Abstract
Certain applications for turbines require units with a large work output per stage. The whole of the expansion takes place across the nozzles and at inlet to the turbine blades the gas velocity is supersonic. Impulse blading is usually employed with flow turning angles ranging from 90° to 160°. However, advancing steam conditions suggest that the first stages of turbines presently designed with subsonic blading may have to accept increasing heat drops to reduce the steam temperature to the first moving row and to reduce gland losses. Under these conditions blading designed to accept supersonic velocities could be employed.
This paper, which deals with blading designed specifically for supersonic flow, is divided into two parts, the first of which outlines the theory and design of the blading. The second part describes tests run on cascades of these blades and discusses the results. In Part I a design method based on inviscid isentropic supersonic vortex flow theory is evolved in which the uniform flow ahead of the blade is transformed into a vortex flow, turned through the required angle and then converted back to uniform flow again at the exit. The blades thus obtained are cusped and a design method has been developed to produce blades with finite leading and trailing edges. Blades designed on this basis were tested in cascade and the results were used to modify the design procedure.
The revised design method for non-isentropic conditions incorporating the measured losses and allowable contraction ratio was programmed for a Ferranti Pegasus digital computer and this was used to produce an impulse blade section with a flow turning angle of approximately 137° and capable of accepting an upstream Mach number of 1.285 and a blade inlet Mach number of 1.514.
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