Response of Backflow to Flow Rate Fluctuations
Response of Backflow to Flow Rate Fluctuations
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回流对流量波动的响应
DOI：
10.1115/1.2427081
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发表时间：
2007
影响因子：
2
通讯作者：
Y. Tsujimoto
中科院分区：
文献类型：
--
作者：
Xiangyu Qiao;H. Horiguchi;Y. Tsujimoto
基于k-e湍流模型，采用三维数值计算方法，研究导流轮入口回流对流量波动的响应，探讨其对空化不稳定性的影响。首先表明，回流区域的大小可以与上游的角动量相关，并且即使在非常低的频率下，回流的相位也显着延迟于准稳态响应。结果表明，边界剪应力影响较小，角动量守恒关系成立。由于引起回流的叶片两端的压力差在所检查的频率下是准稳定的，因此负流提供的角动量被证明是准稳定的。根据角动量平衡和数值计算结果，推导出上游角动量对流量波动的响应函数。这清楚地表明回流作为一阶滞后元件响应流量波动。假设空腔发展的延迟远小于回流的延迟，讨论了回流空化对空化不稳定性的影响。研究发现，由于正质量流量增益因子的影响，回流空化会不稳定低频扰动，但由于空化柔量的影响，回流空化会稳定高频扰动。
The response of backflow at the inlet of an inducer to the flow rate fluctuation is studied by using three-dimensional numerical calculations based on the k-e turbulence model for the discussion of its effect on cavitation instabilities. It is first shown that the size of the backflow region can be correlated with the angular momentum in the upstream and the phase of the backflow significantly delays behind the quasi-steady response even at a very low frequency. It is then shown that the conservation relation of angular momentum is satisfied with minor effects of the shear stress on the boundary. The supply of the angular momentum by the negative flow is shown to be quasi-steady due to the fact that the pressure difference across the blade causing the backflow is quasi-steady at those frequencies examined. A response function of the angular momentum in the upstream to flow rate fluctuation is derived from the balance of the angular momentum and the results of the numerical calculations. This clearly shows that the backflow responds to the flow rate fluctuation as a first-order lag element. The effects of the backflow cavitation on cavitation instabilities are discussed assuming that the delay of cavity development is much smaller than the delay of the backflow. It was found that the backflow cavitation would destabilize low frequency disturbances due to the effects of the positive mass flow gain factor but stabilize high frequency disturbances due to the effect of the cavitation compliance.