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

为了阐明高比速型开式冠状离心叶轮内不稳定流动的产生机理，分析环形槽布置对诱导轮失速的影响以及扩压器宽度对扩压器失速的影响，进行了三维湍流模拟和实验研究。发现定常流动模拟对理解非定常失速现象很有帮助，并得出以下结论：(1)初期不稳定流动是由邻近叶片压力侧附近的升压涡流动引起的，这是叶尖泄漏流动与积累的逆流区相互作用的结果，其中由于叶尖泄漏涡似乎包含了强向流涡分量。(2)进气道再循环的形成对于抑制诱导轮失速引起的不稳定流动是非常有效的，一个因素是叶尖泄漏涡的吸力与转速的增加增加了流动，另一个因素是由于进气道再循环流量的增加而减小了流动发生率，随着通流量的减小而增加。(3)吸力环槽的最佳位置是在诱导叶尖喉部附近的区域，可以抑制诱导叶失速（即使在设计流量下也不会影响叶轮特性）。(4)扩压器失速引起的不稳定流动发生在逆流区延伸至扩压器出口时。(5) φ=0.278 ~ 0.213之间的不稳定流动可以通过将扩压器宽度从叶轮出口高度减小到扩压器进口到R=1.2之间的三分之二来抑制，扩压器内的压力恢复没有恶化。(6)采用诱导器进口环形槽布置和扩压器出口扩压宽度的减小，使试验风机的不稳定流动范围从φ=0.316减小到0.174，总体上减小了45%左右。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