Influence of Compressor Deterioration on Engine Dynamic Behavior and Transient Stall-Margin

Abstract

This paper presents an experimental and analytical investigation of compressor stability assessment during engine transient operation. A 2-dimensional, linear, compressible, state-space analysis of stall-inception (Feulner et al. (1996)) was modified to account for engine transients and deterioration, with the latter modeled as increased tip-clearance and flow blockage. Experiments were performed on large commercial aircraft engines in both undeteriorated and deteriorated states. Unsteady measurements of pressure in these test engines during rapid accelerations revealed the growth of pre-stall disturbances, which rotate at rotor speed and at approximately half rotor speed. These disturbances are stronger in deteriorated engines. The model showed that the signal at shaft speed was the first compressible system mode, whose frequency is near shaft speed, excited by geometric nonuniformities. The computed behavior of this mode during throttle transients closely matched engine data. The signal increased in strength as stall was approached and as the engine deteriorated. This work firmly establishes the connection between observed signals in the these engines and first principles stability models.

Degradation of gas turbine performance in natural gas service

“…4). The reduction in flow is observed by numerous authors (Spakovszky et al, 1999;Millsaps et al, 2004). However, the pressure ratio-flow relationship of the gas turbine compressor remains unchanged (because it is determined by the turbine section), but the engine will have to run faster, and the compressor will consume more power for any point on the pressure-flow line once it deteriorates.…”

“…Spakovszky et al (1999) as well as Khalid et al (1998) relate increased rotor clearances to an increase in flow blockage, thus reduced compressor flow capacity. We find that the same level of compressor flow blockage leads to more power degradation in a two shaft engine than in a single shaft engine.…”

“…While in the new machine all stages were working at their optimum efficiency point at design surge margins, the degradation will force all stages after the first one to work at off optimum operating conditions, thus reducing surge or stall margins and efficiency (Kurz et al, 2008;Brun et al, 2005;Spakovszky et al, 1999). This will not only lower the overall efficiency and the pressure ratio that can be achieved, but also the operating range.…”

“…Changes in surface quality and airfoil geometry reduce efficiency and work capability of the stage. Increased clearances reduce surge margin, reduce the efficiency, cause a reduction in stage work, and reduce the compressor flow capacity (Kurz and Brun, 2001;Spakovszky et al, 1999;Graf et al, 1998;Smith and Cumpsty, 1984;Frith, 1992).…”

Gas Turbine Optimum Arrangement for Process Plants

“…In extensive studies [8,10] the compressor section of gas turbine performance was deteriorated by spraying salt water in the inlet. The deposits caused increased the surface roughness on the compressor foils (majority of deposits occurs on the first stage and become insignificant after the fourth stage).…”