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National Advisory Committee for Aeronautics, Technical Notes - Comparison Between Predicted and Observed Performance of Gas Turbine Stator Blade Designed for Free Vortex Flow

A comparison was made between the calculated design performnce‘
of a gas-turbine stator blade and its performance in a sector of an
annular cascade tunnel. Information was obtained with regard to the
three-dimensional effects that occur; the influence these effects have
upon various performance parameters are presented.

The gas velocities on the blade surfaces were computed by the
stream-filament method and compared with the experimental values.
The calculated values satisfactorily agree with the experimental
values.

The design conditions of free-vortex flow were not obtained.
The experimental tangential velocities were greater than the design
values at the tip of the blade but lower than the design values at the
root of the blade.

In the design of gas-turbine stator blades, compromises are
generally made between aerodynamic considerations and such practical
considerations as service life and cost of mnufacture. In order for
a turbine to perform efficiently and to meet design conditions of
power and weight flow of gas, however, the blades must be designed by
a procedure that accurately predicts blade performance.

The blade profiles are generally designed according to two-
dimensional-flow theory. The velocity distribution along the blade
surface must be such that flow separation or excessively high local
velocities will be avoided. This velocity distribution may be
determined by an incompressible potential-flow theory, which is appli-
cable for any solidity or camber of the blades (references 1 to 4).

These methods, however, do not consider commssibflity and are
mathemtically complex. Stream-filament theories that consider
compressibility may be used to design blades of high solidity.
These methods involve graphical integration of the flow equations.

Satisfactory experimental verification of either
the potential-flow theories or of stream-filament theories have-
previously been lacking.

The design performance of turbine stator blades based on free-
vortex flow as measured in a sector of an annular cascade tunnel
was determined at the NASA Lewis laboratory.