High-speed high-pressure ratio compressor surge is a transient breakdown in compression accompanied by an abrupt momentary reversal of gas flow. It commonly exists in dynamic type turbo compressors, particularly in the axial compressor of modern aero-engines. By Newton’s Laws of Motion, a force is needed to change the state of any motion. So what is the force that can cause such a dramatic motion as surge? What exactly triggers it, and how do we quantify the transient surge phenomenon? This paper attempts to answer these questions and discuss the transient dynamics of surge at its initial stage. It has generally been accepted that surge is precipitated by the onset of a rotating spike or stall, not only for low speed but for high-speed compressors too. The state of dynamic surge modeling today is best exemplified by the “Greitzer-Moore” model. However, it fails to incorporate the key elements of the transient nature of a surge inception: the extremely short time duration on millisecond scale and the shock wave presence observed experimentally. An indirect approach is taken in this paper to address the transient dynamics of stall and surge by using an analogy to the shock tube. The link is established based on observations that instant zero net through flow inside stalled cascade cell triggers stall/surge. The results from the analogy reveal that surge initiation simultaneously generates a pair of non-linear compression and expansion waves (CW & EW) and induced reverse fluid flow (IRFF). The dynamic forces for instant flow reversal are the pushing force of upstream propagating CW and the pulling force from downstream travelling EW. Surge Rules are deduced and then compared with experimental findings by previous researchers with good agreements. Moreover, the strength of the transient post-surge components, CW, EW and IRFF, can be estimated analytically or numerically by the shock tube theory from known pre-surge conditions and routes to surge.
This paper is a continuing work from one author on the same topic of the transient aerodynamics during compressor stall/surge using a shock tube analogy by Huang [1, 2]. As observed by Mazzawy [3] for the high-speed high-pressure (HSHP) ratio compressors of the modern aero-engines, surge is an event characterized with the stoppage and reversal of engine flow within a matter of milliseconds. This large flow transient is accomplished through a pair of internally generated shock waves and expansion waves of high strength. The final results are often dramatic with a loud bang followed by the spewing out of flames from both the engine intake and exhaust, potentially damaging to the engine structure [3]. It has been demonstrated in the previous investigations by Marshall [4] and Huang [2] that the transient flow reversal phase of a surge cycle can be approximated by the shock tube analogy in understanding its generation mechanism and correlating the shock wave strength as a function of the pre-surge compressor pressure ratio. Kurkov [5] and Evans [8] used a guillotine analogy to estimate the inlet overpressure associated with the sudden flow stoppage associated with surge. This paper will expand the progressive surge model established by the shock tube analogy in [2] by including the dynamic effect of airflow stoppage using an “integrated-flow” sequential guillotine/shock tube model. It further investigates the surge formation (characterized by flow reversal) and propagation patterns (characterized by surge shock and expansion waves) after its generation at different locations inside a compressor. Calculations are conducted for a 12-stage compressor using this model under various surge onset stages and compared with previous experimental data [3]. The results demonstrate that the “integrated-flow” model closely replicates the fast moving surge shock wave overpressure from the stall initiation site to the compressor inlet.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.