National Transonic Facility Characterization Status

34 Pages·2000·1.1 MB·English

by  Bobbitt, C., Jr.

AIAA-2000-0293
National Transonic Facility Characterization
Status
C. Bobbitt, Jr., J. Everhart, J. Foster, J. Hill, R. McHatton, and
W. Tomek
NASA Langley Research Center
Hampton, Virginia
38th Aerospace Sciences Meeting & Exhibit
10-13 January 2000
Reno, Nevada
For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics,
1801 Alexander Bell Drive, Suite 500, Reston, Va, 20191-4344
_j
AIAA-2000-0293
NATIONAL TRANSONIC FACILITY CHARACTERIZATION STATUS
C. Bobbitt, Jr., J. Everhart, J. Foster,, J. Hill, R. McHatton, W. Tomek
NASA Langley Research Center
Hampton, Virginia USA
A_str_t non-uniformities or unsteadiness, or adverse
model/tunnel wall interactions. The amount of
This paper describes the current status of the deviation allowable in the flow field from the
characterization of the National Transonic target flow is governed by the required
Facility. The background and strategy for the accuracy in the desired measurements.
tunnel characterization, as well as the current Therefore, to provide high-quality wind-tunnel
status of the four main areas of the data, we must determine the required
characterization (tunnel calibration, flow accuracy in measurements; translate these
quality characterization, data quality requirements into requirements on the flow
assurance, and support of the implementation field; determine if the tunnel flow meets these
of wall interference corrections) are presented. requirements; and determine the impact and
The target accuracy requirements for tunnel possible solutions if the flow field does not
characterization measurements are given, meet these requirements.
followed by a comparison of the measured
tunnel flow quality to these requirements Facility Background
based on current available information. The
The NTF was primarily designed to achieve
paper concludes with a summary of which flight-Reynolds numbers at transonic speeds
requirements are being met, what areas need
using a combination of high pressures and
improvement, and what additional information
cryogenic temperatures. It is a closed-circuit
is required in follow-on characterization
tunnel with a single-stage compressor, a 15:1
studies.
contraction ratio, and a 25-foot long, 8.2-foot
square test-section with filleted corners. The
National Transgni_ Facility (NTF) test-section can be run in a slotted-wall (top
Characterization Backqround and bottom walls slotted with a 6-percent
openness ratio) or a solid-wall configuration.
Characterization Backqr0und Figure 1 shows a layout of the tunnel, with the
nitrogen injection ring between turns 1 and 2,
The purpose of wind-tunnel testing is to study
the inlet guide vanes, fan, and stators between
aerodynamic phenomena in a known,
controlled environment that matches a desired turns 2 and 3, and the heat exchanger and
four turbulence reduction screens in the
target flow condition. Any deviation in the flow
settling chamber just upstream of the
field from this target flow results in
contraction region. Tunnel specifications are
inaccuracies in the desired measurements.
This deviation can be due to the freestream given in Table 1. The tunnel can be run with
either air or nitrogen as the test-medium. In
• Test-section area: 8.2 ft. x8.2 ft
* Mach range: 0.10 to 1.2
• Pressure range (atm.): 1to 9
• Temperature range (F): -260to 130
• Max Reynolds number 120 million / ft.
"Copyright© 1999bytheAmerican
(based on chord or 0. I*sqrt(test-section area))
Instituteof Aeronauticsand
Astronautics, Inc. NoCopyright is
asserted inthe UnitedStatesunderTitle Table 1- NTF Specifications
17,U.S.Code.The U.S.Government
has aroyalty-freelicense to exercise all
rights underthecopyright claimed
hereinforGovemmental Purposes.All 1
otherrightsarereservedbythe
American Institute of Aeronautics and Astronautics
copyrightowner."
the air mode, temperature control is achieved customers who frequently test at the NTF to
using a water-filled heat exchanger; in the determine what accuracy is being sought for
nitrogen mode, temperature control is these aerodynamic measurements. These
achieved by the injection of liquid nitrogen into requirements are shown in Table 2.
the flow. Mach number control is achieved Subsequently, all characterization efforts have
using acombination of selected fan speed and been focused on meeting these requirements.
