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National Advisory Committee for Aeronautics, Report - Analysis of Spanwise Temperature Distribution in Three Types of Air Cooled Turbine Blade

Methods for computing spanurise blade—temperature distri-
butions are derived for air-cooled hollow blades, air—cooled
hollow blades with inserts, and air—cooled blades containing
internal cooling fins. Individual and combined ejects
on spanwise blade-temperature distributions of cooling-air—
temperature change due to heat transfer and rotation, radiation,
and radial heat conduction are determined. In general,
the efl'ects of radiation and radial heat conduct-ion were found
to be small and the omission of these rariations permitted the
construction of nondimensional charts for use in determining
spanwise temperature distributions through air-cooled turbine
blades.

An approximate method for deter-mining the allowable stress—
limited blade-temperature distribution is included, with brief
accounts of a method for determining the maximum allowable
efectice gas temperatures and the cooling-air requirements.
Numerical examples that illustrate the use of the various
temperature—distribution equations and of the nondimensional
charts are also included.

One of the most important, limitations imposed on the
design and the performance of aircraft gas-turbine power
plants is the strength of the turbine materials; this strength
decreases as the temperature increases. Turbine cooling
offers the possibility of removing this limitation, even with
the use of nonstrategic materials. Because of its relative
simplicity, the passing of air radially through the turbine
has been the subject of considerable investigation.

Theoretical and experimental studies made independently
in Germany, England, and the United States showed that
the circulation of cool air through hollow blades (fig. 1(a))
would allow the blades to operate several hundred degrees
below the efliective gas temperature. Experiments with
inserts showed further that. the required amount of cooling
air could be considerably reduced if an insert (fig. 1(b))
was used to block off the central, part of the hollow—blade
air passage.