AIAA-87-1510 A Prediction Method for Flow in the Shuttle Tile Strain Isolation Pad P.L. Lawing, NASA Langley Research Center, Hampton, VA

AlAA 22nd Thermophysics Conference June 8-1 0, 1987/Honolulu, Hawaii

For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 1633 Broadway, New York, NY 10019

A PREDICTION METHOD FOR FLOW I N THE SHUTTLE TILE STRAIN ISOLATION PAD

Pierce L. Lawing' NASA Langley Research Center

Hammon. Virainia

Abstract

The Shuttle Orbiter thermal protection system uses a Strain Isolation Pad (SIP) between the tile and the Orbiter. This pape r presents exper imenta l measurements of the pressure drop and associated flow rate through a sample of the SIP material. Included are data for a range of air densit ies representative of Shut t le ascent and re -en t ry t ra jec tor ies . Also presented a r e new theoretical and correlative methods which predict the experimental data. These methods will help in predicting venting characteristics of tile assemblies during ascent, and hot gas leak under the tiles during descent. The predictive philosophy developed is useful in the study of fibrous and porous media fluid mechanics.

Introduction

The rate of air flow through the Shuttle Orbiter Thermal Protection System (TPS) is a critical parameter in the TPS design. On ascent, the flow characteristics of the Strain Isolation Pad (SIP) determine the venting rate of the SIP. This venting rate partially determines the forces on the thermal tiles. Venting rate is especially important during the transonic portion of the ascent when the normal shock can rapidly pass over a tile. The large pressure drop across the shock imposes maximum dependence on the venting capabilities of the TPS. The pressure difference may tear the tile from the orbiter if the SIP can not vent quickly enough.

During descent, some parts of the Orbiter experience large local pressure gradients that are constant for significant periods of time. These local gradients produce flow through the SIP. The flow characteristic of the SIP is one element in determining how much hot air will circulate under the TPS. Filler bars of SIP-like material inserted between the tiles reduce the penetration of hot air. However. charring of the filler bars has occurred on several Shuttle flights. The char r ing is apparent ly directly related to the hot a i r circulation. References 1 and 2 discuss this problem in more detail.

To s tudy the damage potential of si tuations as described in references 1 and 2, one must calculate the flow through the TPS. This requires a knowledge of the resistance of the particular SIP material to the flow. The literature reveals engineering practice and data largely based on packed beds of sand and similar geometries (references 3, 4, and 5).

The TPS has several components. One component is the narrow empty channels (the tile gaps). Flow in the channels is amenable to study using lubrication theory. The other TPS components are all fibrous materials such as the filler bars, interior of the tile, and the SIP. Even for the relatively well known sand bed type of porous media, the literature usually recommends experimental determination of the resistance coefficient. Overall. the engineering practice involving flows in porous media is not well understood. In cr i t ical applications t h e designer must rely heavily on experimental data.

There has been a program at Langley to provide reliable experimental data on representative portions of the TPS. The data was used in a mathematical model to predict

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the internal flow for Orbiter TPS configurations. Reference 6 documents experimental results for the tile interior and a SIP sample. Reference 7 gives the results from a transonic wind tunnel simulation of internal flow in a portion of the TPS References 7, 8, and 9 present analysis of the wind tunnel experiment,

In the analysis of reference 7, it became obvious the SIP flow data in reference 6 was not adequate for all situations. There were no data on effects of changes in ambient pressure. Also there were no data on the effect of changes in SIP thickness due to vertical movement of the tile. Accordingly, an experimental program to provide additional data was initiated.

The new data include the effects of bath large changes in ambient pressure and limited vertical movement of the tile. For the tests of reference 6 the SIP material was 0.229 cm (0.090 in) thick For these tests the nominal thickness of the SIP material is 0.432 cm (0.170 in). Reference 10 presents the da ta f rom these tes ts with no theoretical comparisons. The present paper provides an analytical method for pressure drop predictions to compare with the data of reference 10. The analytical methods developed for this study will lessen the dependence of future investigations on experimental data.