inlet guide vane angles. The NTF can test
sting-mounted full-span models and sidewall- The NTF characterization effort consists of
mounted semi-span models. four main areas: tunnel calibration; flow quality
characterization; data quality assurance; and
NTF Characterization Strateav support of the implementation of wall
The first step in developing the strategy for the interference corrections. The calibration and
characterization of the NTF was to create an flow quality areas focus on the short-term
overarching process that would result in accuracy of individual flow parameters
verifiable flow quality and data quality that met throughout the test-section over the operating
customer expectations. The process created range of the tunnel. The data quality
for the NTF characterization is shown as a assurance thrust is designed to provide
flow chart in Figure 2. The first step in the accuracy of calibration parameters and force
process is to determine the customer accuracy coefficients both short-term and long-term,
and to insure that the tunnel measurements
requirements for aerodynamic measurements
made at the NTF. These requirements are remain stable. The support of the
then used to compute accuracy requirements implementation of wall interference corrections
for the flow parameters using the technique of provides information critical for correcting
propagation of errors. Next, the flow biases in the aerodynamic measurements due
parameters are measured in the wind-tunnel to modeVtunnel wall interactions.
and compared to the accuracy requirements, tf
the requirements are met, the flow parameters Two novel ideas were incorporated in the NTF
must be periodically checked to insure characterization strategy. The first was to
continued compliance. If the accuracy divide the test segments into short-duration,
requirements are not being met, corrective self-contained tests. This approach allows the
action must be taken, and measurements ability to fit characterization tests into small
made to see if the flow parameters then windows of opportunity, which results in
comply with the requirements. This process is minimum impact to the tunnel schedule.
to be continued throughout the life of the wind- Additionally, this strategy allows time for
tunnel, with periodic review to insure lessons learned in one characterization test
measurement accuracy requirements meet segment to be implemented in any following
current testing needs. test. The second idea was to publish and
present all characterization data as soon as
Accuracy requirements at the NTF are driven possible. This openness of communication
by performance testing, and are most stringent allows customers testing at the NTF to better
for measurement of lift and drag coefficients. understand their data, and encourages
Input was obtained from several industry customer feedback with input and insight into
• 0.4% CL,Coabsolute
• 0.2% CL,COincremental
Transonic cruise
• 1count Coabsolute
• 1/2 count COincremental
Table 2- Customer Accuracy Requirements
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possiblecausesandcorrectionsif the flow
quality does not meet the accuracy
Temperature Characterization
requirementisnacertainarea.
Temperature measurements have been made
at the NTF using a thermocouple grid located
The remainderof this paperprovidesthe
in the settling chamber between the cooling
status of the four areas of the NTF
coil and the most upstream anti-turbulence
characterization.
screen. A layout of these thermocouples is
found in Figure 3. These measurements
Calibration and Empty Tunnel FI0w Quality provide an expedient inexpensive first-look at
how well the NTF approaches the desired
temperature uniformity requirements.
Flow Quality Requirements
Much work has been done in previous efforts
The settling chamber temperature
to determine accuracy requirements for wind-
measurements were made over the operating
tunnel measurements and translate these into
range of the NTF up to a dynamic pressure of
requirements for the wind-tunnel flow. Most
3500 psf. Data presented in Figure 4 and
notably, a recent in-depth analysis of flow
Figure 6 show the offset of the reference
quality requirements was completed and
temperature measurement and the
documented by the National Wind Tunnel
temperature variation, respectively, over a
Complex (NWTC) Project team consisting of range of Mach and Reynolds numbers at three
members from the U.S. government, industry
tunnel temperatures. Each symbol
and academia. These NWTC Project
corresponds to an individual data point taken
requirements were determined to be the best
at one condition. The reference temperature
approximation of an agreed-upon national
offset was determined by subtracting the
standard for wind-tunnel flow quality, and were
reference temperature measurement (made
therefore adopted as goals for this flow quality
using a platinum resistance temperature
characterization effort. Table 3, taken from the
device located in the settling chamber
NWTC documentation (Binion/Steinle'),
downstream of the cooling coils and the four
provides a summary of the parameters
anti-turbulence screens) from the average
defining the flow field and accuracy
settling chamber temperature calculated from
requirements for both low-speed and transonic
all the measurements on the thermocouple
testing.
