Cooling characteristics of a transpiration-cooled afterburner with a porous wall of brazed and rolled wire cloth Page: 4 of 70
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NACA E54E25
a-
the turbine flange and the beginning of the porous wall, including the
fuel-spray bars and flame holder, was identical with the high-performance
afterburner configuration of reference 6, which was evolved from con-
figuration C of reference 7.
Cooling air from an independent source was filtered through 100
square feet of 1-inch-thick Fiberglas filter media that retained particles
greater than 1 micron. The flow was measured by means of an A.S.M.E.
standard thin-plate orifice. The plenum chamber and the high-temperature
impermeable wall upstream of the porous-wall section were Inconel, and
Ci the cooling-air side of the mild steel shroud was painted with zinc
chromate primer in order to eliminate the possibility of clogging the
wire cloth with fine scale.
The engine fuel was clear unleaded gasoline of 62-octane rating,
and the afterburner fuel was MIL-F-5624A, grade JP-4.
a Wire-Cloth Porous Wall
The porous combustion-chamber wall was made from wire cloth that
was brazed and rolled, for permeability reasons, as described in reference
3. The particular cloth used was monel 21x70 twilled Dutch weave
(designated cloth B in ref. 3) sprayed with three coats of silver solder
per side and brazed and rolled to a 35-percent reduction in original
thickness. The average final thickness was 0.0274 inch, and the average
permeability coefficient K was about 1xl0-8 square inch. The tapered
combustion chamber was lined with a porous wall made from 20 pieces of
wire cloth formed into shallow channels. Each channel was 1/2 inch deep
by about 41 inches long and tapered in width from about 4 inches at the
upstream end to about 3.5 inches at the downstream end. The channels
were spot-welded to angles (fig. 3) that were fastened to the structural
shroud by blind rivets. The permeability of each channel differed
slightly from the average permeability for all the channels . It was
expected that the cooling-air static pressure would vary somewhat
circumferentially because of the tangential inlet to the plenum chamber.
Therefore, the channels were arranged in an order that would tend to
produce a circumferentially uniform distribution of cooling air.
The newly fabricated porous combustion-chamber wall is shown in
figure 4(a). The channels of wire cloth were permanently bulged toward
the center line of the combustion chamber after the initial operation of
the engine. Figure 4(b) shows the bulged channels at the end of the
cooling investigation with cooling passage heights of about 3/4 to 7/8
inch in midchannel. The method of suspending the wire cloth caused a
minimum of disturbance to the cooling-air film on the gas side of the
porous wall, and the bulging of the channels reduced tensile stresses
in the wire cloth caused by pressure forces. The impermeable wall
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Koffel, William K. Cooling characteristics of a transpiration-cooled afterburner with a porous wall of brazed and rolled wire cloth, report, August 19, 1954; (https://digital.library.unt.edu/ark:/67531/metadc62507/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.