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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。
Three weeks of unsteady numerical calculations for three types of Krain impellers without a casing, with a circumferential casing, and with an axial casing were performed by using “staggered blade” and “downstream variable area nozzle” Method to simulate the unsteady flow field of the impeller under low flow conditions. The numerical results show that the method of “staggered blade” and “downstream variable area nozzle” does not necessarily trigger the rotationally-stalled vortex in the centrifugal impeller. The unsteady pulsation frequency of the flow field parameters is mainly the blade swept Nth harmonic of frequency. Circumferential casing treatment can effectively reduce the pulsation amplitude of the flow field upstream of the impeller, while the reduction of the axial casing is very weak. The fluid in the receiver is mainly returned to the impeller main channel near the leading edge surface, which is one reason that the receiver handles expanding the stall margin of the impeller.