近失速压力扰动的试验

Experimental Study of Pre-Stall Pressure Disturbances in a Low-Speed Axial Compressor

采取在静子叶片表面埋入微型压力传感器的方法,对叶尖、叶中和叶根3个截面上的动态压力进行测量,实验研究了压气机近失速的流场特性。实验结果表明:压气机失速前,存在两个特征频率的压力扰动;这两个特征扰动的扰动频率与压气机转速成正比,与转子转动频率的相对频率分别等于5和8;相对频率为5的特征扰动强度随着流量系数减少而增大,在失速点达到最大,而相对频率为8的特征扰动随着流量系数减少先增大,在失速点突然下降;选择相对频率为5的特征扰动作为压气机失稳预警信号,设定某一λ值作为报警的阈值,可以有效防止压气机失速。

The dynamic pressure on stator surfaces at vane tip,mid-span and root was measured to demonstrate the flow structure in a compressor working close to its stability limit. Unsteady pressure signals show that before stall there exist two kinds of pressure disturbances. The frequencies of these disturbances are approximately in proportion to rotor speed and the relative frequencies are 5 and 8 respectively in terms of rotor rotating frequency. The intensity of the disturbance with relative frequency 5 increases as mass flow decreases until compressor working point reaches stall margin ,whilst the intensity of other disturbances increases first and drops suddenly as compressor works at stall point. Thus,the flow field disturbance which leads to rotating stall/surge should be that the relative frequency is 5 and it can be regarded as the warning signal of instability. Setting a value λ as the threshold ,establishing a reliable and effective stall avoidance control based on pressure signals detected by high response transducers seems to be promising.