叶片出口角对化工流程泵流动及结构动力特性的影响

发布时间：2018-01-24 18:31

本文关键词： 高比转数离心泵叶片出口角非定常流动结构动力特性流固耦合　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：高比转数离心泵是指比转数为150~300的离心泵,多应用于航天工程、电力工程、化学化工等领域。本文针对某一型号高比转数化工流程离心泵的设计优化展开相关研究工作,并得到校创新人才协同培养项目(XTPY201618)的资助。化工流程泵是化工生产装置中的重要基础设施,也是使用量最大的旋转机械,在化工流程中起着关键性作用。近年来,随着社会经济发展,型式单一、运行稳定性差、耗能高的化工流程泵已经满足不了未来工业4.0的要求。离心泵的运行效率很大程度上由关键过流部件尤其是叶轮水力设计决定的,而目前针对研究叶片主要几何参数对泵内部流动特性及结构动力特性的影响规律研究还不够全面和深入。某公司从经济效益最大化出发,要求在不改变主体结构的前提下仅对叶片重新设计优化以提高水力效率。因此,本文着眼于叶片出口角这一关键参数,从其对外特性、内流场以及结构动力特性等多方面特征来揭示其影响规律和机理。本文主要的研究内容及创新点有:1.以一台高比转数化工流程离心泵为研究对象,在原型泵的基础上保证其他几何参数不变,设计了4个叶片出口角(17°、27°、37°、47°)的叶轮方案,并对不同方案进行了多工况下的非定常数值模拟。通过外特性对比分析,可以发现:随着叶片出口角的增大,额定工况下扬程增加,这是由于出口圆周速度随叶片出口角的增大而增大,结合泵基本方程,不难发现扬程随出口圆周速度的增大而增大,但如果叶片出口角过大,则会导致叶片弯曲严重,出现“S”形,流道明显变短,相邻叶片间的扩散角变大,导致水力损失增大,效率也会明显下降,尤其是在大流量工况下表现更明显。将原型泵重复性较好的外特性试验数据与数值模拟预测值对比,可以验证研究中流体域模型构建正确,数值模拟方法可靠。2.为了更明显地呈现对比分析结果,从而能更直观地掌握叶片出口角对化工流泵内部流动特性的影响,仅针对新设计的4个叶轮模型进行内部非定常流动特性分析,通过分析叶轮中截面上的静压分布,湍动能与速度矢量分布,正则化螺旋度分布以及小流量工况下叶轮轴面上的回流特性,以揭示叶片出口角在不同工况下对内部流动特性的影响规律。研究表明:随着叶片出口角增大,叶轮进口的低压流体区域逐渐向出口方向扩散,在叶片工作面附近存在逆压梯度并有不稳定的低压流体聚集,容易发生流动分离;叶片出口角过大时,湍动能整体偏大,所带来的轴向漩涡有所扩大,尤其是对大流量工况而言,近乎扩大到整个流道;小流量工况下的正则化螺旋度最大,意味着流动容易失稳,从而会产生不稳定流动结构,回流现象随叶片出口角的增大而有所加剧,并且主要是在靠近前后盖板面上发生回流,这个现象和正则化螺旋度预测的失稳特征相吻合;叶片出口角为47°的叶轮中截面上的螺旋度分布出现紊乱现象,同时,既有正向漩涡也有逆向漩涡产生,且强度较大,这可能是由于叶片出口角增大导致叶轮扫掠的尾迹区有所增大引起的。3.对比分析4个方案多工况下的压力脉动以及叶轮所受径向力分布,以揭示叶片出口角对泵内部非定常流动特性的影响规律。研究结果表明:在1.0Q工况下,压力脉动幅度随叶片出口角增大而增大,但脉动主频没有发生变化,说明产生压力脉动的主要因素还是叶片与隔舌的动静干涉作用;大流量工况下的压力脉动明显比小流量工况下的要剧烈,且幅值普遍较大;随着叶片出口角增大,次主频有向低频处移动的趋势,说明叶片出口角对流动结构有影响,从而对压力造成了一定影响。对4个方案在不同工况下计算叶轮所受径向力分析可知:叶轮所受径向力均是在额定工况下受力最小;叶片出口角对小流量工况下的径向力分布影响最大;一定程度上减小叶片出口角能够有效改善作用在叶轮上的径向力分布。4.为全面揭示叶片出口角对泵结构动力特性的影响规律,首次基于双向流固耦合作用下对各方案进行额定工况下的数值计算。对比分析了流固耦合作用前后预测的扬程值,可以发现流固耦合作用下预测值比非流固耦合作用下预测值低,但模拟误差明显减小了;对比分析交界线的等效应力分布,结果表明:叶片出口角对叶片背面与前后盖板交界线上的等效应力分布影响不大,而对叶片工作面与前盖板交界线在0.6倍出口到0.8倍出口位置以及叶片工作面与后盖板交界线在0.8倍出口到出口位置影响很大,并且等效应力会随叶片出口角的增大而增大;此外还发现在出口附近均出现了应力集中现象;对比分析额定工况下4个叶轮的计算变形量可以发现:适当减少叶片出口角有助于减少变形量,改善叶轮变形分布情况;对比分析叶轮最大等效应力,表明:叶片出口角过大,会导致最大等效应力偏大,过小则会带来较大幅度的交替动载荷;流固耦合作用下的叶轮结构动力特性研究表明:4个方案下的叶轮第一阶固有频率远大于1倍叶频,同时也避开了二次谐波和三次谐波频率,叶片出口角选取较大时,有助于提高固有频率,但过大则会导致振型较大幅度的摆动和扭动,较小时可以使得变形量分布更为均匀。
[Abstract]:High speed centrifugal pump is a specific speed centrifugal pump 150~300, widely used in aerospace engineering, electrical engineering, chemical engineering and other fields. The design optimization for a certain type of high specific speed centrifugal pump in chemical process to carry out relevant research work, and collaborative innovation talent training project school (XTPY201618) of China. The chemical process pump is an important infrastructure in chemical plant, is the largest amount of rotating machinery, plays a key role in the chemical process. In recent years, with the development of social economy, the type of single operation, poor stability, high energy consumption of chemical process pumps have been unable to meet the future requirement for industry 4. The running efficiency of the centrifugal pump greatly the extent to which the key flow components especially decided hydraulic design of impeller, and the main geometric parameters on the blade of the pump internal flow characteristics and the dynamic characteristics of the structure. Sound rules are not comprehensive and thorough research. A company from the point of economic benefit maximization, requirements without changing the main structure