Warner L. Stewart
This report presents an investigation of turbine torque-speed characteristics in a general form using the ideal specific work output corresponding to the turbine static- to total-pressure ratio as the normalizing parameter. These characteristics are first obtained using reference single-, two-, and three-stage analytical efficiency curves in the high-specific-work turbine operating range. Comparison of the results with available experimental data is then made to verify the trends of the curves presented. These analytical curves are used to provide a basis for estimating starting torque margin as a function of design-point requirements. An example turodrive application is also described to illustrate the manner in which the torque-speed curves can be used to establish the effects of staging on these characteristics. These studies showed that adding stages and reducing the criticalness of design with respect to the relation of specific work output to blade speed result in improved margin of starting torque over that at design speed.
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