Effect of Circumferential Grooves and Tip Recess on Stall Characteristics of Transonic Axial Compressor Rotor

Abstract

In the modern day gas turbine engine compressors have higher loading per stage and hence reduced stability range. Although the optimum performance is located close to stability limit but the flow instabilities arises due to the sudden change in operating conditions may lead to stall. Therefore a sufficient stall margin must be maintained to avoid such situations. The casing and tip treatments offer the stall margin improvement. In the present paper the effects of tip recess, circumferential grooves and combined model on the stall characteristics of a transonic axial flow compressor rotor (NASA rotor 37) has been investigated. The tip recess depth is equivalent to nominal clearance gap of 0.0356 cm. For the second model the six grooves were placed in casing from 20% to 80% of the blade tip chord. The depth of groove is three times of the width (0.4 cm). The separation between the grooves is half of the width. The maximum improvement in stall margin (62.45%) is achieved with circumferential grooves coupled with tip recess with some performance penalties. However the improvement with combined model is marginal as compared to only circumferential grooves model. The stall margin enhancement with tip recess model is 15.50% which is relatively lower than the other two models but with less performance penalties.