Pressure drop tests were conducted on available samples of low and high density tile, densified low density tile, and strain isolation pads. The results are presented in terms of pressure drop, material thickness and volume flow rate. Although the test apparatus was only capable of a small part of the range of conditions to be encountered in a Shuttle Orbiter flight, the data serve to determine the type of flow characteristics to be expected for each material type tested; the measured quantities also should serve as input for initial venting and flow through analysis

Lawing, P. L.

Nystrom, D. M.

English

NASA Technical Reports Server

NASA Technical Memorandum 81891
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THERMALPROTECTIONSYSTEMCOMPONENTS:HIGH
DENSITYTILE,LOWDENSITYTILE,DENSIFIEDLOW
DENSITYTILE,ANDSTRAINISOLATIONPAD
PierceL. LawingandDonnaM. Nystr_
(B&SA-TM-81891) ORBITE}_ rlIER,_AL PRESsurE N83-]3_60
DROP CHABACTERISTIC5 FO_ SH'ITTLE OflBfTE_
TII_BMAL E_OTECT_ON S¥STEfl COP,?ONZNTS" HIG_ i
DENSITY TILE, LOW DENSITY TILE, DENS!I"IED Unclas
LOW DENSIT_ TILE, AND 5T[iAIN ISOLAT!O_ PAD G]/18 28995
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OCTOBER1980
NationalAeronauticsand w__, '"v_e4 _ ¢/1:.. -_'._ C_
SpaceAclmlnistralion : :,
Haml_on,Virginia23665 /)._o ./
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https://ntrs.nasa.gov/search.jsp?R=19800024952 2020-03-21T15:45:18+00:00Z
PRESSURE DROP CHARACTERISTICS FOR ShaLE ORBITER _iERM.%L PROTECTION 8¥ST_24
COM2ONENTS: HIGH DENSITY TILE, LOW DENSITY TILE,
DENSIFIED LOW DENSITY TILE. AND STRAIN ISOLATION PAD
Pierce L. Lawing and Donna M. Nystrom
NASA Langley Research Center
SU_L_RY
Sudden external pressure changes during the Space Shuttle Orbiter
ascent and descent will impose pressure loads on the tile system due to
air trapped within and beneath the tiles. An example of such a pressure
change is the movement of the normal shock during the transonic portion of
the flight. In order to quantify these pressure loads it is necessary
to perform a venting analysis to determine how quickly the internal pres-
sures will change. In turn, a venting analysis requires pressure drop
characteristics of the tile system components. Pressure drom tests have
been conducted on available samples of low and high density tile,
densified low density tile, and strain isolation pad. The results are
presented in terms of pressure drop, material thickness and volume flow
A_+h_uhr_t_...... _ the test apparatus was only capable of a small part of the
range of conditions to be encountered in flight, the data serve to determine
the type of £1ow characteristics to be expected for each materlal type
_ested.
i
_. INTRODUCTION i
• The determln_tion of the heating and forces on components of the Space
Shuttle Orbiter tncrma2 protection system requires a knowledge of the equilibrium
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and dynamic flow of air internal to the components. For instance, an equili-
brium flow of air will take place through the system in response to an external
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pressure gradient, such as might exist in the neighborhood of a leading edge.
The passage of a transonic shock ma_ occur rapidly and result in dynamic
changes as air rushes in or out of t_e porous interior of the insulating
tiles, their strain isolators, and the filler bars which fill gaps between
the tiles. Further information on the thermal protection system m_y be
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found in reference 1.
There are a large number of individual tiles which when coupled with
varying geometry, different gap spacing, filler bars, strain isolation pad
thicknesses and a wide range of flow conditions, leads to a complex array
of venting and flow-through conditions to consider. A computerized analysis
technique would be very desirable to calculate internal flows and associated
heating, pressure distributions and loads. Primary requirements in developing
such an analysis technique are materials data, pressure drop characteristics
in particular, and known solutions with which to test and develop the technique.
A literature search quJ ckly reveals that there is no trustworthy
analytical approach available for predicting pressure drop parameters for
these materials, and that known solutions vary by orders of magnitude.
Summations of the ]iterature may be found in references 2, 3 and 4.
Accordingly, within the constraints of time, equipment and available test ,_
samples, an experimental program was undertaken to determine pressure
drop characteristics of tile and strain isolation pad or SIP material. It _ _
is the purpose of this document to present these experimental results. _
Test Apparatus and Procedure
A commercial unit originally used to determine the porosity of
parachute cloth was used for the present tests. The unit is a Frazler
