离心泵失速特性研究

发布时间：2018-04-10 09:41

本文选题：离心泵　切入点：旋转失速　出处：《中国农业大学》2015年博士论文

【摘要】：水泵在小流量工况下运行时,因偏离设计点,叶轮中容易出现失速现象。失速团不断地产生和脱落会诱发压力脉动,使得水泵噪音增强,振动加剧,影响机组安全运行。本文采用大涡模拟方法对离心泵内的失速现象进行了较系统的研究。首先,建立了离心泵失速计算模型。针对离心泵失速流动特征,采用典型SGS模型对离心泵内部流动进行了计算,提出了适合离心泵失速的计算模型,构建了采用动态混合非线性模型(DMNM)求解失速流场的计算策略,为准确分析失速过程奠定了基础。其次,提出了离心泵中失速的表征参数及两种类型失速发生的条件。当叶片数为偶数时,会发生“交替失速”流动现象；当叶片数为奇数时,会发生“旋转失速”流动现象。在出现“交替失速”的前提下,随着叶片数增多,失速团的数量也随之增多,失速涡频率也随之变化；在出现“旋转失速”的前提下,随着叶片数增多,失速团的数量也随之增多,转速变大,失速涡频率也随之增大。第三,利用所建立的离心泵失速计算模型,分析了失速条件下叶轮流动结构及压力脉动特性,给出了两类失速状态下失速团的演变过程及其诱导的压力脉动变化规律。对于“交替失速”,失速团相对叶轮周向未发生旋转,但是失速流道主涡不断摆动,在下游分裂出出口涡。出口涡周期性地增长和脱落,在叶片上所产生的压力脉动表现为中心频率幅值较高的“宽带频率”；随着主涡的衰减,在主涡的上游还会分离成为一个面积较小的涡,并与主涡相互融合,主涡经历“衰减-分裂-融合-壮大”的周而复始过程,在叶片上产生的压力脉动表现出幅值较高的低频。对于“旋转失速”,失速团产生于叶片吸力面头部附近,沿圆周方向向叶片压力面运动,并逐渐衰减；当旋转失速发生以后,叶片上的压力脉动幅值远大于非失速工况,叶片上的压力脉动频率以失速涡频率为主。第四,研究了隔舌区域动静干涉和失速的相互作用,揭示了失速条件下隔舌区压力脉动传播机理。在小流量工况下,当叶轮中发生“交替失速”现象以后,叶轮流道通过隔舌处时会有“固定失速”的流动现象。在“交替失速”初始阶段,隔舌区“固定失速”对压力脉动的影响较弱,“交替失速”的影响占主导；而当流量进一步减小以后,隔舌区“固定失速”对压力脉动的影响占主导,削弱了“交替失速”的作用。而在叶片区压力脉动中,“固定失速”始终占主导,隔舌处强烈的动静干涉作用削弱了旋涡脱落所造成的低频,主要频率为转频及其谐频。本文取得的研究成果,为改善离心泵叶轮设计、提高离心泵在非设计工况下的运行稳定性具有指导意义。
[Abstract]:The impeller is prone to stall because of deviation from the design point when the pump is running under small flow conditions.The constant occurrence and shedding of stall mass will induce pressure pulsation, which will increase the noise and vibration of the pump and affect the safe operation of the unit.In this paper, the stall phenomenon in centrifugal pump is studied systematically by means of large eddy simulation.Firstly, the stall calculation model of centrifugal pump is established.According to the characteristics of stall flow of centrifugal pump, the typical SGS model is used to calculate the flow inside the centrifugal pump, and a calculation model suitable for stall of centrifugal pump is put forward. The calculation strategy of solving stall flow field using dynamic mixed nonlinear model (DMNM) is constructed.It lays a foundation for accurate analysis of stall process.Secondly, the parameters of stall in centrifugal pump and the conditions of two types of stall are proposed.When the number of blades is even, the phenomenon of "alternate stall" flow will occur, and when the number of blades is odd, the phenomenon of "rotational stall" will occur.On the premise of "alternate stall", the number of stall clusters increases with the increase of blade number, and the frequency of stall vortex also changes.The number of stall clusters increases, the rotational speed increases and the stall vortex frequency increases.Thirdly, the flow structure and pressure pulsation characteristics of impeller under stall condition are analyzed by using the established stall calculation model of centrifugal pump. The evolution process of stall mass and its induced pressure fluctuation under two kinds of stall conditions are given.For "alternate stall", the stall group does not rotate relative to the circumference of the impeller, but the main vortex of the stall channel wobbles continuously and splits out the exit vortex downstream.The pressure pulsation of the exit vortex increases and shedding periodically, and the pressure pulsation on the blade is characterized by a "wide band frequency" with higher central frequency amplitude. With the attenuation of the main vortex, it will be separated into a smaller vortex in the upper reaches of the main vortex.The main vortex goes through the process of "attenuation-splitting-fusing-growing", and the pressure pulsation on the blade shows a high amplitude of low frequency.For "rotating stall", the stall mass occurs near the head of the suction surface of the blade and moves toward the blade pressure surface in the circumferential direction, and gradually attenuates. When the rotating stall occurs, the amplitude of the pressure pulsation on the blade is much larger than that on the non-stall condition.The pressure pulsation frequency on the blade is mainly stall vortex frequency.Fourthly, the interaction between static and static interference and stall in tongue septum is studied, and the propagation mechanism of pressure pulsation in tongue septum is revealed.Under the condition of small flow rate, when the phenomenon of "alternate stall" occurs in the impeller, there will be a "fixed stall" when the impeller passage passes through the tongue.In the initial stage of "alternate stall", the effect of "fixed stall" on pressure pulsation in the tongue septum is weak, and the effect of "alternate stall" is dominant, but when the flow rate decreases further,The influence of fixed stall on pressure pulsation is dominant, which weakens the effect of alternate stall.In the pressure pulsation of the blade region, "fixed stall" always dominates. The strong static and static interference at the tongue impairs the low frequency caused by vortex shedding, and the main frequency is rotation frequency and harmonic frequency.The research results obtained in this paper are of guiding significance for improving the design of centrifugal pump impeller and improving the operation stability of centrifugal pump under off-design conditions.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TH311

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