An investigation of the three-dimensional flow field in a centrifugal compressor

John Robert Fagan, Purdue University

Abstract

A series of experiments was performed to provide three-dimensional flow field data in centrifugal compressor passages and to describe the characteristic flow phenomena at the point of incipient rotating stall. These experiments entailed the acquisition and analysis of one-dimensional LDV data in the impeller passages of the Purdue Research Centrifugal Compressor at two compressor operating points: (1) the design operating point and (2) the incipient rotating stall operating point. Additionally, the nature of compressor rotating stall was quantified by the acquisition and analysis of unsteady pressure data at the impeller inlet and exit. Finally, predictions at the design operating point from contemporary internal flow models were used for comparison with the LDV data. The LDV data taken at both operating points show the traditional jet-wake structure observed in many centrifugal compressors. At the design point, the wake was observed along the shroud 70% of the length from the pressure to suction surface. At the incipient stall point, the wake was located in the shroud suction corner. The unsteady pressure data show three distinct modes of rotating stall in the compressor depending upon the mass flow rate. One mode is characterized by two stall patterns rotating concurrently with relative rotational speed below 15% of the impeller rotational speed. This mode occurs at the highest mass flow rate and is strongest at the impeller inlet. The other two rotating stall modes occur at reduced mass flow rates and are characterized by single rotating stall patterns. The patterns in both modes rotate with relative speeds exceeding 90% of the impeller rotational speed, with the patterns strongest at the diffuser inlet. The inviscid flow model did not successfully predict the compressor flow field. The viscous flow model achieved better success. It predicted the major phenomena in the flow field, specifically the wake structure near the end of the passage. However, the viscous model shows poor correlation with the data, predicting that the wake was located in the shroud suction corner different from the LDV results at the design operating point.

Degree

Ph.D.

Advisors

Fleeter, Purdue University.

Subject Area

Mechanical engineering

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