Transonic and Low Supersonic Flow Losses of Two Steam Turbine Blades at Large Incidences

Abstract

A linear cascade experiment was conducted to investigate transonic and low supersonic flow losses of two nozzle blades for the steam turbines. In the experiment, flow incidences were changed from −34° to 35° and exit Mach numbers were varied from 0.60 to 1.15. Tests were conducted at Reynolds numbers between 7.4×105 and 1.6×106. Flow visualization techniques, such as shadowgraph, Schlieren, and surface color oil were used to document the flows. Measurements were made by using downstream traverses with Pitot probe, upstream total pressure probe, and sidewall static pressure taps. The losses were found to be rather constant at subsonic flows. At transonic and low supersonic flows, the losses increased steeply. The maximum relative increase of the losses was near 700% when the Mach numbers increased from 0.6 to 1.15. However, the maximum relative increase of the losses was only about 100% due to very large variation of incidences. It is important to note that the effect of Mach numbers on losses was much greater than that due to the very large incidences for the transonic and low supersonic flows. A frequently used loss correlation in the literature is found not suitable to predict the losses of the tested blades for the transonic and low supersonic flows. From the current experimental data and some data in the literature, a new correlation for the shock related losses is proposed for transonic and low supersonic flows of turbine cascades. Comparison is made among the existing correlation and the new correlation, as well as the data of the current two cascades and other three turbine cascades in the literature. Improved agreement with the experimental data of the five cascades is obtained by using the new correlation as compared with the prediction by using the frequently used loss correlation in the literature.