Investigation of the spike-stall warning method using the blade passing signal

Abstract

The vaned-diffuser usually brings compressor instability problems under the small flow rate, for instance the spike-type rotating stall phenomenon which restricts the operation range and may cause the trouble of blade fatigue. Since it is difficult to mathematically predict the spike-type stall for its randomness, finding out a practical method to warning this stall precursor appears to be meaningful. The paper explains the relationship between the spike-type precursor and the blade passing irregularity coefficient to analyze whether this coefficient is appropriate for the spike-stall warning inside a centrifugal compressor with the vaned-diffuser. The advanced wireless measurements were conducted on a 1.5 stages test centrifugal compressor to capture the unsteady behavior progressing from the design to stall inception within the region between the impeller trailing edge (TE) and diffuser leading edge (LE). The circumferential distribution of the blade passing irregularity has been quantitatively revealed. The steep increase of the blade passing irregularity at some “special locations”, which is responsible for the onset of the spike-type precursor, is highlighted. Also, to further understand the spike precursor inside the diffuser passage corresponding to the circumferential “special location” with maximum irregularity, the high-response transient measurement within this passage is presented. With the help of full-annulus computational fluid dynamics (CFD) simulation and the mathematical model, it is proved that the blade passing irregularity precisely reflects the flow characteristics during the spike precursor, which presents the guidance for this stall warning method.