The phenomena of unsteady relative flow observed in a centrifugal impeller passage running at part capacity and zero flow are discussed. The mechanisms of passage stall for a shrouded and unshrouded impeller are investigated and a qualitative correlation is developed for the influence of secondary flow and inducer flow on the passage stall. The hydrogen bubble flow visualization technique is extended to higher velocities and rotating systems and provides the method for obtaining the experimental results.
Airflows between centrally clamped, rotating, rigid disks are investigated with respect to the type of flow pattern, the parameters that influence nonuniform flow, and the effects of various flow patterns on disk stability. The experimental method uses a waterflow modeling technique for the airflow. The observed flow patterns are highly unsteady. The configuration and position of the shroud and slider arm are found to be the major parameters that influence flow characteristics. A reduction of disk flutter by a factor of 12 can be achieved when the unsteady flow pattern is changed to a steady flow pattern.
The complete velocity distribution, including both primary and secondary velocities, has been measured in passages of centrifugal impellers of simple shape. Comparison is made with theoretically predicted secondary vorticities based on a simple combination of an inviscid primary flow and a streamwise vorticity generation analysis. The measured velocities were obtained in a water-flow impeller rig using a miniature, cylindrical, hot-film probe positioned on the rotating impeller and traversed and controlled remotely through slip rings. The understanding of the complex flow patterns was assisted by a photographic study employing a hydrogen bubble, flow visualization technique.
Experimental measurements are presented of the velocity field near the exit of a radial impeller with backward-curved blades. The flow pattern, and its variation with changes in the flow coefficient, are compared with numerical predictions on a blade-to-blade plane. The theoretical flow prediction method assumes inviscid flow, is essentially two-dimensional and is based on the streamline curvature approach. It does not specifically require the condition of zero absolute vorticity. The comparison with experiment indicates that the principal feature of the flow not accounted for in the inviscid model is the region of low velocity near mid-blade height on the suction surface, especially for higher blade loadings.
Howard and Lenneman have done an excellent job of getting secondary flow measurements in centrifugal impellers. The results certainly show the importance of secondary flow and also that qualitative results may be obtained even with a one-dimensional calculation.It would be of great interest to see a comparison of the calculated primary flow with the measured velocities of Figs. 6 to 10. Also, a comparison of the calculated secondary flow with the experimental results would be informative.Very little comment was made in the paper on the flow visualization results.Based on primary potential flow on a two-dimensional blade to blade plane for the radial impeller, I would expect cross passage velocities from pressure to suction surface near the inlet and from suction to pressure near the outlet. This trend is observed in Figs. 7 to 10. Fig. 9 is noteworthy in that the cross flow varies so much near the shroud. Since this impeller is shrouded and the flow is reasonably symmetrical from hub to shroud at station
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.