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Porosimeter manufactured by the Frazier Precision Instrument Company,
8913 G!envil]e Road, Silver Spring, MD, and its operation is depicted in
the sketch shown in figure 1. A small centrifugal compressor draws air
through the apparatus as shown. Volume flow rate is determined by means
of a set of orifices, orifice calibration sheets supplied by the manufacturer,
and a differential Merriam Red Oil manometer. The orifice calibration
sheets supplied were for a 6.985 cm (2.75 in. ) diameter circular opening
at the test sample mountir.: flange, and a square openlm_ 2.54 am (i.0 in.) on a
side. The orifice calibration data for ol:eopening could be directly
converted by the area ratio of the two openings, to agree with the orifice
calibration data for the other opening, thus indicating that the
calibration factors are not a strong function of the exact size and shape of
the opening. Nevertheless, where possible, 6..085 cm diameter cylindrical
samples were suppl_ed for test, as shown in figure ] Tnere was not sufficient
material available to prepare such a SIP sampic and Lhis material was
tested in a single sheet as shown in figure i. The flow exit is approxl-
2
mately 0.25h x 5.08 cm (0.i x 2.0 in.) for an opening area of 1.29 cm
(0.2 in.2).
Pressure drop across the s_nple is the difference between atmospheric
pressure and the lower pressure in the chamber between the mounting flange
and the calibrated orifice, as shown in figure I. This pressure difference
is also read by a Merriam Red Oil manometer referenced to atmospheric
pressure. .%
To obtain pressure drop as a function oi" thickness, a cylinder of
tile material was first tested for the f%_llthickness of the tile sample
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(with the exterior coating removed). Readings were taken over a range of
vol_:le flow rates and for several appropriately selected orifices. A d_sc
was then sliced from the top of the cylin er and the readings repeated. _
A primary difficulty in these tests was prevention of leaks past the
sample being tested. To minimize this problem the tile samples were first !
coated with ordinary desk top rubber cement and then fitted to a cardboard
collar. The sample and its collar were then coated several more times
with at least 2-hour drying intervals between coats. Before testing, the
collar was (,,mented to the brass mounting flange. The SIP sample was
prepared by attaching cardboard to the SIP with double backed tape and then
coating all of the exterior, except for the entrance a/,dexit, with several
coats of rubber cement. This package was then mounted in a collar in a _
mam_er similar to the tile samples (fig. i). The SIP sample had a flow
length or thickness of 9.52 cm (3.75 in.); no tests were made to determine
flow characteristics as a flhnction of thickness (flow length).
RESULTS AND DISCUSSION
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Pre_sure drop as a _hAnction o£ material t.hickness for the high density
tile for selected constant v:Llues of volt_ne £1ow rate is presented in figure 2.
This particular tile sample was the thickest available and data were taken
for six different values of thickness resulting in the largest amount of
data for any one sample. As may be seen from figure 2, pressure drop is a
' linear function of the thickness for a consttmt volume flow rate. Figure 3 ;
t %
i presents the data for this same sample as volume flow rate as a function _ '-
of thickness for consta/_t values o£ pressure drop. Figure h presents the
data in terms of pressure drop as a functlon of volume flow rate for constant ;
4
values of thickness. Figures 2, 3, and h have presented the data cast in I
different variables to illustrate the flow characteristics as a function of }
h _
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each o£ the three variables. Figure h also presents the data for the low
density tile at comparable values of _mterial thickness. In addition to
the obvious differences in flow resistances of the two tile types, this I
demonstrates that pressure drop is essentially linear with volume flow Ifigure
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rate, a characteristic of low Reynolds number flows. At high Reynolds number,
the pressure drop would be exq0ected to vary as the volume flow rate squared. !
Figure 5 repeats the data of figure h with the data from a sample of
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densified low density tile and the SIP s_iple show_l for comparison. These I
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materials also exhibit low Reynolds number behavior in that they have linear
pressure drop characteristics as a function of volume flow rate. However, the i
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den_ified tile pressure drop data, figure 6, no longer exhibits linear behavior i
with tile thickness due to the nonlinear increase in density as the bonding
