naca-tn-4091
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National Advisory Committee for Aeronautics, Technical Notes - Experimental Investigation of Transpiration Cooling for a Turbulent Boundary Layer in Subsonic Flow Using Air as a Coolant
Experiments were performed to determine the effect of injecting
coolant air through a porous sintered bronze plate into a constant-area
tunnel through which hot air was flowing. The boundary layer was
turbulent over the porous plate for all test runs. Tests were made with
either a constant coolant injection rate or a constant wall temperature.
The Mach number was approximately 0.6 at the upstream edge of the porous
plate and increased in the downstream direction. The mainstream stagna-
tion temperature was approximately 2150 F, and the coolant temperature
was either in the range -l5° to 5° F or the range -70° to -55° F.
It was difficult to run at the desired injection flow conditions,
because the permeability of the sintered bronze plate varied erratically
with both time and position. Nevertheless, a definite correlation ex-
isted between the porous wall temperature and the injected coolant-flow
rate; wall temperature decreased as coolant-flow rate increased. This
correlation for a given station along the porous plate appeared independ—
ent of the type of test when based on local conditions. A comparison of
the results with a theory for transpiration into a turbulent boundary
layer with an isothermal wall showed only qualitative agreement. This
was not unexpected, since some of the important assumptions of the theory
could not be completely satisfied in the experimental setup.
The problem of cooling a surface in contact with hot gases has be-
come increasingly important. Seweral methods of cooling have been stud-
ied. In reference 1, an analytical comparison of convection cooling,
film cooling, and transpiration cooling showed transpiration cooling to
be the most efficient method of the three. In transpiration cooling, the
coolant is passed through the heated surface and injected directly into
the boundary layer. This requires that the heated surface be constructed
of a porous material.
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