The Effect Of Tip Injection On The Compressor Stability

Fan/compressor is one of the aero engine’s most important parts, whose stability directlyinfluences aero engine stability. In order to meet up-to-date aero craft flight target such asunconventional flexibility, supersonic cruise, a higher thrust-to-weight ratio needs to be increasedwhile fuel rate needs to be decreased, which requests higher pressure rise and loading per stage for thefan/compressor. Therefore, these demands make it difficult to ensure their aerodynamic stability. Themethods to enlarge fan/compressor stable margin such as using air injection and casing treatmentcome to appearance. Thoroughly understanding the compressor especially stall inception isindispensable if effective execution of these methods needs to be achieved.In order to explore axial compressor flow instability mechanism, and be ready for micro airinjection experiment on the compressor stability. Based on the turning of through compressorcharacteristic and stage characteristic, the the first stage stator and the second stage stator outlet andpassage flow field and blade tip leakage flow on top of the first stage rotor development are analyzed,and the result is that compressor stall has close relation with boundary layer separation of the blade tipsuction surface; according to the research of the stall inception, the compressor rotating stall isincepted by modal wave, which appears in the blade tip of the first stage. With all these in condition,injection system should be set in the outer casing of the compressor inlet upstream.In the uniform inflow, the effect of injection parameter such as the injection mass flow, injectornumber, circumference configuration of the injection system on the compressor stall margin wasstudied. The results indicate: under the condition that not less than four injectors are equally spacedcircumferentially, injection angle is a certain number to the counter rotation and momentum perinjector is as large as possible, the enhancement stability effect of the injection arrives at the most;under the guide of the parametric investigation, the mechanism of the micro injection enhancing thecompressor stability could be gotten, because the micro injection suppresses the modal wavedevelopment to the rotating stall from the facet of frequency, magnitude and axial structure. Based onthis, a physical model explaining how the micro injection enhance the compressor stability is putforward. At the same time, the micro injection delays tip leakage flow movements toward the rotorleading edge face and ameliorate the rotor tip loading.In order to strengthen the compressor ability against inlet distortion, so that it can work normallyadverse inlet flow field, the investigation to test whether the micro injection improves compressor stability under the condition of inlet distortion has high value for practical purpose. The researchresults indicate under the condition of the uniform inflow, the reason why the micro injectionenhancement the compressor stability under the condition of the inlet distortion is that the microinjection suppresses the modal wave development towards the rotating stall. When the total pressuredistortion style is different, the effect of micro injection enhancing compressor stability is different,too. For example, that effect isn’t obvious for the pure radial total pressure inlet distortion, however, itis obvious for the pure circumference total pressure inlet distortion. At the condition of the totalpressure inlet distortion, the enhancement with equally spaced circumference is the best, the effect ofenhancement stability for injection pooling in the low pressure area is better than that in the highpressure area.Steady tip injection on an isolated axial flow compressor, NASA Rotor37, has been studied inthe paper by using the method of numerical simulation. At first, the compressor stall reason can befound at the100%and50%designed rotating speed. At the designed rotating speed, the interactionbetween the shock wave and tip leakage flow leads to the blockage in the blade tip area, which resultsin the stall finally. Second, the effect of micro injection on the compressor stability at the two rotatingspeed are studied. The results indicate at the designed rotating speed, even if the injection is at thechoked condition, the effect of steady injection on the compressor stability is little; at the50%designed rotating speed, when injection mass flow reaches a certain value, that effect is obvious.