2020 Volume 13 Issue 2 Pages 485-502
An essential parameter governing the surge behaviors in compressor systems was found on the basis of numerical-experimental results by surge simulations. It is named “flowpath-average reduced resonance frequency”, consisted of the resonance frequency, the total flowpath length and the average velocity. The reduced frequency normalized by the compressor tip Mach number tends to be basically about 1.5 at the stall stagnation boundaries for compressors having few stages and low pressure-ratios, although the value could vary to some extent affected by various circumstantial factors. It means that the stall stagnations could be caused by insufficient number of times of excitations by the resonant frequency on the fluid particles in passing through the whole flowpath. Deep surges tend to occur for the parameter values greater than around 1.5. On the foundation of the normalized flowpath-average reduced resonance frequency can be formed a basic framework for the surge behaviors in terms of non-dimensional surge frequencies and stall-stagnation points. In reference to the framework, several general features of the surge behaviors are described in a relatively unified manner, including the behaviors of surge frequencies and stall stagnation boundaries, which are affected in a complicated manner by compressor conditions of speeds, pressure ratios, and number of stages, and flowpath geometries, relative compressor locations in the flowpath, etc. The framework contributes much to clarification of the characteristic behaviors in surges hitherto unexplained and could provide keys to further surge studies. It could also be useful to devise countermeasures against stall stagnation problems.
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