Nomenclature

a A area b

2,

radius of SIP fibers (0.001 cm, 3 . 2 8 1 ~ 1 0 . ~ f t )

center-to-center spacing in idealized fiber matrix

drag coefficient drag coefficient dependent only on geometry skin friction coefficient drag for fibers normal to flow drag for fibers parallel to flow sum of normal and parallel fiber drag surface-to-surface spacing in idealized fiber matrix

SIP height with no compression or tension typical fiber length used for calculation

C permeability coefficient W

Cf D m D DFaSt:, d

h SIP height (thickness)

3 P pressure pambient pressure at SIP entrance Q volume flow rate

reference volume flow rate, h (w/Vo) = 4.483x10-' ms/sec = 0.01583 f?/sec dvnamic DreSSUre. I /?..fDv2) Reynolds'number'based on'fiber diameter Reynolds number based on fiber length velocity characteristic velocity = p/(2ap0) = 0.7428 m/sec = 2.437 ft/sec effective velocity in SIP interior width a t the face of the SIP sample pressure difference viscosity

SIP height parameter density standard value of atmospheric density density of material of an individual fiber bulk density of SIP fibrous material handbook density of nylon

1

Eaoerlrnent

AvDaratus and Procedure

Figure 1 shows a typical Shuttle Orbiter tile geometry detailing the SIP location. Figure 2 shows a sketch of the SIP Flow Simulator. Figure 3 is a photograph of the Flow Simulator.

- The simulator provides a flow environment similar to

that which exists in flight beneath a Shuttle Orbiter tile. The simulator allows accurate measurements of the flow rate and pressure drop characteristics of the SIP material. The inside of the SIP Flaw Simulator holds a sample of the SIP material. It also has entrance and exit sections leading to and from the SIP. These sections do not provide the same entrance and exit geometry as the actual tile-SIP configuration. However, once airflow reaches the SIP in the Simulator, the flow in the sample duplicates the flow in the actual SIP design.

Figure 4 is a schematic showing the location of experimental elements relative to the test flow. Pressure ports were installed to allow pressure measurement a t key locations. Ambient pressure was measured at the entrance section just ahead of the SIP. The SIP pressure drop was measured between a station just inside the entrance and one just before the exit of the SIP.

AS seen in figure 4, the flow passes into the entrance section on both sides. This gives an evenly distributed flow and reduces the pressure drop from the flow meter to the entrance section. An inlet flow control valve is used as well as an outlet control valve leading to a large vacuum sphere. This provides flow rate control and allows testing at sub- atmospheric pressures. Differential pressure measurements were made from port 2 to port 4 as shown in figure 2. This was across 13.018 cm (5.125 in) of the SIP material with the flow parallel to the bulk of the fibers.

w Elongated holes where the four main pieces of the SIP Flow Simulator bolt together allow variable height settings for the SIP material. By changing the height of the SIP, flow rate as a function of the available flow area is measured. The original SIP height under no load is 0.432 cm (0.170 in) for the sample tested. Other heights tested were 0.274 cm (0.108 in), 0.325cm (0.128 in), and 0.508 cm (0.200 in).

Data Presentation

Reference 10 presents the experimental SIP pressure drop data without analysis. Some of the key figures from reference 10 are repeated in this paper for comparison with the prediction methods. The SIP pressure drop data is presented as a function of the volume flow rate. Included are data for 9 values of ambient pressure and for 4 values of SIP height. The SIP was tested with flow parallel to the weave direction of the sample. This aligned the flow with the majority of the SIP fibers. Reference I I discusses flow i n f i b rous media both normal and parallel to f ibers . Reference 12 presents supporting data. Reference 13 also gives data for flow normal to fibers. According to reference I I , for a given pressure drop, the highest flow rate is for flow parallel to the fibers.

Backaround

The term porous is used to describe a wide range of materials. They include fired clay bricks, ceramics, powders, honeycombs, felts, foams, insulation, straw, and glass wool. Most of these materials fall into two groups: those composed of s ands or o t h e r quasi-spherical particles, a n d those composed of fibers. An array of tubes, such as found in honeycombs, is an example of a material that does not fit

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either group. It fits Somewhere in between. The less permeable structures are usually of the packed sand bed variety. The study of these porous materials accounts for the bulk of the literature beginning with Darcy in 1856.

