Study on Mechanism of Unstable Flow Inception at Small Flow Rates in a Centrifugal Blower

为了阐明高比转速开式离心叶轮内不稳定流动的发生机理，分析导流轮环槽布置方式和扩压器宽度对扩压器失速的影响，对该叶轮进行了三维湍流数值模拟和实验研究。结果表明，定常流模拟对理解非定常失速现象是很有帮助的，并得出以下结论。（1）初始不稳定流动是由邻近叶片压力侧附近的卷起涡流引起的，卷起涡流是由叶顶泄漏流与累积反向流区之间的相互作用引起的，其中由于叶顶泄漏涡而似乎包括强的流向涡分量。（2）进口再循环的形成对于抑制诱导轮失速引起的不稳定流动非常有效，其中一个因素是叶尖泄漏涡的抽吸和涡度的共同作用。 关于我们 RSE流，另一个是由于入口再循环流率的增加而导致的流冲角的减小，入口再循环流率随着通流率的减小而增加。（3）吸环槽的最佳位置在诱导轮叶尖喉部附近，从而抑制诱导轮失速（即使在设计流量下也不损害叶轮特性）。（4）当回流区延伸到扩压器出口时，扩压器失速引起的流动不稳定。（5）通过将扩压器进口与R=1.2之间的扩压器宽度从叶轮出口高度减小到三分之二，抑制了φ=0.278 ~ 0.213之间出现的不稳定流动，使扩压器内的压力恢复不受影响。（6）通过导流轮进口环形槽布置和扩压器出口窄化扩压器宽度，使试验风机的不稳定流量范围从φ=0.316减小到φ = 0.174，共减小了约45%。少

In order to clarify the mechanism of the unstable flow inception in a high specific speed type open shrouded centrifugal impeller, and to analyze the effect of the ring groove arrangement on inducer stall and/or that of the diffuser width on diffuser stall, the 3-D turbulent flow simulation and the experimental work were performed. It was found that the steady flow simulation was very helpful for understanding unsteady stall phenomena, and the following concluding remarks were obtained.(1)The incipient unstable flow is caused by the rolling-up vortex flow near the pressure side of the adjacent blade, resulting from the interaction between the tip leakage flow and the accumulated reverse flow zone, in which the strong streamwise vorticity component seems to be included due to the tip leakage vortex.(2)The formation of inlet recirculation is very effective for suppression of the unstable flow due to inducer stall, one factor is the suction of the tip leakage vortex together with the reve … More rse flow, and another one is a decrease in the flow incidence due to an increase in the inlet recirculation flow rate, which increases with a decrease in the through-flow rate.(3)The optimum location of the suction ring groove is in the region near the inducer tip throat, resulting i n suppression of inducer stall (without deterioration of the impeller characteristics even at the design flow rate.(4)The unstable flow due to diffuser stall occurs when the reverse flow zone extends to the diffuser exit.(5)The unstable flow occurring between φ=0.278 and 0.213 was suppressed by reducing the diffuser width from the impeller exit height to two-thirds between the diffuser inlet and R=1.2, by which the pressure recovery in the diffuser is not deteriorated.(6)The unstable flow range of the test blower was reduced significantly by about 45% in total from φ=0.316 to 0.174 by implementing the ring groove arrangement for the inducer inlet as well as the narrowed diffuser width for the diffuser exit. Less