Performance Evaluation of Tandem Bladed Centrifugal Compressor

Abstract

A tandem-bladed centrifugal compressor which may have better performance than the conventional designs has not yet been studied for its potential turbocharger application. In addition, no numerical study of the entire stage (including tandem impeller and volute) has been performed to fully exploit the benefits of such design with variation in axial clearance levels, circumferential clocking fractions, blade geometries/angles, number of inducer blades and the thickness of inducer blades. This paper presents a thorough experimental and numerical study on the performance of a moderate pressure ratio, unshrouded, tandem-bladed centrifugal compressor in comparison to a conventional compressor of commercial use in china for turbocharger application. The characteristics of a tandem compressor are investigated and compared for various parameters. Conventional impeller was first modified into tandem-bladed design but with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison. The tandem design was further modified and investigated by (1) narrowing down the meridional gas passage, (2) using straight or concave leading edge of exducer, (3) reducing the thickness and (4) the number of inducer blades. CFD and experimental results were found to be in good agreement. The study reveals a shift of surge point towards lower mass flow rate in all cases of tandem designs. A maximum of 25% increase in the range of operation is observed. All in all there is little influence of the different circumferential clocking fractions and axial spacings of the inducer. Computational investigations of a modified tandem compressor with 20% reduction in inducer thickness have shown better performance than the conventional design. Use of fourteen inducer blades with reduced blade thickness can further enhance the performance.