only on leaf re design optimization to improve hydraulic efficiency. Therefore, this paper focuses on the key parameters of blade outlet angle, from its external characteristics, internal flow field and the dynamic characteristics of the structures. The characteristics to reveal its mechanism and influence. The contents of this paper and the main innovations are: 1. with a high specific speed centrifugal pump in chemical process as the research object, guarantee the other geometric parameters unchanged in the prototype pump, the design of the 4 blade outlet angle (17 degrees, 27 degrees, 37 degrees. 47 DEG) of the impeller scheme, and the different schemes are unsteady numerical simulation under various conditions. Through the comparative analysis of characteristics, can be found: with the increase of blade outlet angle, rated head increased, this is due to the circumferential speed of export With the blade outlet angle increases with the pump, the basic equations, it is not difficult to find increased lift with export circumferential speed increases, but if the blade outlet angle is too large, it will lead to serious curved blade, the shape of "S" appears, the channel becomes shorter between adjacent blades and the diffusion angle becomes larger, lead to increased water loss, the efficiency will be significantly decreased, especially in the large flow condition become more obvious. The simulation data repeatability characteristics and good numerical prototype pump can verify the predictive value of contrast, research the fluid domain model constructed correctly, the numerical simulation method is reliable for.2. more obvious comparative analysis results thus, more intuitive grasp of the effect of blade outlet angle on the chemical flow characteristics inside the pump impeller, only for the 4 new design model of internal unsteady flow characteristic analysis, through the analysis of the static impeller in cross section The distribution of pressure, turbulent kinetic energy and velocity distribution, flow characteristics on the surface of the impeller shaft normalized helicity distribution and small flow rate condition, in order to reveal the blade outlet angle influence on the internal flow characteristics under different conditions. The results show that: with the increase of impeller blade outlet angle, low pressure fluid region gradually to the export import the direction of diffusion, in the vicinity of the working surface of blade are adverse pressure gradient and low pressure fluid instability prone to aggregation, flow separation; blade outlet angle is too large, the larger the turbulent kinetic energy, the axial vortex caused by increased, especially for the large flow condition, almost expanded to the entire channel; small flow condition the normalized helicity maximum, mean flow is easy to instability, which will produce unstable flow structure, the backflow phenomenon with increasing blade outlet angle and has intensified, and mainly in the near front Recirculation cover surface, this phenomenon and regular instability characteristics of helicity prediction coincide; blade outlet angle spiral impeller is 47 degrees in the degree distribution disorder phenomenon, at the same time, both have positive vortex vortex generation and reverse, greater intensity, which may be due to blade outlet angle increase in