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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.

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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.

This paper is a continuing work from the same authors on the same topic on gas pulsation and noise control using a shunt pulsation trap (SPT) method by Huang [1, 2, 3]. Traditionally, a serial pulsation dampener/muffler, often a reactive type, is connected AFTER the discharge of a positive displacement compressor. It has been demonstrated in the previous experimental investigations that gas pulsations from under-compression (UC) can be as effectively controlled by an alternative scheme - shunt pulsation trap (SPT), which is more compact and tackles the gas pulsations BEFORE the compressor discharge. Two dampening SPT schemes were investigated and compared: using a perforated plate (p-plate) vs. a perforated tube (p-tube). However, the pulsation induced noise is still a challenge with SPT employment alone. The focus of the present paper investigates experimentally the effect of a new dampening scheme - combining a SPT with a nozzle and an integrated absorptive silencer (IAS) to undertake both pulsation and noise problems at source. It is found that an ASME nozzle SPT with IAS scheme has superior noise reduction capability than both the p-tube + IAS scheme and the traditional scheme using premium silencers. Furthermore, the addition of an integrated absorption silencer (IAS) is not suffering as much back pressure drop associated with traditional reaction type silencers and therefore will not affect system efficiency. The integration of absorptive silencer into a nozzle or p-tube based SPT would provide an optimal design choice for size/weight and pulsation/noise reduction and potentials for energy saving for PD compressors operating in UC mode.

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