Passive flow control using slots is a well-known method to improve the stall margin of an axial flow compressor. This paper numerically investigates the effect of axially skewed slots on the performance of a high speed single stage subsonic axial flow compressor. NACA 65 series blade profile of chord and span, 85 and 106 mm, respectively, is generated and simulated using ANSYS software. The axial flow compressor consists of 21 rotor blades with a tip clearance of 0.5 mm. A total pressure ratio of 1.22 is obtained at 12000 rpm. The present numerical results are validated with the experimental data by using three different turbulence models, namely, SST, k-ω and k-ε. The closest matching is observed with the SST turbulence model, hence, it is chosen for the present numerical studies. Subsequently, grid independence study is carried out at different number of grid elements, such as, 2, 6, 8, 10, 12 and 16 lakhs. For 10 and 12 lakhs grid elements, the difference in pressure rise and compressor efficiency is about 0.06% and 0.29%, respectively. Therefore, present studies are carried out at 10 lakhs grid elements. A parametric study is carried out to investigate the influence of length, depth and skewness of the slot on the performance of the compressor. The slot width and center-to-center distance between the successive slots are 4 and 7 mm, respectively. In the present studies, different slot lengths are used, namely, large (slot length from 0 to 100% of axial chord), medium (20 to 100% of axial chord) and short slot (40 to 100% of axial chord). The slot depths are varied to 5, 7 and 10 mm, whereas, different skew angles, such as, 0o, 30o and 60o are used to unravel the compressor performance. For different slot lengths, the best performance is achieved for the medium slot which is placed from 20 to 100% of axial chord. The improvement in stall margin is 9%, whereas, pressure rise is mildly enhanced by 0.2%. The stall margin improvements for the large and short slots are, 4.3% and 6.7%, respectively. It is anticipated that the performance improvement of axial flow compressor attributes to the incorporation of the slots which forms recirculating vortices that exchanges their momentum with the retarding boundary layer flow. Subsequent simulations are underway to demonstrate the role of depth and skew angle of the slot on the compressor performance. Along with the quantification of compressor performance, the present studies will also focus on modifications in the flow characteristics near the tip region due to incorporation of the slots.

A Parametric Study on the Effect of Casing Treatment Slots on Performance Enhancement of a Single Stage Axial Flow Compressor

Paper Proceedings: https://asmedigitalcollection.asme.org/GTINDIA/GTINDIA2021/volume/85536

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