缝隙引流叶片提高低比转速离心泵性能的机理研究

发布时间：2018-05-29 21:43

本文选题：低比转速离心泵 + 缝隙引流叶片　；参考：《上海大学》2014年博士论文

【摘要】：低比转速离心泵应用广泛，但其效率却偏低。在实际运行过程中，也可能会发生空化，致使泵的性能下降，甚至影响机组运行。提高低比转速离心泵的水力性能和抗空化性能，对于保证机组的安全、稳定和高效运行意义重大。前期研究工作证明基于流动控制思想设计的带有缝隙引流叶片的叶轮在一定的工况范围内可提高离心泵的水力性能。然而目前对其内部流动机理尚缺乏清晰的认识，对该离心泵的空化特性也缺乏考量，也没有一套有效的数值预测方法可以较为准确地描述带有缝隙引流叶片的离心泵内部流动结构。作者在发展一套含多尺度特征的数值预测方法的基础上，系统地开展了缝隙引流叶片式低比转速离心泵内部流动的数值和实验研究工作，旨在探索其内部流动机理，为低比转速离心泵的优化设计、性能预测和流动控制提供理论、数值和实验基础。全文的主要工作如下：一、发展尺度自适性分离涡模拟方法通过引入基于局部流场信息的冯·卡门尺度，对传统DES方法进行了修正，并经过多个算例测试，验证了该方法的有效性。新发展的尺度自适应性分离涡模拟SDES方法改进了传统DES方法在分区辨识方面存在直接依赖网格的不足，可实现稳态与非稳态区域自适应性切换RANS/LES方法进行求解。二、离心泵内部流场PIV实验研究搭建了适用于离心泵性能实验、PIV流场实验和空化观察实验的闭式实验平台，设计并制作了便于PIV流场测量和空化观察实验的离心泵模型。水力性能测试结果表明，随着流量的增大，缝隙引流叶轮的效果逐渐显现，设计的模型泵外特性再现了缝隙引流叶片离心泵的主要特征。PIV流场测试结果表明，离心叶轮内部的流动在各流量工况下主要沿叶片吸力面侧流动，在压力面侧流道内存在一个与叶轮转动方向相反的旋涡。随着流量的增大，涡旋的强度会受主流的抑制而逐渐减弱，并逐步被约束在近压力面侧的较小范围内。三、缝隙引流叶片提高离心泵水力性能的数值研究采用获得的离心泵水力性能和PIV流场实验数据对SDES方法进行了验证，在此基础上，通过数值实验对比分析了传统叶轮和缝隙叶轮离心泵内部流动特性之间的差异，探讨了缝隙叶轮在一定的工况范围内提高离心泵水力性能的机理，认为缝隙叶轮前缘小叶片会导引部分流体经缝隙从叶片压力面侧流向吸力面侧，且前缘偏置和重叠设计的小叶片增大了流道进口区面积，使得流道内部速度场分布更加均匀，从而降低了强剪切湍流引起的叶轮内能量损失。此外，还发现缝隙叶轮离心泵内的压力脉动强度总体低于传统叶轮离心泵，这说明缝隙引流叶片结构还有望提高离心泵的运行稳定性。四、离心泵空化实验研究为考察缝隙引流叶轮离心泵的抗空化特性，分别针对传统叶轮和缝隙引流叶轮离心泵，开展了多个流量工况下的空化性能实验、高速摄影和锁相拍照的空化观察实验。结果表明缝隙引流叶轮在大流量工况区比传统叶轮有更好的抗空化特性，而在小流量工况下，两种叶轮的空化特性基本相当；在大流量工况区，缝隙引流叶轮发生空化的位置主要集中于叶片吸力面侧，随着空化数的降低，，空穴占据流道的体积表现为逐步从叶片吸力面侧向压力面侧增长。而传统叶轮则在叶片前缘压力面较早发生空化，随着空化数的降低，空穴会从进口区流道两侧同时向中间增长。五、缝隙引流叶片提高离心泵空化性能的数值研究在空化实验数据验证的基础上，应用SDES方法对传统叶轮和缝隙引流叶轮离心泵在不同的流量工况下进行了空化流场数值模拟，并分别针对离心泵空化流场的周向演化特征、大流量工况出现的隔舌空化现象、缝隙引流叶轮离心泵在小流量工况出现的交错固定空化现象以及缝隙引流叶轮的抗空化机理进行了详细分析。结果表明缝隙引流叶轮前缘小叶片的导流、缝隙叶片结构的引流以及小叶片对主叶片的扰动应是其抑制空化的发生和发展的主要原因；在蜗壳轴向中心平面上，等半径圆弧上的平均静压力总体上呈现随着向蜗壳出口区域靠近而逐渐减小的趋势，因此叶轮流道出口向蜗壳出口靠近时空化增强，而远离时空化减弱；在大流量工况下，发现在隔舌区发生了空化，并会引起离心泵扬程下降。这是由于大流量工况改变了绕流蜗壳隔舌的入流攻角，引起了隔舌靠近蜗壳出水管的面产生局部分离的低压空化区。绕流隔舌的外部环境压力随叶片周向位置的变化决定了隔舌空化的周向演化特征；流量变化、一定体积空穴区的形成和缝隙射流的共同作用引起了绕流叶片的入流角发生了变化，从而使得缝隙引流叶轮离心泵在小流量工况下出现了相间（交错）流道固定空化现象。综上，尺度自适性SDES方法为离心泵内部流动分析提供了一种有效的数值手段。实验和数值的研究结果均表明，基于流动控制思想设计的缝隙引流叶片结构具有导、引流作用，可在一定的工况范围内同时提高低比转速离心泵的水力性能和抗空化性能。
[Abstract]:The low specific speed centrifugal pump is widely used, but its efficiency is low. In the process of actual operation, cavitation may also occur, which can cause the performance of the pump to decline and even affect the operation of the unit. It is of great significance to improve the hydraulic performance and anti cavitation performance of the low specific speed centrifugal pump for ensuring the safety, stability and efficiency of the unit.
