Experimental Investigation on a Centrifugal Compressor by means of squealer tips

Centrifugal compressors are suitable for low specific speed, high pressure ratio and low mass flow applications. They are used in large refrigeration units, petro-chemical plants, and power plants for small aircraft and helicopters. Performance of the centrifugal compressor is slightly lower than that of the axial type. However, a much higher pressure ratio-per stage, single piece impeller and a wider range of stable operation are some of the attractive aspects of this type of compressor. The tip leakage flow has a dominant effect on the performance of a compressor, as the relative tip clearance is high. The objective of the present investigation is to explore the possibility of using squealer tip to improve the performance of centrifugal compressor. This is achieved by the testing the compressor with four different tip configurations, namely, suction side squealer, pressure side squealer, squealers on both suction and pressure sides and solid tip by filling up the space between squealers. The following experiments are carried out to achieve the objective: measurement of performance of the compressor with squealers on suction side, pressure side, on both suction and pressure sides and solid tip. From these measurements, characteristics such as the energy co-efficient and efficiency against flow co-efficient are obtained. Impeller exit traverse with a pre-calibrated five hole probe for all configuration at three different flow coefficients are tested. From the present investigation, it is concluded that pressure side squealer tip has beneficial effects in increasing energy coefficient and efficiency of compressor. In addition, mass averaged total and static pressures obtained from the probe traverses are improved. Suction side squealer tip has comparable beneficial effect on the energy coefficient and efficiency.