Parameter Low Speed Requirements Transonic Requirements
Total TemPerature
Reference 1deg F 1deg F
Distribution 1deg F 1deg F
Fluctuations
Turbulence 0.05% 0.05%
Noise 0.3% qinf 0.3% qinf
Stream Angle
2-sigma along span 0.1 deg 0.1 deg
Gradient 0.014 deg/ft 0.023 deg/ft
M.achNumber
Reference 0.0004 (M=0.3) 0.0005 (M=0.8)
Gradient 4xl 06/ft (M=0.3) 2xl 05/ft (M=0.8)
Total Pressure 3psf (M=.3, PT-- 5atm) 5.5 psf (M=.8, PT= 5.5 atm)
Static Pressure 3psf (M=.3, P_= 5atm) 5.5 psf (M=.8, PT= 5.5 atm)
Total Temperature 1deg. F 1deg. F
Table 3- Flow Quality Requirements
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grid. The temperature variation was on the order of 0.3% of the test-section
represented for the purposes of this paper as dynamic pressure, and are consistent from the
twice the standard deviation of the test-section through the high-speed diffuser.
temperature measurements made with the At the supersonic conditions, the pressure
thermocouple grid. In both figures, the fluctuation level jumps up to 0.5% at the arc-
dashed-line box highlights the requirements sector fixed fairing (at the downstream end of
for the accuracy and variation. the test-section) and in the high-speed
diffuser, but decreases to about 0.1% in the
Figure 4 shows that the reference test-section. This drop in test-section pressure
temperature accuracy appears to meet fluctuation levels can be explained by the
requirements at the warm temperature (120 presence of a shock at the downstream end of
F), but is outside the requirements at the the test-section at the supersonic conditions
cryogenic conditions (-150 F and -250 F). which prevents disturbances from propagating
Furthermore, the reference temperature upstream. This pressure fluctuation data,
accuracy seems to get worse at the higher obtained recently at the NTF, agrees with
Mach numbers, up to a maximum bias error of similar data taken previously in the NTF
8 F. Closer examination of the temperature (Igoe2).
variation across the settling chamber reveals a
possible source of this bias. Figure 5 shows Flow Anale Characterization
the constant temperature contours in the
Currently no information is available for the
settling chamber for a typical high Mach
local flow angle distribution across the test-
number cryogenic condition. Although some of
section inthe NTF. However, information does
the temperature contours are highly subjective
exist on the integrated flow angle, calculated
due to the thermocouple layout, itdoes appear
using upright and inverted runs of numerous
that the coldest gas temperatures are
models. Recently this information was plotted
concentrated at the bottom of the settling for similar models at similar test conditions to
chamber, which coincides with the reference
determine the stability of the flow angle over
temperature measurement location.
time. These data, shown in Figure 8, show
clear signs of achange occurring in the tunnel
The temperature variations shown in Figure 6
flow angle brought about by the removal of a
reveal that the temperature variation in the
splitter plate attached to the arc-sector fixed
settling chamber is greater than desired at all
fairing. This splitter plate, shown in Figure 9b,
conditions, and that the variation increases
extends the chord of the arc-sector/fixed
with increasing Mach number. The data in
fairing (Figure ga) and was added during a
Figure 6 combines repeatability, bias, and
recent tunnel shutdown. When this large
gradients into a single number for comparison
change in flow angle was noted, there was
to the requirements. This technique of
concern the calibration of the tunnel, done
reducing these separate types of variation into
without the splitter plate installed, may have
one number can limit the understanding of the
been affected. Therefore, the splitter plate was
data.
removed to return the tunnel to the
configuration at which it had been calibrated.