The previous research proves that the impeller with the flow control idea designed with the gap drainage blade can improve the hydraulic performance of the centrifugal pump in a certain range of working conditions. However, there is still a lack of clear understanding of the internal flow mechanism and the lack of consideration on the cavitation characteristics of the centrifugal pump, and there is no effective set of numerical prediction parties. The method can accurately describe the internal flow structure of centrifugal pumps with slot drainage blades.
On the basis of developing a set of numerical prediction method with multi-scale characteristics, the numerical and experimental research work on the internal flow of a low specific speed centrifugal pump with gap drainage is carried out systematically. The purpose is to explore the internal flow mechanism and provide the theory, numerical value and numerical value for the optimization design, performance prediction and flow control of the low specific speed centrifugal pump. The main work of the full text is as follows:
One, development scale self-adaptive separation vortex simulation method
By introducing the von Carmen scale based on the information of local flow field, the traditional DES method is modified, and the effectiveness of the method is verified by several examples. The new developed scale adaptive separation vortex simulation SDES method improves the shortage of the traditional DES method in the partition identification square directly dependent on the grid, and can realize the steady state. The adaptive switching RANS/LES method is applied to solve the problem.
Two, PIV experimental study on internal flow field of centrifugal pump
A closed test platform is built for centrifugal pump performance test, PIV flow field experiment and cavitation observation experiment. A centrifugal pump model is designed and produced to facilitate the measurement of PIV flow field and cavitation observation. The hydraulic performance test results show that the effect of the gap drainage blade gradually appears with the increase of flow rate and the design of the model outside the pump. The main characteristics of the centrifugal pump with gap drainage blade centrifugal pump.PIV flow field test results show that the flow inside the centrifugal impeller is mainly flowing along the suction side of the blade under each flow condition, and the vortex in the side channel of the pressure surface is in the opposite direction to the rotating direction of the impeller. With the increase of the flow, the strength of the vortex will be suppressed by the mainstream. Gradually weakened, and gradually restricted to the smaller side of the near pressure side.
