significant performance loss decrease.     

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.

     

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.     

小流量高扬程离心旋涡泵的设计与试验研究

采用加大流量法对小流量高扬程离心旋涡泵进行了水力设计,并对自行研制的HTB-5/60型离心旋涡泵进行了与开式旋涡叶轮、复合离心叶轮及诱导轮有关的性能试验及汽蚀试验.试验研究表明:设计的诱导轮大大提高了泵的汽蚀性能,样泵的各项性能均可达到设计要求,复合离心叶轮与开式旋涡叶轮串联离心旋涡泵的理论设计是可行的.