T_Jrbulence and NQi_e Characterization Subsequent tests showed that the integrated
Fluctuating pressure measurements in the flow angle returned to its historical value of
NTF have been made using wall-mounted approximately 0.14 degrees for a transport
fast-response pressure transducers at several model at transonic conditions. This instance
tunnel locations from the contraction region proved the worth of charting tunnel data over
through the high-speed diffuser. Figure 7 time.
shows the ratio of rms values of the fluctuating
pressure measurements (integrated from 1 Hz M_.ch Nvmber (_haracterizatiQn
up to 150 Hz) to the test-section dynamic The tunnel has been recently calibrated for
pressure as a function of tunnel location for both the slotted- and solid-wall configurations.
four combinations of dynamic pressure and The slotted-wall calibration covered the test-
Mach number (two transonic and two envelope up to a dynamic pressure of 3500
supersonic conditions). For the two transonic psf, while the solid-wall calibration was limited
Mach numbers, the pressure fluctuations are
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to a maximumMachnumberof 0.45.Both
The NW-I'C requirements on the longitudinal
calibrationswere made using a 3-inch Mach number gradients are based on the
diametercenterlinepipethathasfourrowsof desire for a buoyancy drag correction of one
staticpressureorificesspaced90 degrees drag count or less. Therefore, the buoyancy
apart.Asketchofthiscenterlinepipemounted drag correction for each calibration test
in thetunnel,alongwiththepressureorifice condition was calculated for a typical NTF
layout,isshowninFigure10.Datafromthe model, having a model volume of 0.884 ft3and
centerlinepipewereusedtocalculatea Mach a reference area of 2.6 ft2.The results for the
numbercorrection(adjustingthe reference slotted-wall calibration are shown in Figure
Machnumbertothecenterlinevalue)andto 13. This plot indicates that requirements for
determinethe Mach number longitudinal buoyancy drag are being met in the transonic
gradient(usedinthecalculationofbuoyancy region (for which the tunnel was designed),
dragcorrections). and are not met at the low-speed and
supersonic conditions. Again, further work will
Figure11showsanexampleofthecalibration be done to assess the effect of the orifice bias
data for a given test condition.At each errors on these calculations.
calibrationtestconditiont,hreeback-to-back
points were taken. The 95% confidence
Tunnel Stability Characterization
intervalsareprovidedforeachpressureorifice
Figures 14 and Figure 15 plot the stability
measuremenbt,asedon thevariationin the
overtime oftotal and static reference pressure
three back-to-backmeasurements.It is
measurements and the reference temperature
evidentfrom Figure 11 that the variation
measurement for a low-speed and transonic
betweenorificesis muchgreaterthan the
cryogenic condition. To measure the stability,
variationbetweendatapoints.Previoustests
the tunnel was held on a condition while data
ofthiscenterlinepipeweremadewherethe
pointswere taken over a period of time. The
pipe was movedlongitudinallyin the test-
time-span was 1.5 minutes for the low-speed
section.It was notedthat the patternof
conditionand2 minutes for the transonic case.
variationbetweenorificesmovedwith the
During this period, nine data points were
centerlinepipe location,indicatingthat this
obtained, and are those shown on the plot.
variationis causedby imperfectionsin the
The total pressure stability was within the
orificesT.heinitialcalculatioonfMachnumber
required limits for both the low-speed and
variationd,escribedbelow,dealsonlywiththe
transonic conditions. The static pressure
variationbetweenpoints.Furtherworkwillbe
stabilitymet the requirements at the low-speed
donelatertoincorporatetheorificebiaserror
condition, but exceeded the limits at the
intotheMachnumbevrariation.
transonic condition. Conversely, the
temperature stability was within limits
TheMachnumbervariationwascalculatedby
transonically, but slightly out of tolerance for
poolingthe variancefor all centerlinepipe
the low-speed case. To adequately
measurementsmadewithinthe modeltest
characterize the temperature stability for the
volume.Thetestvolumefortheslotted-wall
low-speed condition, though, a larger
configurationshownin Figure 10 extends timeframe of data is required, as the
from test-section station 10 (test-section temperature limits of the temperature
stations measured in feet from the start of the
fluctuation do not appear to have been
test-section) to station 16. The solid-wall test reached.
