双向轴流泵的优化设计及内流特性研究

发布时间：2018-10-25 07:45

【摘要】：叶轮机械内部三维流场的非定常流动机理及控制是学科研究热点问题之一,双向轴流泵作为兼顾排涝和灌溉的低扬程泵站的主要“心脏”部件,多为采用传统二元方法设计的S型叶片,存在正、反向运行条件不同时能效较低的缺陷,反向时由于导叶起正预旋作用,且无后置导叶整流,其内流结构中的逆压梯度变化、附面层分离、大尺度回流等特殊复杂流动制约了综合性能的提升,论文采用理论分析、数值模拟与试验相结合的方法,围绕非对称翼型双向轴流泵的优化设计、内流机理及主/被动流动控制技术、压力脉动特性等方面内容开展研究,取得如下成果：(1)基于保角变换法提出了一种低拱度圆弧翼型双向叶片设计方法,通过儒可夫斯基变换建立低拱度圆弧翼型正反向速度环量、理论扬程的关系,通过改变叶栅几何参数分配正反向性能,同时基于升力法设计常规S翼型双向轴流泵开展对比研究,系统对比了两种翼型叶片双向轴流泵的时均流场和压力脉动特性,通过在叶片、导叶表面网格上创建微小网格单元并监测其平均压力研究了S翼型双向轴流泵正反向运行时叶片、导叶表面的压力脉动变化规律,对比了正反向马鞍区流动特性及叶顶间隙流动特性,开展两个模型正反向不同安放角下的实验研究。结果显示,圆弧翼型叶片吸力面尾缘附近流体质点的径向运动较小,进出口边脉动幅值更低,正反向效率较S翼型模型分别高3.5%和1.3%；叶片表面压力脉动主要受导叶叶片数影响,主频为导叶通过频率,导叶表面压力脉动的主频为叶片转动频率；小流量下,正向时在1～2、4～5倍转频,反向时在0～2倍转频出现了较强的低频脉动。(2)开展双向轴流泵导叶改型设计研究,建立了弯导叶双向轴流泵反向运行内流场流动模型,引入直导叶以降低反向时叶片吸力面大冲角入流,基于Q等值面法研究了直导叶内的旋涡结构及其非定常演变规律,通过改变翼型降低流动分离强度；分析了导叶一弯管相对位置变化对流场结构及性能的影响规律。结果表明,直导叶可消除反向时叶片前的正预旋,后置直导叶内主要流动损失由吸力面附面层分离及脱落涡引起,合理选择翼型可以降低流动分离强度；弯管会破坏上游流场的轴对称分布,改变导叶各叶片的冲角。(3)构建了同时包含叶片、流道几何参数的轴流泵(风机)参数化优化平台,改进现有轴流叶片优化方法,提出一种包含实验设计和速度梯度算法的轴流式叶片组合优化方法,基于最优拉丁超立方方法及序列二次规划算法分别对叶片、流道进行优化,通过增大空间步长加速收敛。较常规直接采用实验设计或序列二次规划算法优化正向效率分别提高了3.07%和0.87%,采用扩散管减小了流道径向压差和流体周向旋转速度,对叶片和流道优化后正向效率较原模型分别提高了2.02%和2%。
[Abstract]:The unsteady flow mechanism and control of three-dimensional flow field in turbomachinery is one of the hot topics in academic research. Two-way axial flow pump is the main "heart" component of low lift pump station which takes both drainage and irrigation into account. Most of the S-type blades designed by traditional binary method have the defects of low energy efficiency in both positive and reverse operation conditions. In reverse, due to the prerotation of the guide vane and no rectification of the rear guide vane, the reverse pressure gradient changes in the internal flow structure. Special complex flow such as boundary layer separation and large scale reflux restrict the improvement of comprehensive performance. This paper uses the method of theoretical analysis, numerical simulation and test to optimize the design of asymmetric airfoil bidirectional axial flow pump. The internal flow mechanism, active / passive flow control technology, pressure fluctuation characteristics and so on are studied. The results are as follows: (1) based on the conformal transformation method, a design method for low arch circular arc airfoils is proposed. The relationship between forward and inverse velocity loop and theoretical head of low arch circular arc airfoil is established by means of Jokovsky transform. By changing the geometric parameters of cascade, the positive and negative performance is assigned. At the same time, based on the lifting method, the design of conventional S airfoil bidirectional axial flow pump is compared, and the time-averaged flow field and pressure pulsation characteristics of two kinds of airfoil bi-directional axial flow pumps are systematically compared, and the flow field and pressure pulsation characteristics of two kinds of airfoil bi-directional axial flow pumps are compared. A micro mesh cell was created on the surface of the guide vane and its average pressure was monitored. The variation of pressure fluctuation on the surface of the guide vane during the forward and backward operation of the S airfoil bidirectional axial flow pump was studied. The flow characteristics of the positive and backward saddle region and the tip clearance flow characteristics were compared. The experimental study of the two models was carried out under different forward and backward placement angles. The results show that the radial motion of fluid particles near the trailing edge of suction surface of circular arc airfoil is smaller, the pulsation amplitude of inlet and outlet edge is lower, and the positive and negative efficiency is 3.5% and 1.3% higher than that of S airfoil model, respectively. The pressure pulsation on the surface of the blade is mainly affected by the number of pieces of the guide blade, the main frequency is the passage frequency of the guide vane, the main frequency of the pressure pulsation on the surface of the guide vane is the rotating frequency of the blade; In reverse, a strong low frequency pulsation occurs at 0 ~ 2 times of rotation frequency. (2) the design of guide vane of bidirectional axial flow pump is studied, and the flow model of flow field in reverse operation of bending-guide vane bidirectional axial flow pump is established. In order to reduce the inlet flow of suction surface, the vortex structure and its unsteady evolution in the blade are studied based on the Q iso-surface method, and the flow separation strength is reduced by changing the airfoil. The influence of the relative position of the guide vane-elbow on the structure and performance of the flow field is analyzed. The results show that the direct guide vane can eliminate the positive prerotation in the front of the blade and the main flow loss is caused by the separation of the suction boundary layer and the shedding vortex. The reasonable selection of the airfoil can reduce the flow separation strength. The curved pipe will destroy the axial symmetrical distribution of the upstream flow field and change the angle of attack of the blades. (3) the parametric optimization platform of axial flow pump (fan) including the geometric parameters of blade and passage is constructed to improve the existing optimization method of axial flow blade. An axial flow blade combination optimization method including experimental design and velocity gradient algorithm is proposed. The blade and channel are optimized based on the optimal Latin hypercube method and sequential quadratic programming algorithm. The convergence is accelerated by increasing the space step size. Compared with the conventional direct experimental design or sequential quadratic programming algorithm, the forward efficiency is increased by 3.07% and 0.87%, respectively, and the radial pressure difference and the circumferential rotation velocity of the fluid are reduced by using the diffusion tube. Compared with the original model, the forward efficiency of blade and channel optimization is increased by 2.02% and 2% respectively.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH312

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