Effect of Tip Clearance in a Low Speed Centrifugal Compressor

Abstract

Effect of tip clearance on flow field of a low speed centrifugal compressor is presented. Computational study of centrifugal compressor is carried out using structured multi block grid with fine grid in the tip clearance region. Results are obtained with finite volume method upwind scheme using TASCflow software. Centrifugal compressor impeller with four values of clearances i.e., τ = 0%, 1%, 2% and 5% of blade height at trailing edge are examined at five flow coefficients 0.28, 0.34, 0.42 (design value), 0.48 and 0.52. The effect of tip clearance on total pressure coefficient and static pressure coefficient from inlet to outlet of the compressor is analysed at flow coefficient of 0.52. The drop in static pressure coefficient and total pressure coefficient with increase in tip clearance is found to be high at the tip of the blade due to high pressure fluid leakage at the tip of the blade. The static pressure coefficient, total pressure coefficient and tangential velocity variation at outlet are presented at flow coefficient of 0.52. Mass averaged performance graph show the reduction of performance with tip clearance. Total pressure coefficient contours are analysed in five meridional locations at φ = 0.42. Relative velocity vectors are plotted at five meridional locations for τ = 5% at φ = 0.48. Relative flow angle contours are presented at five meridional locations for all clearances at φ = 0.28.