Studies on Reverse Flow in Centrifugal Impeller

离心叶轮逆流研究

• 批准号: 61460099
• 负责人: TOYOKURA Tomitaro
• 金额: $ 3.46万
• 依托单位: Faculty of Engineering, Yokohama National University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1986
• 资助国家: 日本
• 起止时间: 1986 至 1987
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-61460099/
• 关键词: Reverse Flow; Centrifugal Impeller; Cavitation; Centrifugal Pump; 非定常流; 非定常計測; オープン羽根車

In order to avoid the choke resulted from the cavitation and to improve the performance of centrifugal pump, it is more often to take a large blade inlet angle and a big inlet diameter. In this case, on the contrary, there has a tendency to cause the cavitation based on the reverse flow in the suction side of impeller blades. Consequently, it needs to clarify the mechanism of this reverse flow which has hardly been investigated, although it is very complicated. So, this paper aims at making the mechanism occurence of the reverse flow clear and acquiring the knowledge in connection with the cavitation.Since an axisymmetric property of the blade inlet flow disappears when the reverse flow happens, the position occurence and the scale of the reverse flow can not be obtained by the steady measurement. Accordingly, at first an unsteady measurement with use of pitot tube was established. Then, the pump performances and the relation between the reverse flow and the pressure distributions in t … More he impeller passage were investigated by using the open impeller. The achievements were gained as follows. As the blade inlet angle is large, when the flow rate is 95% of the maximum efficiency point (equivalent to the flow rate 45% of the shockless flow condition), the inlet flow has already changed considerably in the pitch direction, which seems that the reverse flow happens easigy, and this reverse flow can be observed when the flow rate becomes 90%. The scale of the reverse flow is so large that the whole region of one pitch between the blades near by the blade tip is occupied by the reverse flow but its region decreases gradually in the blade height direction and is limited near the leading edge at the place of 1/4 blade height. Furthermore, even the flow rate decrases much more, the reverse flow region on the blade inlet section hardly changes and enlarges to the upstream side. When the reverse flow occurs, the pressure increases greatly on the wide region of the negative pressure side near the blade inlet and the pressure increase can be observed locally even near the pressure side. As the reason of those phenomena, it can be considered that the former is affected by the secondary flow running to the suction cover side along the blade surface while the later is caused by the movement of stagnation point of the leading edge toward the pressure side. This fact has been confirmed also by the visible result derived from the oil film method. Besides, the pressure discributions on the blade surface show a same tendency with the one derived from the singularity method, except the leading edge neigbourhood, but the experimental value on the negative surface is smaller than the calculating one. Moreover, the influence of blade tip clearance width on he reverse flow scale and on the pressure distributions between the blades seems to limited. Less

为了避免汽蚀造成的阻塞，提高离心泵的性能，往往采用大叶片进口角和大进口直径。相反，在这种情况下，存在基于叶轮叶片的吸入侧中的逆流而引起气穴的趋势。因此，它需要澄清的机制，这种反向流动几乎没有被调查，虽然它是非常复杂的。本文的目的是弄清反流发生的机理，获得与空化有关的知识，由于反流发生时叶片进口流场的轴对称性消失，因此，用定常测量方法无法确定反流发生的位置和规模。因此，首先建立了用皮托管进行非定常测量的方法。在此基础上，分析了泵的性能，以及泵内回流与压力分布的关系， ...更多信息 采用开式叶轮对叶轮流道进行了研究。取得了以下成果。由于叶片进口角较大，当流量为最大效率点的95%时（相当于无激波条件下的流量45%），进口流动在桨距方向上已经发生了很大的变化，似乎很容易发生逆流，当流量为90%时可以观察到这种逆流。回流的规模很大，以致于靠近叶尖的叶片之间的一个节距的整个区域都被回流占据，但其区域在叶片高度方向上逐渐减小，并在1/4叶片高度处的前缘附近被限制。此外，即使流量减少得更多，叶片入口截面上的逆流区域也几乎不改变，并且向上游侧扩大。当发生反向流动时，在叶片进口附近的负压侧的宽区域上的压力显著增加，并且甚至在压力侧附近也可以局部地观察到压力增加。对于这些现象的原因，可以认为前者是由于二次流沿叶片表面沿着流向吸力面一侧，而后者是由于前缘驻点向压力面一侧移动。这一事实也被油膜法的可见结果所证实。除前缘附近外，叶片表面的压力分布与用奇异性方法得到的结果趋势一致，但负表面的实验值小于计算值。此外，叶顶间隙宽度对回流尺度和叶间压力分布的影响似乎是有限的。少