The great interest in packed beds of sand relates to its importance to a wide range of practical problems. These include the flow of ground water, filtration rates, geology, petroleum technology, sewage systems, and nuclear or other waste disposal seepage rates. Reference 3 contains a discussion of methods for calculating flow characteristics for this class of materials. One of the advanced methods, based on an equivalent capillary tube bundle approach, is the Kozeny-Carmen equation. In packed sand beds, all of the particles are in contact with other particles. The particles therefore interact with the internal flow as a continuum rather than as individual particles. The flow resistance is a function of the shape of the path i t follows. This is a viscous dominated flow similar to pipe flow, which explains the success of the capillary tube methods.

However, the Kozeny-Carmen equation predicts levels of pressure drop greatly in excess of experiment for the loosely packed SIP fibers. The example in figure 5 shows that although this method works for sand beds, it does not work for fibrous SIP material. Lightly packed fibers have only occasional contact between fibers. Each fiber element is free to interact with the flow according to its particular geometry and orientation to the flow. Obviously, closely spaced fibers have increased interaction. There also may be a packing density high enough to make the fiber bundle have flaw characteristics similar to packed sand.

Present Amroach

Character izat ion of f ib rous mater ia ls is a lways difficult. The difficulty increases with smaller fibers and random orientations of the fibers. The fibers of the SIP material are very small. They form a flat fiber mat locked together by fibers of the material pulled through the mat using hooked needles. An acceptable model of the SIP material must be developed to proceed with the theoretical development.

Modeling of SIP fibers- The SIP material is a thin mat made of fibers primarily aligned either parallel or normal to the Orbiter structural shell. The parallel fibers make up the bulk of the mat and run essentially in the same direction. This produces a unidirectional weave pattern on the surface of the mat. The fibers normal to the shell were produced by the needling process. They are distributed across the mat in groups. This is not obvious to the naked eye. However, reference I5 contains SIP material characterizations which document the normal fiber groups.

Reference 15 also contains photomicrographs of the material which allow estimation of a typical fiber diameter. For the present analysis the diameter is estimated to be 20 microns (0.002 cm, 6.56 x 10.' ft). Due to the limited depth of field of photomicrographs, there is no corresponding method of estimating an average, or effective, fiber length. For the normal fibers, an appropriate length is the unloaded thickness of the SIP blanket, or 0.4319 cm (0.01417 ft). This length was assumed for the parallel fibers as well. This gives a fiber length to diameter ratio of 216. Based on these assumed dimensions the number density, the number of f ibe r s i n the sample, a n d the f i b e r spacing a re now calculated.

The number of fibers per unit volume is the mass of a unit volume divided by the mass of a single fiber. Reference 15 gives the density of the type of SIP used as 272 kg/m3 (17 Ib/fts). The fibers of SIP are nylon. The density of the fiber material is assumed to be the density of nylon, I134 kg/m3 (70.85 Ib/ft3). The number density is:

2

SIP mass/unit volume. I/fiber mass =

pSlp I / . . a * L ) (1)

= fiberslunit volume

For the present selection of parameters, this gives a number density of 177 billion fibers per ms (5 billion fibers per CIS).

In the experimental a r rangement , pressure ports measured the pressure drop across a fixed length of SIP material. The test volume of SIP is this length multiplied by the width and thickness of the sample. The number of fibers in the test volume is therefore:

(number density) *(SIP volume) = 1.389 x I O 7 fibers (2)

Fiber soacine, A means of visualizing fiber Spacing is helpful. Start by assuming all fibers to be parallel, equally spaced, right circular cylinders. Then assume each fiber centered in a long thin rectangular parallelepiped as sketched in figure 6. The volume of the parallelepiped assigned each fiber is the reciprocal of the number density. The area of the face of one of the parallelepipeds is the volume of a fiber divided by its length. If the fibers are assumed to be homogeneously spaced, the face of the parallelepiped must be square. Thus the length of one side, b, is the square root of the area. For the present example

b = [(l/number density). (l/L)]o.6

= 3.618.10~s cm (1.187.10.' ft) (3)

