Effect of Lean on Performance of an Axial Compressor Rotor with Casing Grooves
Shraman N Goswami, Honeywell Technology Solutions, Bangalore, India
M. Govardhan, Dept. of Mechanical Engineering, IIT Madras, Chennai, India
Long Abstract
Introduction
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 the flight envelope. There are a number of methodologies in use for increasing stall margin of compressor and hence the operating ranges of the engines. One of such most widely used techniques is Circumferential Casing Grooves. Circumferential Casing Grooves helps in increasing the stall limit, but generally with a penalty on efficiency, by breaking down tip vortices. In order to increase the efficiency and pressure ratio, the rotor blades are designed to reduce secondary flow losses. Designing blades with Sweep and Lean are some of such techniques to reduce secondary flow losses. A number of literatures are available in public domain, giving detailed understanding of effect of Circumferential Casing Grooves and 3D blade features, like Sweep and Lean. In this work, an effort is made to understand the interaction effect of Lean with Circumferential Grooves, using Computational Fluid Dynamics (CFD).
1. Methods
The current numerical investigation starts with generation of a baseline rotor, without sweep and lean. The baseline rotor is created by using hub and tip profiles of NASA Rotor 37 and stacking the profiles along a radial line through their center of gravities. This has resulted in a rotor without sweep or lean. Slight modifications are done to the tip profile, in terms of stagger angle, to get comparable performance with respect to NASA Rotor37. Circumferential Casing Grooves, with five grooves between leading and trailing edge, are created as per industry standards. Meshing and modeling are done according to the best practices developed while validating CFD methodology. It is to be noted that the casing grooves and the main flow domain are having one to one mesh connectivity, in order to avoid any numerical losses due to interface interpolations. This is considered very critical in this work, as the vortices from the tip is expected to have a strong interaction with grooves and a higher gradients of flow variables will prevail at that region. Interpolation in this region can give riise to loss of valuable flow information. Analysis of baseline rotor with solid shroud and casing grooves are carried out from choke to stall. From the numerical results it is observed that an increase in stall margin is resulted by introduction of casing grooves, as expected. In order to study the interaction effect of casing grooves with lean, a number of rotor geometries are generated with varying amount of lean. The span location where the lean starts is also changed to understand the localized and global effect of this blade design feature. Results obtained from numerical simulations of these geometries are presented in this paper. The performance and flow features are compared with respect to baseline rotor, with and without circumferential grooves, in an attempt to understand the underlying flow physics [1][2].
References
[1] Breugalmans F., “Investigation of Dihedral Effects in Compressor Cascades”, AGARD-CP-421, 1987.
[2] Sasaki T, Breugalmans F., “Comparison of Sweep and Dihedral Effects on Compressor Performance”, ASME GT 2, 1997.