Computational study of tip clearance effects in a centrifugal compressor

Computational study of tip clearance effects in a low speed centrifugal compressor is carried out using structured multi block grid with fine grid in the tip clearance region. The flow through the centrifugal compressor is analyzed with finite volume method upwind scheme using TASCflow software. Standard k-epsilon turbulence model is used for obtaining the solution. Centrifugal compressor impeller with four values of clearances i.e., 0%, 1%, 2% and 5% of blade height are examined at three flow coefficients 0.28, 0.34 (design value) and 0.42. The effect of tip clearance on total pressure coefficient and static pressure coefficient from inlet to outlet of the compressor is analyzed. Total pressure, relative flow angle contours and velocity vectors were shown on two meridional planes. Static pressure distribution on the surface of the blade at flow coefficient 0.42 for all tip clearances was plotted. 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. Shifting of reduced maximum value of nondimensional tangential velocity towards hub at exit of impeller with increase in clearance is observed. The reduction of blade loading near the tip increases with tip clearance.