Surge Phenomena Analytically Predicted in a Multi-stage Axial Flow Compressor System in the Reduced-Speed Zone

Abstract

Surge phenomena in the zone of reduced speeds in a system of a nine-stage axial flow compressor coupled with ducts were studied analytically by use of a surge transient simulation code. Main results are as follows. (1) Expansion of apparently stable, non-surge working area of the pressure vs. flow field beyond the initial stage-stall line was predicted by the code in the lower speed region. The area proved analytically to be caused by significantly mismatched stage-working conditions, particularly with the front stages deep in the rotating stall branch of the characteristics, as was already known in situ and in steady-state calculations also. (2) Surge frequencies were found to increase for decreasing compressor speeds as far as the particular compressor system was concerned. (3) The tendency was found to be explained by a newly introduced volumemodified reduced surge frequency. It suggests that the surge frequency is related intimately with the process of emptying and filling of air into the delivery volume. (4) The upstream range of movement of the fluid mass having once passed through the compressor in surge was found to reduce toward the lower speeds, which could have caused additionally the increase in surge frequency. (5) The concept of the volume-modified reduced surge frequency was able to explain, though qualitatively at present, the behaviors of the area-pressure ratio parameter for the stall stagnation boundary proposed earlier by the author.

A Study on the Fundamental Surge Frequencies in Multi-Stage Axial Flow Compressor Systems

“…It is expected also that the parameter could relate the surge frequencies at the stall stagnation boundaries as the limiting condition with those for changing compressor speeds. In the analytical results about a nine-stage compressor in Yamaguchi [11], the volumemodified reduced surge frequencies had a relatively smaller extent of variations in the values for changing compressor speeds in comparison with those of the simple reduced frequencies defined by Eqs. (16) and (20) below.…”

“…The stage characteristics has been supposed on the basis of some literature survey results as described in Yamaguchi [10,11] particularly in the zones of the stalled flow and the reversed flow where consistent and systematic information are rather few. The identical stage characteristics were employed for all the stages and for all the compressor speeds in the present analyses.…”

“…For example, some examples of surge loops and time histories in Figs. 5 through to 8 in Yamaguchi [10] and the phenomena of insufficient surge recovery in a nine-stage compressor in Figs.10(c) and 11(c) in Yamaguchi [11] are considered to be the situations.…”

“…It is usually considered that the surge frequencies in compressor surges are related closely with the acoustical resonance frequencies of the air column in the compressor-duct system. According to some examples analyzed by the author (Yamaguchi [9][10][11]), however, the surge frequencies are not necessarily the same as the resonance frequencies of the system. Possibly, affected by the large amplitude of the surge oscillations and various influential factors, the surge frequencies could deviate much from the acoustical resonance frequencies which assume infinitesimally small perturbations.…”

“…In multi-stage situations of the compressors, in addition to the global influence by the pressure ratio, stage-wise distributions of working conditions could affect the phenomena, also. For example, differences of working conditions among the stages for far off-design speeds in multi-stage compressors could affect the phenomena (Yamaguchi [11]). Higher harmonic mode surge might happen to occur, though very locally, depending on the duct geometrical conditions and the relative locations of the compressor in the flow-path layout.…”