2019 Volume 12 Issue 4 Pages 302-321
Essential causes of stall stagnations in systems of a compressor and flowpaths were examined with emphasis on axially travelling wave conditions of small disturbance oscillations in a simplified model of the system. The situation could be measured in terms of both the total phase differences across the whole flowpath and the phase differences experienced by the fluid particles in passing through the whole flowpath. In the situation where the total phase difference is larger, the average accelerations of the fluid mass tend to be smaller. On the other hand, when the phase difference of the passing fluid particles is smaller, the fluid particles tend to be excited by two frequencies separated much by modulations similar to Doppler shift effect. The situation tends to disorder the intrinsically synchronous oscillations of the flow and to suppress the fluid motion amplitudes. Both effects tend to result in the stall stagnations in the system. The behaviors of the phase-related parameters were compared with those of the stall-stagnation boundaries predicted by simulations on single-stage compressors. From the fairly good coincidences between both behaviors in the neighborhood of stagnation boundaries, the phase phenomena could be considered as one of possible candidates for the essential cause of the stall stagnations.
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