Investigation of Unsteady Compressor Flow Structure With Tip Injection Using Particle Image Velocimetry

Abstract

Fluid injection at the tip of highly loaded compressor rotors is known to be very effective in suppressing the onset of rotating stall and eventually compressor instability. To understand the effects of tip injection, the flow field at the tip region of a transonic compressor rotor with and without fluid injection was investigated in this paper. Using results acquired by phase-locked PIV measurements as well as the static pressure field obtained by fast response pressure transducers, the unsteady interaction between the injection jet and the rotor could be described thoroughly. Both, an influence of the rotor’s flow field on the jet as well of the jet on the rotor was clearly visible. Since unsteady inflow conditions to the front rotor in the relative frame of reference were imposed by the injection jets, the rotor’s unsteady response was investigated by inspection of the position of the tip leakage vortex trajectory. It could be shown that due to a short time for the flow to adapt at the rotor’s leading edge, its position didn’t change distinctly. Because a significantly longer time was needed for the overall passage flow to adapt, it was concluded that this causes the beneficial effect of tip injection.

Mechanism study of performance enhancement in a subsonic axial flow compressor with recirculating casing treatment

“…Matzgeller et al 20 argued that the unsteady adaption of passage flow to the varying inflow conditions was the main reason for the beneficial effect of tip injection rather than a shift of the tip leakage vortex. The unsteady effect was used to capture the influence of tip injection with a streamline curvature method.…”

“…The stabilizing effect of tip injection can be briefly summarized as the unloading effect, [7][8][9][10][11] the action on TLF or endwall blockage, [12][13][14][15][16][17] and the unsteady effect. [20][21][22][23][24] However, it is difficult to evaluate the influence on compressor efficiency accurately for the tip injection with external air source. The injected air in RCTs is supplied with the compressed air in the compression system, which makes it easier to calculate the influence on the compressor efficiency.…”

The effect of injector size on compressor performance in a transonic axial compressor with discrete tip injection

“…In multistage compressor, tip injection with small amounts of injection flow led to significant radial work redistribution and thus stage rematching which might alter the stability of the stall limiting stage. 7 Matzgeller et al 15 depicted the phenomena of unsteady interactions between the injected jet and the annulus flow by monitoring the position of the tip leakage vortex (TLV). The unsteady effect of discrete tip injection on compressor performance has not been investigated yet.…”