Tip clearance influence in CFD calculations and optimization of a centrifugal compressor stage through CFD methods

Abstract

This paper presents a study on a centrifugal compressor stage aerodynamics. The influence of the blade tip clearance on performances of the centrifugal impeller and also on the diffuser is taken into consideration for the overall optimization process. Also a stress analysis has been carried out to investigate the stresses and strains of the blade. The impeller was designed for a pressure ratio of 4:1, a mass flow of 8.1 kg/s at 22 000 rpm. Three cases have been studied: first without a tip clearance, the second one with tip clearance and the third case which studies an optimized geometry for the vaned diffusers. Through a designer driven optimization process, the recirculation zone that appears in the diffuser was reduced by half. Following the numerical analysis some differences were noted between the three cases in terms of both global results and particular flow details. One of the main differences is given by the power consumed by the impeller. Due to the elimination of the tip clearance (shrouded impeller), the power consumed by the impeller was reduced by 72 kW and the efficiency increased by 2.2%. In the case of diffusers analysis, was noticed an improvement in stage efficiency of 8.2%.