Deterioration of Compressor Performance due to Tip Clearance of Centrifugal Impellers

The authors’ theory on the tip-clearance loss of centrifugal impellers is modified to include variation of gas density in the impeller. Furthermore, a relationship between two empirical parameters in the theory is derived to reduce freedom of adjustment. In order to compare experimental data in the literature with prediction, examination was made regarding accuracy of data and the way to determine the corresponding flow rates at different tip clearances. Fair agreement between data and prediction was observed. These examples demonstrated effect of various parameters on tip clearance loss as follows. The clearance loss of high pressure-ratio compressors is less than that of low pressure-ratio compressors if the tip clearance ratio at the impeller exit is given. The clearance loss becomes smaller as the flow rate is reduced and also at a reduced shaft speed in cases of high pressure-ratio compressors. The equations in the theory clearly show these tendencies.