Computational Analysis of Effect of Circumferential Groove Casing Treatment With Different Axial Coverage Over Rotor Blade Tip Chord on the Performance of a Transonic Axial Compressor Stage

Previous studies on circumferential groove casing treatments have shown that the effectiveness of casing Grooves highly depends on their axial location over blade tip. The present work aims to study the flow behavior and its impact on the performance of the compressor stage when the casing treatment grooves are placed to provide different axial coverage over rotor chord in each case. Geometry of a transonic compressor stage was modeled for this study. Flow field solutions for this model with smooth casing wall were obtained by solving steady state 3-D Reynolds-Averaged Navier-Stokes equations for three different grids to prove the grid independence of the solutions. Results obtained with the intermediate grid density were used as the baseline results to compare with results of casing treatment geometries. The basic casing treatment geometry has 10 circumferential groves of width 4mm, depth 16mm and axial spacing of 2mm between each groove. This casing treatment geometry was superimposed over the rotor domain with the grooves extending axially over the entire axial chord (58mm) of rotor blade tip and flow field solutions were again obtained. After that, for each case the grooves are removed from the rear side and axial coverage is shortened. Flow solutions for various axial coverage and hence for various number of grooves are thus obtained and compared. These results depict improvement in the operating range when compared to the Base-line results. Results also exhibit that as the grooves from the rear end are removed gradually, recovery in the overall efficiency is seen in compressor performance. Post processing of the flow solutions confirms the trend and shows that the grooves in the rear of the chord are almost idle not providing sufficient flow to pass over from pressure surface to suction surface of the blade and hence contributing very less towards performance enhancement.