Three, numerical study on improving hydraulic performance of centrifugal pump with slot drain blades
By using the hydraulic performance of the centrifugal pump and the experimental data of the PIV flow field, the SDES method is verified. On this basis, the difference between the flow characteristics of the centrifugal pump and the centrifugal pump of the traditional impeller and the gap impeller is analyzed by the numerical experiments. The mechanism of the gap impeller to improve the hydraulic performance of the centrifugal pump in a certain range of working conditions is discussed. The blade of the front edge of the gap impeller leads to the flow of some fluid through the gap from the blade pressure side to the suction surface, and the area of the inlet area of the channel is increased by the bias and overlap of the front edge, which makes the velocity distribution in the channel more uniform, thus reducing the energy loss in the impeller caused by the strong shear turbulence. In addition, the gap is also found. The pressure pulsation strength of impeller centrifugal pump is lower than that of traditional impeller centrifugal pump. This shows that the structure of slot drain blade is also expected to improve the operation stability of centrifugal pump.
Four, experimental study on cavitation of centrifugal pump
In order to investigate the cavitation resistance characteristics of the centrifugal pump of the gap drainage impeller, the cavitation performance experiments of the centrifugal pumps with the traditional impeller and the gap drainage impeller were carried out respectively. The results showed that the gap drainage impeller had better cavitation resistance than the traditional impeller in the large flow condition. The cavitation characteristics of the two kinds of impellers are basically equal in the small flow condition. In the large flow condition, the cavitation position of the gap drainage impeller mainly concentrates on the suction side of the blade. With the decrease of the cavitation number, the volume of the hole occupying channel increases gradually from the side pressure side of the blade suction surface. Cavitation occurs at the leading edge of the blade, and with the decrease of cavitation number, the hole will grow from the inlet to the middle.
Five, numerical study on improving cavitation performance of centrifugal pump with slot drain blades
On the basis of the verification of the cavitation experiment data, the SDES method is used to simulate the cavitation flow field of the centrifugal pump of the traditional impeller and the gap drainage impeller under different flow conditions, and the characteristics of the circumferential evolution of the cavitation flow field of the centrifugal pump, the cavitation phenomenon in the large flow condition and the small flow of the centrifugal pump of the gap drainage impeller in the small flow are taken. The staggered fixed cavitation and the anti cavitation mechanism of the gap drainage impeller are analyzed in detail. The results show that the diversion of the blade of the front edge of the gap drainage impeller, the drainage of the structure of the gap blade and the disturbance of the leaf blade to the main blade should be the main reason for the development and development of the cavitation. On the heart plane, the average static pressure on the arc of the equal radius is gradually decreasing as the outlet area of the volute is near, so the outlet of the outlet of the impeller flow to the volute is close to the space-time enhancement, but it is far away from the time and space, and the cavitation occurs in the tongue zone in the large flow condition and will cause the drop of the centrifugal pump head to fall. This is due to the change of the angle of attack on the tongue of the spiral case, which causes the local separation of the low pressure cavitation area near the surface of the outlet pipe of the volute. The external environmental pressure of the tongue around the tongue determines the circumferential evolution characteristic of the tongue cavitation with the change of the circumferential position of the blade; the flow change, the shape of a certain volume hole area The interaction between the formation and the slit jet causes the change of the inflow angle of the flow around the blade, which makes the centrifugal pump of the gap drainage impeller appear the phenomenon of the fixed cavitation in the interphase (interlaced) flow channel under the small flow condition.
To sum up, the scale self-adaptive SDES method provides an effective numerical method for the internal flow analysis of centrifugal pumps. Both experimental and numerical results show that the structure of the gap drainage blade based on the flow control idea has the guiding and drainage effects, and the hydraulic performance of the low specific speed centrifugal pump can be improved simultaneously in a certain range of working conditions. And anti cavitation performance.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH311

【参考文献】