Eckardt离心叶轮失速流场非定常特征分析

Investigation of Unsteady Characteristics of Rotating Stall on Eckardt Centrifugal Impeller

关键词:  离心压气机  失速  空间傅里叶分析  前缘溢流  低速二次涡

Key words:  Centrifugal compressor  Stall  Spatial fast Fourier transform  Leading edge spillage  Low velocity secondary vortex

摘要:

为明确离心压气机失速流场特征及类型，对Eckardt离心叶轮进行全通道非定常流场模拟， 得到以下失速流场特征结果:(1)叶片前缘叶顶区域明显存在4个突尖型失速团，同时前缘涡、通道涡和低速二次涡共同作用形成流道内的非定常不稳定流动，诱发旋转失速；(2)与轴流叶轮突尖失速特征相似，离心叶轮内同样存在前缘溢流，但不存在尾缘反流，而呈现与径向和周向扭曲结构相关的新特征:叶顶间隙流与流道中的偏转二次流汇合，形成尺度更小、范围更大的低速二次涡。经进一步的空间傅里叶分析，确定失速团以60%～73%的叶轮转速沿周向传播，且由叶轮入口向下游移动，伴随发生涡脱落和破碎，使流场进入深度失速状态。通过分析这些失速流场特征，得出离心叶轮中突尖失速特征与轴流相比既有相同之处也有不同之处的结论。

Abstract:

To investigate the characteristics and the types of rotating stall in centrifugal compressor， the full-annual unsteady numerical simulation with software CFX was carried out on Eckardt impeller. Results show: (1) There exist four spike-type stall cells on the blade leading edge near shroud endwall. The unsteady and unstable flow in the channel is formed by the interaction of the leading edge vortex， the channel vortex and the low-velocity secondary vortex， which induces the rotational stall. (2) Similar to the spike-type stall in axial flow impeller， leading edge spillage also occurs in centrifugal impeller channel. Meanwhile， due to the strong meridian and circumferential twist， the trailing edge backflow shows new characteristics for centrifugal impeller: the confluence of the tip leakage flow and secondary flow lead to multiple smaller-scale secondary vortices in a larger area. A further spatial fast Fourier transform analysis indicates that the spike stall cells move at about 60%～73% of the rotor speed along circumference， and go deep into the downstream of channel with shedding and breakdown of vortices， which makes the flow field deteriorate into deep stall status. Based on the analysis for characteristics of rotating stall， it can be concluded that the characteristics of rotating stall for the leading edge of centrifugal compressor not only show similar aspects but also some different aspects， compared with axial compressor.