Experimental investigations of micro air injection to control rotating stall

Abstract

Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be an effective method to delay the inception of rotating stall in a low speed axial compressor. Considering the practical application a new type of micro injector was designed and described in this paper, which was imbedded in the casing and could be moved along the chord. In order to verify its feasibility to other cases, such as high subsonic axial compressor or centrifugal compressor, some other cases have been studied. Experimental results of the same low speed axial compressor showed that the new injector could possess many other advantages besides successfully stabilizing the compressor. Experiments performed on a high subsonic axial compressor confirmed the effectiveness of micro air injection when the relative velocity at the blade tip is high subsonic. Meanwhile in order to explore its feasibility in centrifugal compressor, a similar micro injector was designed and tested on a low speed centrifugal compressor with vaned diffuser. The injected mass flow was a bit larger than that used in axial compressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugal compressor.

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

“…The injection results in the reduced strength of the vortex oscillations, smaller vortices, and reduced total pressure loss. In an axial compressor, the optimum location for the injection is at the rotor blade leading edge, or upstream of it [170,176] and an injector throat height lower than four times the rotor tip clearance is recommended [170]. In this optimum location, the injection acts on the tip leakage flow delaying the onset of stall.…”

“…. +1.5% +20% [200] 2012 Injection nozzle CC 2-11% ±0% +20% [176] 2007 Injection nozzle AC 0.15% +9% [176] 2007 Injection nozzle CC 0.9% +10% [201] 2005 Injection nozzle CC 0.9-4.6% ±0% ±0% [202] 2004 Injection nozzle CC 0.5% +25% [178] 2003 Injection nozzle CC 0.9% −1% +15% [178] 2003 Bleed control tube CC −5.5% +56%…”

“…Nie et al [176] achieved a 10% increase in surge margin by implementing the injection in the impeller inducer. Figure 12 shows a schematic view of the injection nozzle in the impeller inducer, where the high-momentum fluid is circulated from, e.g., the compressor outlet.…”

“…In the literature, the reported recirculation flow rate through the recirculation slot of a self-circulating casing treatment varied from 0.15% [176] to an extremely high 80% [183] of the main mass flow rate in the literature. Zhu et al [174] distinguished a linear correlation between the injection mass flow rate and stall margin improvement from numerical results.…”

Numerical investigation of rotating stall in centrifugal compressor with vaned and vaneless diffuser

“…When the injector is moved away from the impeller blades leading edge, the pressure losses are decreased but the surge margin is decreased also. Nie et al [8] made an experimental investigation about using air injection in a high speed centrifugal compressor. Results showed that the best location to inject air is at the upstream of the impeller blades tip because the flow separation is better controlled and minimized at the impeller inlet.…”