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National Advisory Committee for Aeronautics, Technical Notes - Torque-Speed Characteristics for High-Specific-Work Turbines

This report presents an investigation of turbine torque~speed char—
acteristics in a general form using the‘ideal specific work output cor-
responding to the turbine static— to total-pressure ratio as the normal-
izing 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 re—
sults 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 turbodrive 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 start-
ing torque over that at design speed.

In many turbopump applications there exists a need for knowledge
of turbine torque-speed characteristics. This need arises in order to
estimate (1) the starting characteristics of the turbopump and (2) the
stress of such.parts as shafting, gearing, and blading. Unfortunately,
very little reference torque-speed data are available for such purposes.
Furthermore, little information is available concerning the fundamental
studies of these characteristics.

As a consequence, an investigation of turbine torque-speed charac-
teristics in general form was made at the Lewis laboratory, with the re—
sults presented herein. The report first discusses the basis for the
selection of the form used in generalizing the correlation. This is
followed by an analytical treatment of the problem for single-, two—, and
three-stage turbines using the material in reference 1 in the high-
specific-work turbine operating range as a basis. Comparison of_the
analytical results is then made with available experrmental results.