Development of a Transonic Compressor with a Wide Flow Range

虽然跨音速离心压缩机具有很高的压比，但在给定的轴转速下，它几乎不能改变流量，因此，它很少用于工业应用。本项目针对决定叶轮流量范围的失速和阻塞问题，设计并试验了一个叶轮。首先，采用准三元流动分析方法，结合文献中的经验关系，开发了一个叶轮设计CAD系统。为了避免在诱导轮中产生强烈的激波，叶片的曲率在喉部之前都很小。为了保证试验中良好的边界条件，在压气机下游安装一个无叶扩压器，但扩压器不应影响压气机的失速极限。因此，采用了很短的无叶扩压器。除叶轮特性外，还用动态压力传感器和激光测速仪研究了叶轮出口处的流动状况、沿围带沿着的压力分布和诱导轮附近的激波特性，在亚音速进气条件下，由流动分析估算的进口马赫数和入射角与激光测速仪的测量数据吻合得很好。但是，在超声速进气条件下，激波的产生不仅改变了流态，而且改变了诱导轮失速的原因。因此，对于超音速进气条件，需要一种新的失速判据。短叶片扩压器和槽道扩压器组合叶轮即将进行试验。

Although a transonic centrifugal compressor develops a very high pressure ratio, it can hardly change the flow rate at a given shaft speed, therefore, it is seldom used for industrial applications. In this project an impeller was designed and tested clarifying the problems relative to stall and choke which decide the flow range.First of all, a CAD system for an impeller design was developed using a quasi-three dimensional flow analysis together with empirical relations in the literature. In order to avoid a strong shock in the inducer, the curvature of blades were made weak up to the throat. At the exit the blades were made backward leaning by 40 deg to achieve stable characteristics.In order to secure good boundary conditions in the test, a vaneless diffuser must be installed downstream while the stall limit of the compressor should not be affected by the diffuser. Therefore,a very short vaneless diffuser was adopted. In addition to the impeller characteristics, the condition of flow at the impeller exit, the pressure distribution along the shroud and the behaviour of shock waves near the inducer were examined using dynamic pressure transducers and a laser velocimeter.The inlet Mach number and the incidence angle evaluated by a flow analysis agreed well with the measured data by the laser velocimeter at subsonic inlet conditions. However, at supersonic inlet conditions shock waves were generated and they not only modified the flow pattern but also changed the cause of inducer stall. Therefore, a new stall criterion is required for supersonic inlet conditions.The impeller combined with short vane diffusers and with channel diffusers will be tested soon.