Effect of lean on performance of an axial compressor rotor with circumferential casing grooves

Axial Compressors used in gas turbine engines are susceptible to stall. This phenomenon is more prevalent in aero gas turbine engines, due to requirement of varied operating conditions based on flight envelop. There are a number of methodologies in use for increasing stall margin of compressor and hence the operating range of the engines. One of such most widely used techniques is circumferential casing grooves. Circumferential casing grooves helps in increasing stall limit, but generally with a penalty on efficiency, by breaking down tip vortices. In order to increase the efficiency and pressure ratio, rotor blades are designed to reduce secondary losses. Designing blades with lean and sweep are one of the techniques to reduce secondary flow losses. A number of literatures are available in public domain, giving detailed understanding of effect of circumferential groove and 3D blade features like lean and sweep. In this current work, an effort is made to understand the interaction effect of lean and circumferential grooves, using computational fluid dynamics (CFD). In order to use CFD as a tool to understand flow physics and predict performance, a thorough validation is carried out. CFD results, both performance parameters as well as span-wise distribution of different flow variables, are compared with available experimental data of NASA Rotor 37. Current investigation starts with generation of a baseline rotor, having no lean and no sweep. The rotor geometry is created using hub and tip profiles of NASA Rotor 37. Flow path used for this rotor is same as that of NASA Rotor 37. The profiles are stacked along a radial line through the center of gravities of the profiles. This has resulted in desired geometry, without lean and sweep. Slight modification is made in terms of stagger angle of the tip profiles, to get comparable performance as NASA Rotor 37. Five circumferential casing grooves between leading edge and trailing edge of the rotor are created as per industry standard. Meshing and modeling are done according to the best practices developed while validating CFD methodology. Analyses of baseline rotor are carried out from choke to stall, with solid shroud as well as grooved shroud. Grooves shroud has resulted in higher stall margin, as expected. In order to study the interaction effect of casing grooves with lean, a number of different rotors geometries are generated with varying amount of lean as well as different span location from where lean starts. Results obtained from these numerical simulations are presented in this paper. Performance and flow features are compared with baseline rotor, with and without grooves, in an attempt to understand global as well as localized effect of interaction between casing grooves and lean.