surface (zero thickness) is approached. On figure 6, this behavior is
compared with both the low and high density tile data presented previously
to indicate that the low density densified tile has pressure drop values
roughly equivalent to tilehigh density tile in the 1 to 3 em thickness range.
At thicknesses greater than the penetration of the densifying solution, the
slope of the pressure drop curve cs_ be expected to approach that of the
untreated low density tile_ this slope is included on figure 6 for reference
purposes. Although the distribution of the densifying material is unknown,
a speculative dotted line is included based on the approximate visual
; thickness of the densified layer (= .25 cm) and the supposition that for a
fixed volume flow rate, the pressure drop must approach zero as the thickness '
. approaches zero. The shape of the dotted line is further supported by the
observations in appendix ii of reference 1 where it is reported that the
densi_ing material ferms a dense crust about 0.5 mm thick with most of
the material remaining within about h mm of the bonding surface. This
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information is based on photomicrographs of a sample of densified tile
different from the one tested in the present report, however the steep
initial slope of the dotted llne is consistant with the observed
distribution of reference i. Thus, with increasing thickness from the
bonding surface, the pressure drop curve is expected to behave as indicated
by the dotted line, pass through the available data points and proceed
along, or at least become parallel to, the low density tile slope line.
APPLICABILITY OF RESULTS
Obviously, the full range of variables discussed in the introduction
have not been addressed in these tests. The particular problem that
triggered the conduct of the present test was the loadlng due to the
transient passage of a transonic shock wave during ascent. Pres_nably,
room temperature is adequate for these tests. However, neither the pressure
level or the transient nature of a passing shock have been simulated. At
higher pressure drops, the associated higher volume flow rates, the low
internal Reynolds number flow, which allows a linear relation between
pressure drop and volume flow rate, may change. Thus extreme extrapolation
of the present results may result in some error. The errors are, however,
expected to be second order in nature. Also, the present tests were
static in nature and a rapidly changing pressure may not provoke mass flow
in the same manner as the steady pressures used in these tests. A fine/
caution in applying these data is the limited number of samples some off
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which were cut from rejected or nonspecification materials.
CONCLUSIONS
Vo1'me rate of flow and associated pressure drop, measurements have
been made on samples from the interior of tiles and samples of strain
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isolation pad. These materials are typical of those to be used in the
Shuttle Orbiter thermal protection system and the measured quantities
should serve for initial venting and flow through analysis.
Specific conslusions are as follows:
• i. Material from the interior of a tile exhibits a linear pressure
drop as a function of material thickness for a constant volume flow rate.
2. For a constant value of thickness, material from the tile interior
has an approximately linear pressure drop with volume flow rate, displaying
the characteristicexpected for very low Reynolds number flows.
3. The strain isolation pad material has flow characteristicsvery
similar to the material from the tile interior.
4. Pressure drop as a function of material thickness for densified
tile is nonlinear as the bonding surface is approached for a constant
volume flow rate.
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References
i. "Orbiter TPS Strength Intcgrity Assessment." Battelle Columbus Laboratories,
June 16, 1980. (Final Report)
2. Parker, Jerald D. ; Boggs, James H. ; and Blick, Edward F. : Introduction
to Fluid Mechanics and Heat Transfer. Addison-Wesley Publishing
Company, Inc., Reading, Massachusetts, 1970.
3. "American Institute of Physics Handbook." Office of Science Information
Services National Science Foundation. McGraw-Hill Book Company, Inc.
h. "Viscous Fluid Flow," by Frank M. White (Professor of Mechanical and
Ocean Engineering), University of Rhode Island, Kingston, Rhode
Island, 197_.
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Orbiter thermal pressure drop characteristics for shuttle orbiter thermal protection system components:  High density tile, low density tile, densified low density tile, and strain isolation pad

Orbiter thermal pressure drop characteristics for shuttle orbiter thermal protection system components: High density tile, low density tile, densified low density tile, and strain isolation pad

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