Permeability variation of a taper-rolled wire cloth Page: 3 of 26
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NACA RM E56LIO
Porous materials such as sintered metals or closely woven wire cloth
may be suitable for the aforementioned applications. Research is being
conducted on both materials to improve their physical. and cooling char-
acteristics. Only the wire cloth is considered herein.
In general, wire cloths of standard weaves are too permeable and
must be processed in some manner to decrease permeability. Some experi-
mental investigations have shown how rolling or combined brazing and
rolling of wire cloth decrease the permeability (refs. 1 and 2). These
references show that reducing the wire-cloth thickness by rolling changes
the airflow markedly through the cloth, and in some instances combined H
brazing and rolling have a still greater effect on airflow. For example,
at a given value of the pressure-drop parameter, a brazed sample that was
reduced 42 percent in thickness passed only about one-fifth as much air-
flow as was passed by the unbrazed sample. However, the airflow through
the sample that was reduced about 23 percent in thickness was nearly the
same whether brazed or unbrazed. It was found that a brazed-rolled wire
cloth in most cases was too brittle and stiff to readily form into shapes
such as might be required for a turbine blade . The experimental turbine
blade reported in reference 3 had a shell fabricated from a rolled un-
brazed sheet of wire cloth.
In the design of blades and possibly other apparatus, variations in
permeability in one or more directions may be required. For instance,
reference 4 shows that both spanwise and chordwise variations in permea-
bility are necessary for a turbine blade to maintain the cooling-air re-
quirements at a minimum. The effect of chordwise variation in permeabil-
ity can be partially accomplished by using a constant-permeability shell
in conjuction with orifices at the blade base (ref. 4). As a consequence,
only spanwise variations in permeability need to be achieved.
It would appear that taper-rolling of wire cloth would provide the
necessary permeability variation and that references 1 and 2 could be
used to determine the thickness to which the cloth should be rolled to
obtain this permeability variation. Such a procedure presumes that the
geometry or distortion of the wires of a cloth rolled with a taper is the
same as when rolled flat, so that for comparable thickness both cloths
would have the same permeability.
The purpose of the present report is to determine whether the data
for taper-rolled wire cloth are in agreement with those of a flat-rolled
cloth, what effect rolling a wire- cloth with the taper parallel and per-
pendicular to the many wires has on permeability, and whether variations
in permeability required for a turbine blade operating at gas and shell
temperatures of 25000 and 10000 F, respectively, can be obtained within
a sheet of material by taper-rolling. For the purpose of this report,
the spanwise permeability variation of this turbine blade was selected
as an example for duplication. A stainless-steel wire cloth with 20x200en
2
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Diaguila, Anthony J. & Liebert, Curt H. Permeability variation of a taper-rolled wire cloth, report, February 13, 1957; (https://digital.library.unt.edu/ark:/67531/metadc63268/m1/3/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.