region extends from test-section station 9 to
station 17. The Mach number variation for the
Data Quality Assurance Proqram
slotted-wall test-section configuration is shown
in Figure 12. Again, the dashed-line box
Historically, facility personnel were trained to
highlights the accuracy requirements. As
detect and correct blunder-type errors and
seen, based on short-term repeatability the
abnormally large data scatter. In addition,
Mach number accuracy requirements are
single-point calibration methods were used for
being met for almost all conditions (the
making major corrections. Assessment of
exception being at some supersonic
repeatability was based on relatively short-
conditions).
term, small sample, methods which are
incapable of determining measurement
5
American Institute of Aeronautics and Astronautics
stabilityandyieldso fewdegreesoffreedom
S, ft2 1.988
thattheycannotreliablyassessmeasurement
_', in. 5.74
uncertainty nor point to potential
improvementsunlessthe effectsare much b, in. 52.97
largerthanthenormasl catterT.heinitialeffort N, Ib, 6500
in the new data qualityassurance(DQA) A, lb, 400
program,whichwascompletedinFY99,was
PM, in.-Ib, 13,000
to find an appropriate measurement
assurancemethodologyto,trainthestaffinits
Table 4- Model and Balance Specifications
use,andto beginimplementationT.heonly
credible approach with the necessary
traceabilityseemsto be the Measurement A minimum of four repeat-run sets is obtained
Assuranceconceptdevelopedforcalibration by the facility each year. A repeat-run set is
laboratoriesbyNISTandextendedforwind- called a "group" and consists of the following
tunneltestingby LangleyResearchCenter. runs back-to-back at the same test conditions:
Thekeyelementsofthisconcepatre
• Inverted polar
(a) Statisticaqlualitycontrolformeasurement • Upright pitch polar
(Shewhart3),
• Upright pitch polar
(b) Application of Shewhart's statistical
• Upright pitch polar
methodsto both short- and long-term
• Inverted polar
repeatabilit(yEisenhart'),
(c) Periodictestingofstableartifacts(check The first two runs and the last two runs form a
standards)and the use of Shewhart's
two-observation group that is used to estimate
controlchartsontheresultstodetermine
the short-term repeatability of the flow
themeasuremenstystemstability(Pontius
angularity. The middle three runs are used to
andCameronS),
form a three-observation group that is used to
(d) Repeat-datsaetsduringa customertest,
estimate the short-term repeatability of the
togetherwith appropriatescaling, for
pitch-plane uncorrected balance coefficients
comparison with the check standard
CN ,C_,, C,,,°. Long-term repeatability (and
results (Schumacher'),
(e) A standard method for referencing to a stability) is estimated from the variation of the
common state (free-air). The standard group averages over time. The short- and
used at the NTF is the wall-signature long-term repeatability groups are analyzed for
method. measurement stability and scatter level
(precision) using so-called Three-Way
statistical control charts.
Currently, the NTF is running check standards
periodically and assessing the short- and long-
Too few repeat-sets have been taken so far to
term repeatability for attached flow over the
model on statistical control charts. Repeat-run definitively state the behavior of instrument
sets are also obtained at the beginning and scatter (precision) as afunction of test section
end of each customer test for comparison with conditions so the estimated short- and long-
the suitably-scaled check standard results. In term standard deviations (_,,g, dbg)
addition, pre-test predictions and post-test
presented in Table 5 are pooled over the
statements of repeatability are provided to the
Mach and q range. The pooled degrees of
customer.
freedom for (_wg (short-term) and _bg (long-
Cheqk standard model tQ.stinq. term) are approximately 40 and 20
The check standard model for the NTF (shown respectively. The expected standard deviation
in Figure 16) is a subsonic transport model for a single data point for attached flow (for the
that is no longer used for any other kind of check standard) is the root-sum-square of
testing. The balance used l's the LaRC NTF
d,,g and Obg"
113C that is a one-piece moment-type. The
model geometrical characteristics and balance
_',,,, poin,= (:Y,,_+ (:Yhg
full-scale limits are given inTable 4.
