Propagation in Two Mismatched Compressor Stages

This Nemorandum describes an investiga%ion into the flow fluctuations occurring in two mismatched otaiges in the N.G.T.E. 106 low speed CCmpre3s0r. It3 pur~~ose is to contribute tn a gener,ll understanding of surgin,-, and unstea:iy flow-phenomena in Pull scale compressors when operating in a mismatched condition. licit wire anemometers were used to ex:lmine the fluctuations, measurements being made before and after each blade row at tioven flow Coefficients. It W2S f'Ound that 'before sui-ge W2S reached, random fluctuations of amplitude urj to nearly 3C per cent of the mean velocity occurred, the am..litude tgSniiing to kxrease as surge was aqpr,oached. The major surge consisted of a singic stsll celi rotating at 35 per cent of thz compressor speed bu t this was preceded by a less noticeable surge which consisted of tlTW2 Cell:; rctating 2-t the same speed. The flow in the annulus outside the stall cells was ;'ound to have a cyclic distribution, v;ith an am@ituOe 01' the order of 50 per cent of the mean velocity, the ccZls occurring in the regions of l.oy:est velocity. The results gxx9-z;ily emphasise the complex nature of the flows occurring in the surg.e a& near surge cenditions, and the dependence of Stall cell propagation in one stqe on interfcZ?nce iki3lll neighkxxxing-. stages.