离心式叶轮机匣处理的整周非定常数值分析

Whole-Annulus Unsteady Flow Analysis on a Centrifugal Impeller With the Casing Treatment

针对不带机匣、带周向机匣和带轴向机匣的三种类型的Krain叶轮进行了整周非定常数值计算,通过使用"交错叶片"和"下游变面积喷嘴"的方法来模拟小流量工况下叶轮的非稳定流场特性。数值计算结果表明,"交错叶片"和"下游变面积喷嘴"的方法并不一定能触发离心式叶轮中的旋转失速涡团,流场参数的非定常脉动频率主要是叶片扫掠频率的N次谐波。周向机匣处理可以有效的减小叶轮上游流场的脉动幅度,而轴向机匣的减小程度很微弱。机匣中的流体主要在前缘面附近返回到叶轮主流道,这是机匣处理扩大叶轮失速裕度的一个原因。

The whole-annulus unsteady flow analysis are carried out on three types of Krain impeller： one is without the casing treatment,and the other two are added the casing treatments with the circumferential or axial grooves respectively.The unsteady flow characteristics under the low flow rate condition are simulated by the ＂mis-staggered blade＂ method and the ＂downstream variable-area nozzle＂ method.The results show that,the rotating stall inception is not always predicted by the use of the two methods.The unsteady fluctuation frequencies of flow parameters are mainly equal to the Nth harmonic frequency of blade passing frequency.The casing treatment with the circumferential grooves reduces the fluctuation amplitude of the flow upstream of the impeller effectively,whilst that with the axial grooves reduces the flow fluctuation amplitude slightly.The fluid in the casing treatments returns to the impeller passage mostly near the blade leading edge,which is one of the reasons for enlarging the stall margin of impeller.