Note that b is also the centerline-to-centerline fiber spacing for the case of all fibers parallel. As the spacing decreases, the flow area does not approach zero. The flow area approaches the area of the square minus the cross-sectional area of the fiber. Note also that in this situation b = 2a and:

Amin/Am_ = (ba - =.a2) / b2

= (4a2 - n-a2)/4a2 = 0.2146 (4)

Parallel fiber draa coefficient. The parallel fiber drag coefficient was calculated using the theory of Glauert and Lighthill for long cylinders. (See reference 4 by White, Chapter 4, section 9.6.) This theory assumes *thick, laminar, axisymmetric boundary layer, and a pressure gradient of zero. The results are scaled by the long-cylinder parameter c, where f 2 = (x/a)' 1 Rex. AS f becomes larger, I > 100, C, approaches C,. The theory is approximate and the primary assumption of zero pressure gradient is being violated. Therefore, C, is approximated as C,.even when f < 100. Thus, in the present application, <' IS always used in the form

f 2 = (L/a)' / ReL ( 5 )

and is the primary length scaling parameter

Reference 4 considers a value of greater than 30 a long cylinder. This leads to an asymptotic-series expression for the skin friction coefficient (which is now assumed equal to the drag coefficient). An adaptation of this formula is used throughout this paper for the parallel fiber drag coefficient, The equation used is:

C, = ( (2/x + 0.577/xz - 0.835/xs)

where x = In (2.1). Terms in x of order higher than 3 are ignored. The curve labeled horizontol cylinder in figure 5 represents this relationship (assuming all f ibers t o be parallel.)

Normal f ibe r drag coe f f ic ien t . For the present investigation the Reynolds numbers are well below the turbulent, or critical value. There is no general theory for the drag of normal cylinders over this low Reynolds number range. Rather, there are a number of theories that fit parts of the Reynolds number range in a piecemeal fashion. However, reference 4 (chapter 3, section 10.2 and 10.3) gives a curve fit that bridges the theories as well as agrees with experimental data. AS used in the present work the f i t is expressed analytically as

C, = 1 + 10 (Re2s)-Z'S (7)

This function yields a value near 1, rather than the classic value of 1.2, for the drag coefficient at Reynolds number based on diameter, or Reza, on the order of IO5 . However, for the much lower Reynolds number of this investigation, typically 0.01 to 5 , i t provides satisfactory results. At these low Reynolds numbers, the flow is highly viscous in nature and drag coef f ic ien ts can be greater than 100. The meaningful reference length for the Reynolds number in this case is fiber diameter, or 2a, rather than the length as was appropriate for the horizontal case. If all fibers are assumed normal to the flow, this relationship gives the result labeled normal cylinder in figure 5 .

Total dran. In an earlier section a procedure was discussed for calculating the number of fibers in the SIP test sample. This number is used with an assumed ratio of parallel to normal fibers to provide the total number of parallel fibers. The total parallel fiber drag is calculated from the number of parallel fibers and the parallel fiber drag coefficient. This process is expressed by

Dpar = C, (2n a L) (9) (number of parallel fibers) (8)

and in a similar fashion,

Dnor = C, (2aL) (4) (number of normal fibers) (9) W

The total drag is then:

Dtdd = Dpsr + Dmr

Ap = D,o,&IP flow area)

(10)

and the associated pressure drop is defined as:

( 1 1 )

The pressure drop is plotted as the ratio Ap/pambient where pambient is the ambient pressure at the entrance to the SIP sample.

Assuming 10 percent of the fibers to be normal to the flow, and the rest parallel, the above method gives good results. Figure 5 shows this good agreement in a comparison with the experimental data at one atmosphere. This method gives a greatly improved prediction when compared to the Kozeny-Carmen method. Although not shown here, the agreement with da ta taken a t fractional parts of an atmosphere deteriorates rapidly with decreasing pressure and density. For these data the area correction discussed below in equation 13 is included. However, this does not account for viscous blockage, The flow area must be modified as described in the following section f o r a satisfactory prediction.

Effective flow area. The volume rate of flow, the velocity and the area are linked by:

V = QIA (12)

The square of the velocity calculated from equation 12 is used to calculate drag and finally pressure drop. Thus the area term strongly effects the relationship between flow rate and pressure drop. The simplest area term is the face area of

i.'

