Jet-wake Flow Research Articles

Study of Internal Flows in a Mixed-Flow Pump Impeller at Various Tip Clearances Using Three-Dimensional Viscous Flow Computations

The complex three-dimensional flow fields in a mixed-flow pump impeller are investigated by applying the incompressible version of Dawes’ Three-Dimensional Navier–Stokes code. The applicability of the code is confirmed by comparison of computations with a variety of experimentally measured jet-wake flow patterns and overall performances at four different tip clearances, including the shrouded case. Based on the computations, the interaction mechanism of secondary flows and the formation of jet-wake flow are discussed. In the case of large tip clearances, the reverse flow caused by tip leakage flow is considered to be the reason for the thickening of the casing boundary layer followed by the deterioration of the whole flow field.

A Blockage Model for Centrifugal Compressor Impellers

This paper presents and discusses the results of an analysis in which the blockage distributions of four impellers were deduced from shroud static pressure measurements. The purpose of the analysis was to provide a means of estimating blockage for the jet-wake flow model for use in impeller design calculations. A parameter was investigated for correlating the blockage values against the combined effect of diffusion, curvature, and Coriolis acceleration. It was found that gross blockage accumulation correlates against this parameter with an uncertainty in blockage of ± six percentage points. Up to the point of the axial-radial bend of the flowpath, the analysis shows that blockage is controlled equally by diffusion, flowpath curvature, and the combined effect of blade curvature and Coriolis acceleration. In the radial portion of the impeller, further increase in blockage is controlled by Richardson number.

On the Relevance of Inviscid Subsonic Flow Calculations to Real Centrifugal Impellers Flow

The results of a fully three-dimensional inviscid compressible calculation technique for the flow field inside centrifugal impellers are compared to optical measurements in an open, radial exit impeller. It is concluded from this comparison that as long as viscous influence, including its displacement effects (manifested mainly in the jetwake flow structure), are not too big, the inviscid method applied can be used with confidence. When the viscous influence is such that it distorts the flow field in certain regions but displacement effects are still insignificant, the inviscid method can be used outside regions of viscous dominance. This situation occurs about halfway downstream, through the impeller. Only when displacement effects resulting from viscous flow field distortions, become big and the jet-wake profile becomes fully developed, does the inviscid method fail to predict the correct flow field. This happens at the exit of the impeller investigated here.

Slip Factor of a Centrifugal Compressor and Its Variation with Flow Rate

To predict the complete performance map of turbocharger centrifugal compressors, it has been found essential to include a procedure for estimating the slip factor at off-design flow rates. The many correlations available for the slip factor only concern themselves with design-point operation and consequently only provide a single value for the slip factor. The approach presented here attempts, within the confines of a one-dimensional procedure, to recognize the changing flow pattern at the impeller discharge in order to predict the variation of slip factor with flow rate. The procedure is based upon the well-established jet-wake flow model of Dean and the overall slip factor calculated from the jet slip factor. Experimental and theoretical slip factors are presented for three impellers with 34, 30 and 12 radial blades, respectively. The complete performance map of the 12-bladed turbocharger compressor and the effect of using a constant and varying slip factor on the predicted performance are presented.