NUMERICAL INVESTIGATION OF THE INTERACTION OF A CIRCUMFERENTIAL GROOVE CASING TREATMENT AND NEAR-TIP MODIFICATIONS FOR A HIGHLY-LOADED LOW-SPEED ROTOR UNDER THE INFLUENCE OF DOUBLE LEAKAGE

Abstract In [1], Eckel et al. proposed using a convex-profiled pressure side region close to the tip, known as belly, as an effective method of extending the operating range of low-speed axial compressor rotors. In the literature, circumferential grooves are another well-described technique for improving the stable working range of a compressor rotor. No research has been conducted to date to determine which modification is more effective and how they interact when used together. This paper numerically investigates the influence of circumferential casing grooves and near tip modifications on the flow field in the tip region of a highly-loaded, low-speed axial compressor rotor. The simulated rotor consists of a hybrid blade configuration with a tandem profile in the mid-span region and single blade profiles near the endwalls. The aim of the numerical analysis is to explain the interaction of the secondary flow phenomena when applying the circumferential grooves and the belly geometries. It is shown that a circumferential groove can further increase the operating range for all belly configurations when positioned axially correctly. In this respect, equalization of the near-casing deceleration in the circumferential direction leads to an extension of the stall margin with both modifications. In general, the groove and belly should be positioned where the tip leakage vortex meets the pressure side of the adjacent blade. If using only one modification, the belly appears better suited for ensuring an extension of the operating range while maintaining high efficiencies.