3

the SIP. This area is used to relate velocity in the duct ahead of the SIP to the measured flow rate. Once inside the SIP, the velocity must rise just due to the geometrical blockage of the SIP, expressed by,

which for the unloaded case = 1 - 0.24 = 0.16, v

This correction is global in that it recognizes the presence of the SIP material in the duct. However, it does not take into account the fiber geometry or orientation. For horizontal isolated fibers with no externally imposed pressure gradient, the fiber boundary layers encompass other fibers at the packing densit ies considered here. Under these conditions the problem of de te rmining interactions is extremely complex, even in an idealized matrix as sketched in figure 6.

However, confined flows, such as pipe flow, have limited boundary layer growth. Boundary layers become very thin in the presence of accelerating pressure gradients (see, for example, the discussion of Falkner-Skan flows in reference 4). Thus, the fibers may be isolated in the viscous sense, and the dominant effect of fiber spacing or density changes appears only in the changes in the flow external to the individual fiber. That is, increased blockage will decrease the area and increase the velocity of the external flow. This view of fibrous media flow phenomena is further strengthened by large scale flow visualization work reported in reference 14, which indicates a core of inertial flow between fibers.

Following the above discussion, a correction for the effect of changing the ambient density on the pressure drop is required. Accordingly, a functidn was sought that expressed a decrease in area (increased blockage) with density as the independent variable. Several functions were tried with the following formulation, where the increased blockage is represented by an effective area, proving the most successful when compared with the experimental data:

Aeff / ASlp = ( P/P , )'"' (14)

An effective velocity may now be calculated from

and this new velocity used to calculate a n effective Reynolds number, dynamic pressure, and the resulting pressure drop.

characteristic velocity, To conveniently manipulate equations and plot results, it is helpful to express variables in dimensionless groups. At this point a parameter is needed that can be used to normalize velocity. It is common in viscous flow problems IO define a characteristic velocity of the type p/(p.T) where T is a characteristic dimension. The principal independent dimension in this problem is the fiber diameter. leading to the relation

This characteristic velocity can now also be used to form a reference volume flow rate,

Qo = Vo * A. (17)

where A. = h, w

E f f e c t of SIP height. Extension of the theory presented above is necessary to account for the effect of changes in SIP height. Compression will reduce the height. Compression also is expected to reduce the flow rate (for a constant pressure drop.) Likewise, increases in height will increase the flow rate. This is partially accounted for by the

change in flow area due to the change in SIP height. However, for a satisfactory comparison with experiment a change must also be made in the effective area. This is accomplished by modifying equation 14 as;

Aeii / ASlp = ( P/P, )'"' (I/O('-') (18)

where = hSip/ho (19)

This function has a value of one for the undisturbed SIP height.

Comoarison of Theory With Exoeriment

Figure 7 presents experimental data for the SIP in the unloaded condi t ion , neither s t re tched nor compressed. F igure 7 also shows cons tan t density (pressure) curves generated by the theory jus t descr ibed . Dur ing the experiment it was impractical to hold precisely constant values of ambient density. Thus the success of the theory is somewhat be t te r than indicated by this comparison. However, the theory predicts the data very well over a wide range of variables.

The fraction of parallel and normal fibers in the theory was varied to obtain the best agreement with the one atmosphere data. The best agreement is with 90 percent parallel and 10 percent normal fibers. The exponent for the p I p term in equation 16 was varied for the best agreement wit[ other pressure (density) levels. Although two constants were tailored to get agreement with the data, the excellent agreement is remarkable for such a simple model. The agreement lends credence to the physics proposed for the flow in this type of media.

F igure 8 shows the comparison of theory with experiment for various SIP heights. The present theory is an obvious improvement in predicting the data.

A Global Correlation Method

The predic t ion method presented in the previous sections provides the necessary information about f low characteristics and material performance. However, it is desirable to have a less complex, more global, method for engineering use. A parameter frequently used to describe porous material in bulk is its permeability or its reciprocal, the resistivity. For example, the one atmosphere curve of figure 7 can be written as

AP / pambiant = ( ] I C ) * (Q/Qo)" (20)

where c is the coefficient of permeability. Although this is the commonly used definition (references 3, 4, 5 , 11, and 13). it has a serious shortcoming. Each new value of pressure (or dens i ty) requi res its own par t icu lar curve f i t and corresponding exponent and permeability value.

