Abstract
Aspiration in an axial compressor is normally regarded as sucking out the low momentum boundary layer from blade suction surface, thus lowering the chances of flow separation and consequently that of stall under off-design operation. However, the suction mass flow does not take part in useful work and leads to loss of engine power output. This paper deals with a new concept of natural aspiration to energize blade suction surface boundary layer by injecting some fluid from pressure to suction side through a part span slot on the blade. The energized boundary layer has lesser tendency to separate, thus enhancing stall margin. Numerical simulations were carried out to study the effect of aspiration slot location and geometry on the performance and stall margin of a transonic axial compressor rotor. The computational results without aspiration slot were in fair agreement with the published experimental data. The modified rotor, with part span aspiration, showed ~3.2% improvement in stall margin at design rotational speed. The pressure ratio and efficiency of the aspirated rotor dropped by ~1.42% and ~2.0%, respectively, whereas the structural analysis did not indicate any adverse effect on the blade stress distribution in the presence of aspiration slot.
Highlights
Axial flow compressors offer high air mass flow rate capacity with small frontal area, which is advantageous for aeroengines [1]
The choice is to use transonic axial compressor stages owing to their higher pressure ratio capability compared to subsonic stages and higher efficiency compared to fully supersonic stages
Transonic Axial Compressor The NASA 37 transonic axial flow compressor rotor [12] was selected for the present study
Summary
Axial flow compressors offer high air mass flow rate capacity with small frontal area, which is advantageous for aeroengines [1]. Experimental investigation on a 1.6 pressure ratio transonic axial compressor stage, demonstrating the application of boundary layer aspiration on the rotor and stator suction surfaces, has been reported by Schuler et al [2]. A three-stage, counterrotating compressor was designed by Freedman [7] to investigate the aspiration technique comprising suction on the surface of the blades and end walls to keep the boundary layer attached under high loading conditions, reducing losses. A low tip speed (213 m/s), aspirated fan stage of 1.5 : 1 pressure ratio was experimentally investigated by Kerrebrock [9] to increase the work per blade row through boundary layer control within the flow path. The forced boundary layer suction is beneficial in improving the compressor performance in terms of reduced flow separation, increased blade loading, and stable operating range. The simulation results are presented in terms of global compressor performance and detailed flow behavior through the blade passages
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