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National Advisory Committee for Aeronautics, Research Memorandum - Analytical Investigation of Distribution of Centrifugal Stresses and Their Relation to Operating Temperatures in Gas Turbine Blades

An analytical investigation was made to determine the centrifugal-
stress distributions in six turbine-blade designs representative of
current turbine blades. The investigation also included. some con—
sideration of temperature effects in relation to centrifugal stress.

Sufficient experimental data were available on one type of tur-
bine blade to permit investigation of the effect of service operating
temperatures on the ability of the turbine blade to withstand loo-hour
operation at several different speeds. The stress analysis for this
blade indicated that failure would occur at a location approximately
halfway between the base and the tip of the blade. The number of
service failures that have occurred in this region corroborates the
analytical indication of critically low material strength.

A program is in progress at the NADA Cleveland laboratory to
investigate the problems associated with the stresses and the thermal
conditions that occur in various types of gas-turbine blade employed
in turboJet engines and turbine-propeller units. As a part of this
general program, calculations were made to determine the stress dis-
tributions that exist in six current turbine blades when these blades
are subjected to the centrifugal forces present during full-speed
service operation.

Superior design could be achieved if additional information
were available on the stress conditions that exist in operating tur-
bine blades. Analyses that provide a basis for comparing the
centrifugal-stress distributions inherent in Jet-engine turbine
blades of several designs currently in use were therefore made and
are presented. Comparison was made by considering the stress dis-
tributions in the individual blades in terms of percentage of blade
length. The turbine blades that were selected for this survey dif-
fered considerably in physical dimensions, but the design charac-
teristics were basically similar except for the integrally shrouded
blade.