This shortcoming is also common to other porous material methods, whether experimental or theoretical. Reference 16 gives a method for finding a single loss coefficient for high Reynolds number viscous flows to represent the geometry independently of the viscous effects. The equations analogous to those used in reference 16 that apply to the present investigation are:

C = C D ' Re-'/" (21)

Applying these concepts to the present data gives the collapsed data set shown in figure 9 when the velocity term is replaced as defined in equation IS. The shown Curve fitted

to the data is a straight line and C,' is the slope of the line. In this example C,' has a value of 1.99 and I/n has the value of 0.8. Thus, an equation may be written

The very low Reynolds number data are better fitted by adding a second order term to the Reynolds number function.

Note tha t C; i s a dimensionless coeff ic ient o f resistivity. It is independent of pressure or density changes when defined in this manner. AS such, C,' is a function of only the geometry of the porous sample

An extension of the correlation can accommodate the effect of SIP height. In this instance the < function, equation 19, is not used to modify the effective velocity. Rather, it is used externally in the correlation to Simplify engineering application.

Figure 10 presents a data set as cast by this correlation. The data set was chosen to include the extremes of the pressures and heights tested. For clarity many of the data points shown in figure 10 have been excluded.

T h i s n e w m e t h o d o f r e p r e s e n t i n g t h e f l o w characteristics has two important advantages. It requires only one curve, or equation, to represent a large range of variables. Once you establish the relationship, this method needs only a few data points to determine the curve for a new geometry.

T h e da ta collapse of f igu re 10 demonstrates the excellent service performed by the functions in equation 26. It simultaneously correlates the variables of ambient density, flaw rate, and SIP height. It provides a global method of calculat ing pressure d r o p without having to sum the individual fiber drag values.

Conrlusians

The Shuttle Orbiter thermal protection system uses a Strain Isolation Pad (SIP) between the tile and the Orbiter. To evaluate the SIP performance requires a knowledge of the pressure drop of the fibrous SIP material.

The pressure drop through a sample of SIP material at conditions covering most of its operating envelope was measured. The experiment simulated the air flow beneath a tile exposed to a strong surface pressure gradient. The pressure across the SIP was varied from near 0 to 1.38.104 Pascals (2 psid). Testing was at constant levels of ambient density from atmospheric to 13.6 percent of the atmospheric value.

Conventional theories for prediction of pressure drop in porous media are unsuccessful when applied to the fibrous SIP material. A theory was developed to predict the pressure drop based on the drag of the individual fibers. A simple correlation method for the data was also developed.

These methods will he lp in predict ing the f low characteristics for the many SIP flow geometries of the Shuttle Orbiter tile system. They should also find wide application in the general study of the fluid mechanics of fibrous and porous materials.

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Referencet

Smith, D. S.; Petley, D. H.; Edwards, C. L. W.; ana Patten, A. B.: An Investigation of Gap Heating Due to Stepped Tiles in Zero Pressure Gradient Regions of the Shut t le Orb i t e r Thermal Protection System. Presented a t the AIAA 21st Aerospace Sciences Meeting and Technical Display, AIAA Paper No. 83- 0120, January 10-13, 1983.

Cooper, Paul A,; and Sawyer, James Wayne: Life Considerations of the Shuttle Orbiter Densified Tile Thermal Protection System. Presented at the Shuttle Performance: Lessons Learned Conference, Langley Research Center, March 8-10, 1893.

Massey, B. S.: Mechanics of Fluids, 2nd Edition van Nostrand Reinhold Company. New York, 1970.

White, Frank M.: Viscous Fluid Flow. McGrnw llill Book Company. New York, 1974.

Green, Leon Jr.; and Duwez, Po l Fluid Flaw Through Porous Metals. Journal of Fluid Mechanics, March, 1951, pp. 39-45.

