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

Abstract

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.

Analysis and application of a new type of sweep optimization on cantilevered stators for an industrial multistage axial-flow compressor

“…Fischer et al 10 conducted an experimental investigation to study the strongly bowed stators in a 4-stage high-speed compressor and showed that separation was reduced in the bowed stator vanes and an increase in the stagnation pressure ratio and efficiency. Tschirner et al 11 showed that the effect of bow and sweep within the investigated low-speed compressor did not fully support the common theory of unloaded end-wall sections as discussed in various studies.…”

Hub clearance effect in the design space of the cantilevered stator embedded in a 4-stage low-speed research compressor

“…Montomoli et al 8 calculated the LSRC test rig and showed that the unsteady simulation could reproduce total pressure loss experimentally observed near the hub at the stator exit but not found in the steady simulation. Tschirner et al 9 carried out LSRC test on three kinds of hub clearances (1.8, 3.0, and 4.8 mm, corresponding to 1.79%, 2.98%, and 4.76% span), with the purpose of studying the impact of increased running hub clearance on standard airfoils such as medium loaded stators, and showed that a sensible impact of increased running gaps onto compressor stability. Ju et al 3 studied the cantilevered stator with 1.1% span of hub clearance and gave the evolution of the hub leakage flow at NS operating condition compared with DP.…”