Development of a Transonic Compressor with a Wide Flow Range

虽然跨音速离心式压缩机的压比非常高，但在给定的轴速下，它几乎不能改变流量，因此很少用于工业应用。本课题对叶轮进行了设计和试验，明确了决定流量范围的失速和堵塞问题。首先，利用准三维流动分析方法，结合文献中的经验关系，开发了叶轮设计的CAD系统。为了避免诱导管内的强烈激波，叶片的曲率在喉部处被做得很弱。在出口处，叶片向后倾斜40度，以达到稳定的特性。为了在试验中保证良好的边界条件，必须在下游安装无叶扩压器，同时压缩机的失速极限不应受扩压器的影响。因此，采用了极短无叶扩压器。除叶轮特性外，还利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、叶冠沿线的压力分布以及诱导器附近的激波行为。用流动分析计算的进气道马赫数和入射角与激光测速仪在亚音速进气道条件下的实测数据吻合较好。然而，在超音速进口条件下，激波的产生不仅改变了流型，而且改变了诱导轮失速的原因。因此，需要一种新的超音速进气道失速判据。短叶片扩压器和通道扩压器组合的叶轮将在不久的将来进行试验。

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.