Lawing, Pierce L.; and Nystrom, Donna M.: Pressure Drop Characteristics for Shuttle Orbiter Thermal Protection System Components: High Density Tile, Low Density Tile, Densified Low Density Tile, and Strain Isolation Pad. NASA T M 81891, October 1980.

Babbitt, Percy 1.; Edwards, Clyde L. W.; and Barnwell, Richard W.: The Simulation of Time Varying Ascent Loads on Arrays of Shuttle Tiles in a Large Transonic Wind Tunnel. NASA T M 84529, November 1982.

Dwoyer, Douglas L.; Newman, Perry A,; Thames, Frank C.; and Melson, N. Duane: A Tile-Gap Flow Model for Use In Aerodynamic Loads Assessment of Space Shut t le Thermal Protection System: Parallel Gap Forces. NASA T M 83151, July 1981.

Dwoyer, Douglas L.; Newman. Perry A,; Thames. Frank C.; and Melson, N. Duane: Flow Through Tile Gaps in the Space Shuttle Thermal Protection System. Presented at the AIAA 20th Aerospace Sciences Meet ing. AIAA Paper No, 82-0001, Orlando, Florida, January 11-14, 1982. W'

Springfield, R. Dean; and Lawing, Pierce L.: Flow Rate/Pressure Drop Data Gathered From Testing a Sample of the Space Shuttle Strain Isolation Pad (SIP): Effects of Ambient Pressure Combined With Tension and Compression Conditions. NASA T M 84591, May 1983.

Iberall, Arthur S.: Permeability of Glass Wool and Other Highly Parous Media. Journal of Research of the National Bureau of Standards, Vol. 45, NO. 5, November 1950. Research Paper 2150.

National Bureau of Standards Report to the Bureau of Aeronautics, Navy Department, Washington, D. C. L inea r Pressure Drop Flowmeters f o r Oxygen Regulator Test Stands. Reference 6.21621 1.2885. September 25, 1947.

Haugen, R. L.; and Wennerstrom, A. V.: On Predicting Flow Through Porous Media. Journal of Applied Mechanics. December 1970.

Dybbs, A.;and Edwards, R. V.: An Index Matched Flaw System For Measurements of Flow in Complex Geometries. Proceedings of Second International Symposium on Applications of Laser Anemometry to Fluid Mechanics, 1984.

Rasone, Philip 0.. Rummler, Donald R.: Microstructural Characterization of the HRSI Thermal Protection System for Space Shuttle. NASA T M 81821, May 1980.

Lawing, Pierce. L.; Adcock, Jerry B.; and Ladson, Charles L.: A Fan Pressure Ratio Correlation in Terms of Mach Number and Reynolds Number for the Langley 0.3-Meter Transonic Cryogenic Tunnel. NASA Technical Paper 1752, 1980.

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F i l l e r iAlumlnum F l l l e r b o i bor sk in

Figure 1.- Section view of typical Shuttle thermal protection Sysrern geometry showing relative location of strain isolation pad (SIP).

Pressure tops

E X l t sectlon cntronce sect ion -,

SIP locotion

Figure 2.- Section view of the SIP flow simulator for measuring flow properties of a SIP sample.

Figure 3.- Photograph of the SIP flow simulator with side plate removed.

Amolentroom oir

meter

Control valve

pressure

Pressure

Control volve

S I P f l o w SlmlJ lOfOr

Figure 4.- Schematic of piping and controls for SIP flow simulator.

9 horlrontol .2 c / / f ' + , 1 normal cylinders

.1 I//& Horizontal cy1 inders I I

2 3 4 0

Normollzed volume f l ow . Q/Qo

Comparison of data at one atmosphere ambient conditions with prediction methods.

Figure 5.-

Figure 6.- Idealized arrangement of horizontal fibers for use in theoretical model.

1.00 otm o 0.82 otm 0 0.68 otm 0 0.54 otm a 0.41 o t m n

~ ~ r r n ~ l i z e d oressuie 0 .27 otm 0 drop. PIP^^^^^^^

0

Tneory -

rlormollzed volume flow. Q/QO

Figure 7.- SIP pressure drop as a function of volume flow for a range of ambient pressures. Theory lines generated by assuming SIP fibers to be 90% horizontal and 10% normal cylinders.

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