Investigation of Internal Flow and Characteristic Instability of a Mixed Flow Pump
Investigation of Internal Flow and Characteristic Instability of a Mixed Flow Pump
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DOI：
10.1115/fedsm2009-78277
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发表时间：
2009
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影响因子：
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通讯作者：
Masahiro Miyabe;A. Furukawa;H. Maeda;Isamu Umeki
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文献类型：
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作者：
Masahiro Miyabe;A. Furukawa;H. Maeda;Isamu Umeki
通过使用商业CFD代码和动态PIV（DPIV）测量，在比转速为700（min-1 m3 /min，m）或1.72（无量纲）的混流泵中研究了泵特性不稳定性与内部流动之间的关系。该泵在约60%Qopt和82%Qopt的流量下具有两个正斜率的压头流量特性。在作者的前期研究中，阐明了在82%Qopt处的特征不稳定性是由扩压器旋转失速（DRS）引起的，并且有叶扩压器轮毂附近的回流在扩压器旋转失速的发生中起着重要作用。在本文中，调查的重点是在约60%Qopt的不稳定性。基于实验和数值计算结果，阐明了60%Qopt时的特性不稳定性是由叶轮顶部进口处的回流引起的，从叶轮压力面到吸力面的泄漏流对回流的发生起着重要作用。通过DPIV测量和CFD模拟，可视化了叶轮进口处的回流行为。此外，内部流动进行了详细的研究和发生的特征不稳定性假设如下：在部分流率，在叶轮尖端的入口处的流动角减小，流动撞击叶轮压力面。此时，叶尖进口处的叶片载荷增大，前缘回流量和压力面到吸力面的泄漏量增大。泄漏流导致在叶轮的吸力面的入口处产生涡流。当流量进一步减小时，涡流发展为带旋流的回流。泄漏流具有绝对速度的周向分量，旋流能量由回流连续提供。因此，即使在叶轮入口处的通道流也已经得到预旋流。由于预旋，理论水头，欧拉水头减小。此外，基于CFD结果，叶轮吸力面附近的预旋和非定常涡导致泵特性不稳定。当流量进一步降低时，由于轮毂区域的叶片扩压器的回流，叶轮中的流型变为离心型，因此总压头升高。Copyright © 2009 by ASME
The relationship between pump characteristic instabilities and internal flow was investigated in a mixed flow pump with specific speed of 700 (min−1 m3 /min, m) or 1.72 (non-dimensional) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. This pump has two positive slopes of a head-flow characteristic at the flow rates of about 60%Qopt and 82%Qopt . In the authors’ previous study, it was clarified that the characteristic instability at 82%Qopt is caused by the diffuser rotating stall (DRS) and the backflow near the hub of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. In the present paper, the investigation is focused on the instability at about 60% Qopt . Based on both of experimental and numerical results, it was clarified that the characteristic instability at 60%Qopt is caused by the backflow at the inlet of the impeller tip and the leakage flow from the impeller pressure surface to the suction surface plays an important role on the onset of the backflow. The behaviors of backflow at the impeller inlet were visualized by the DPIV measurements and CFD simulation. Moreover, internal flow was investigated in detail and the occurrence of characteristic instability is assumed as follows: At the partial flow rate, the flow angle at the inlet of the impeller tip decreases and the flow hits the impeller pressure surface. Then, the blade loading at the inlet of impeller tip is increased and the recirculation at the leading edge and the leakage flow rate from pressure surface to suction surface increases. The leakage flow causes to generate vortices at the inlet of the suction surface of the impeller. As the flow rate is further decreased, the vortices develop to backflow with swirl. The leakage flow has peripheral component of absolute velocity and the swirling energy is continuously supplied by the backflow. Therefore, even the passage flow at the inlet of the impeller has been getting pre-swirling. The theoretical head, the Euler head is decreased due to the pre-swirling. Moreover, based on the CFD results, the pre-swirling and unsteady vortices near the suction surface of the impeller causes pump characteristic instability. When the flow rate is decreased further more, total head rises because the flow pattern in the impeller changes to centrifugal type due to the backflow from the vaned diffuser at the hub region.Copyright © 2009 by ASME