the analysis increases contrast caused by.3. is in the wake of impeller sweep 4 schemes under various conditions of pressure pulsation and impeller radial force distribution, in order to reveal the outlet blade angle on the pump internal unsteady flow characteristics influence. The research results show that: in the condition of 1.0Q, and increase the amplitude of pressure fluctuation with the blade outlet angle increases, but the pulsation frequency did not change, the main factors of the pressure pulsation or blade and the tongue of the rotor stator interaction; pressure pulsation under large flow condition is higher than that of small flow conditions To be intense, and the amplitude is generally larger; with the increase of blade outlet angle, time frequency shift to the low frequency trend, indicating blade outlet angle on the flow structure, thus affects the pressure on the 4 schemes under different conditions in the calculation of impeller radial force analysis shows that: the radial impeller are under rated condition the minimum force; blade outlet angle distribution of the radial force of the small flow rate condition the greatest impact; to some extent reduce blade outlet angle can effectively improve the effect of radial force on the impeller to fully reveal the influence of the distribution of.4. blade outlet angle on the dynamic characteristics of pump structure, function for the first time the two-way flow solid coupling under numerically under the rated conditions of each scheme were analyzed and compared. Based on the calculation of the fluid solid coupling effect prediction of the lift value, can be found under the action of fluid solid coupling predictive value than the non fluid solid coupling By the prediction value is low, but the simulation error is significantly reduced; comparative analysis of equivalent boundary stress distribution, the results show that the equivalent blade angle on the back of the blade and the front cover plate at the junction of the stress distribution has little effect on the working surface of blade and the front cover of the demarcation line in 0.6 times to 0.8 times the export export the position and the blade working surface and the back boundary line in 0.8 times exports to position a great impact, and the equivalent stress increases with the blade outlet angle; in addition, the stress concentration phenomenon appeared near the exit; calculation on the rated condition of 4 impeller deformation can be found: reduce the blade outlet angle helps reduce deformation, improve the deformation distribution of the impeller impeller; comparative analysis shows that the maximum equivalent stress, blade outlet angle is too large, will cause the maximum equivalent stress is too large, too small will The dynamic load brought alternating greatly; flow dynamic characteristics of impeller structure and solid coupling show that the impeller the first 4 order natural frequency under the program is far greater than 1 times the frequency of leaf, while also avoiding the two harmonic and three harmonic frequency, select the blade outlet angle is larger, is helpful to improve the natural frequency however, too large will cause vibration greatly swing and twisting, smaller deformation can make the distribution more uniform.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.21

【参考文献】