Analytical Study on Stall Stagnation Boundaries in Axial-Flow Compressor and Duct Systems

Abstract

Stall stagnations in the system of axial-flow compressors and ducts occur in transition from deep surge conditions to decayed or converged stall conditions. The present study is concerned with the boundaries between the deep surges and the stagnation stalls on the basis of analytical results by a code on surge transients analysis and simulation. The fundamental acoustical-geometrical stagnation boundaries were made clear from examinations of the results on a variety of duct configurations coupled with a nine-stage compressor and a single stage fan. The boundary was found to be formed by three parts, i.e., B-and A-boundaries, and an intermediate zone. The B-boundary occurs for the suction-duct having a length of about a quarter of the wave-length of the first resonance in the case of very short and fat plenum-type delivery duct. On the other hand, the A-boundary occurs for the long and narrow duct-type delivery flow-path having a length about a fifth of the wavelength and relatively small sectional area in the case of short and narrow suction ducts. In addition to this, the reduced surge-cycle frequencies with respect to the duct lengths are observed to have respective limiting values at the stagnation boundaries. The reduced frequency for the B-boundary is related with a limiting value of the Greitzer's B parameter. The tendency and the characteristic features of the related flow behaviors in the neighborhood of the boundaries were also made clearer.

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

“…Five compressors were studied in the present study including a single stage compressor, Comp11, and a nine-stage one, Comp19, which have been employed in the previous study (Yamaguchi [9,10]), and three more ones, Comp12, Comp13, and Comp15 having two, three and five stages, respectively. The respective major quantities are given in Table 1.…”

“…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.…”

“…The data are complemented by substitution of additional data on Comp12, 13, and 15 at 10000rpm and Comp11 at 15000-6000rpn to the existing ones on Comp19 and Comp11 at 10000rpm (Yamaguchi [9,10]). …”

“…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.…”

“…For the purpose, first of all, a number of case studies have been conducted to study the effects of the numbers of stages and the compressor speeds on the behaviors of the stall stagnation boundaries in addition to those in the preceding reports (Yamaguchi [9,10]). Next, a new reduced frequency describing the essential surge process is proposed.…”