The Experimental Study of Matching Between Centrifugal Compressor Impeller and Diffuser

The centrifugal compressor for a marine use turbocharger with its design pressure ratio of 3.2 was tested with a vaneless diffuser and various vaned diffusers. Vaned diffusers were chosen to cover impeller operating range as broad as possible. The analysis of the static pressure ratio in the impeller and the diffusing system — consists of the diffuser and scroll — showed that there were four possible combinations of characteristics of impeller pressure ratio and that of diffusing system pressure ratio.The flow rate, QP, where the impeller achieved maximum static pressure ratio was the critical flow rate determined surge flow rate of the centrifugal compressor. In order to operate the compressor less than QP, the diffusing system whose pressure recovery factor was steep negative slope near QP was needed. Using the diffuser throat area less than a certain value, the compressor efficiency deteriorated, however the compressor stage pressure ratio was almost constant. In this study, the compressor by reducing the diffuser throat area could be operated at the flow rate less than 40% of its design flow rate. Analysis of the pressure ratio in the impeller and diffusing systems at design and off design speeds showed that the irregularities in surge line occurred when the component which controlled the negative slope on the compressor stage pressure ratio changed.Copyright © 1997 by ASME