Effects of 3D Aerofoil Tip Clearance Variation on a 4-Stage Low Speed Compressor

The aerodynamic performance of turbomachinery airfoils and therefore the overall efficiency of an engine are strongly dependent on the design of the near end wall sections of blades and vanes. In addition, good compressor stability can only be achieved if the running clearance is as small as allowed for save operation. In the engine the radial gap varies in size due to thermal effects and deterioration as well as transient maneuvers. Since the width of the running clearance can hardly be reduced, a new aerofoil sectional design for cantilevered vanes has been introduced to improve compressor stability over its whole range of operation. The baseline design and the new improved concept have been tested and analyzed for different clearance widths (TC1…TC3) on the rotor blades and cantilevered stator vanes. A baseline configuration featuring two-dimensional airfoils has been used as a datum to develop a more advanced design applying sweep and dihedral at the stacking axes. The running clearance on rotors and the radial gap on cantilevered stators were increased in three steps. Both numerical and experimental investigations had been carried out to verify the effect of variable running clearances on modified end wall sections. Experimental and numerical investigations have shown the effect of bow and sweep within this low speed application does not fully support the common theory of unloaded end wall sections as discussed in various publications. For the 2D blade design the common theory has been proven by both numerical and experimental evaluations. The 3D blade design configuration (BUILD IX) features a significant difference in efficiency sensitivity due to tip clearance width variation, whereas numerical prediction suggested improved compressor performance and stability. Measurements has shown higher losses at this configuration.