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American Institute of Aeronautics and Astronautics
Check standard probe testing conducted in the NTF. In the future, it is
The repeatability assurance program expected that four such tests will be
described in the previous section for balance conducted each year. Although two tests is
coefficients is applied in a similar manner to considered insufficient to declare the
the repeatability of flow parameters, measurement system + test section to be in
specifically Mach number and dynamic statistical control, we will use the pooled
pressure, q. The method used is to obtain values obtained so far to estimate the
repeat data for a probe (shown installed in repeatability for Mach and dynamic pressure
Figure 17) in an empty test section (low- as shown in the Table 6. The pooled degrees
speed and transonic tunnels) or a wall of freedom for the within-group and between-
pressure upstream of the model area
group standard deviations, dws and Obg, are
(supersonic tunnels). A group consists of three
126 and 51 respectively. The standard
back-to-back repeat measurements at a single
deviation for a single data point is the root-
test condition. The following ratios are
computed: sum-square of dwg and dbg"
Cq "- qcenterline
qreference The estimated uncertainties of the tunnel
calibration data are believed to be about the
CM -- M centerline
same as the values given in Table 6. Check
M reference standard data have been obtained so far for
930 psf < q < 3000 psf . For conditions
where the centerline and reference values are
outside of this range, the scatter may be
computed using the total and static pressures
somewhat higher.
from the probe and the reference system
respectively. The repeatability of Cq and CM SuoDort of the Imolementation oLWall
expresses the variation associated with the Interference Corrections
test section itself and both sets of static and
total pressure propagated into the formulas for The NTF characterization effort also provides
computing Mach and q. information to support the development and
implementation of wall interference correction
Two check standard tests with a total of 63 codes for the NTF. This support includes wall
groups over 12 test conditions have been pressure data, wall boundary layer
Uncorrected coefficient d ,:g dbg donepoint
CA, 0.00002 0.00015 0.00015
CN" 0.00052 0.0022 0.0022
Cm" 0.00030 0.00056 0.00064
Table 5- Check Standard Model Short- and Long-term Variation
Within-group Between-group One-point
0.00036 0.0017 0.0017
dq/q
d MIM 0.00022 0.00092 0.00095
Table 6 - Check Standard Probe Short- and Long-term Variation
7
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informationa,ndcheckstandardmodeldata. a computational fluid dynamics (CFD) model
The followingsectionsprovidethestatusof of the NTF test-section.
this supporteffort,as well as presentinga
summaryofthestatusofthewallinterference Implementation of WItS in the NTF
correctioneffort.
The Wall Interference Correction System
(WlCS) code (Ulbrich 7)originally developed for
W_II Pr_sure_ the Ames 12-Foot Pressure Wind Tunnel has
tn the last couple of years, the wall pressure been implemented in the NTF for use during
measurement system at the NTF has been solid wall testing. WICS-generated wall-
improved to provide the high-quality wall interference corrections to an equivalent free-
pressure signatures necessary for the air flow field are computed using the wall-
implementation of wall interference correction pressure signature method combined with
codes. Empty tunnel wall pressure signatures balance measurements of model forces and
have been obtained for both the solid- and moments. Mean corrections for tunnel
slotted-wall test-section configurations. blockage and upwash are determined and are
then applied to the tunnel parameters. The
Wall Boundary Laver Heiaht code also provides the wall interference
Wall boundary layer measurements have been variation in the vicinity of model in the form of
made in the NTF for both the solid- and contour plots; this aerodynamic analysis-
slotted-wall test-section configurations. Figure enhancing capability is generally unavailable
18 shows a sketch of the boundary layer rake from simpler classical methods. The code has
design used for these measurements. For the been used in an off-line mode for semispan
slotted-wall configuration, two tests were run tests, and will be operational for fullspan
to provide boundary layer information at the testing in the first quarter of 2000. Because
seven different test-section locations shown in the method is fast and robust, it is well-suited
Figure 19. These locations were chosen to for real-time or near real-time application.
provide data on both the longitudinal boundary Efforts are currently underway to implement
layer growth in the test-section, and the WlCS for online post-point corrections.
boundary layer uniformity at a given test-
section station. Currently boundary layer data Sample interference predictions from a recent
for the solid-wall test-section configuration is large-model NTF test are presented in Figure
only available for the farside wall at station 22 and Figure 23. Here, uncorrected, the
12.77. A sample of the data is shown in classically corrected (AG-336, 1998), and the
Figure 20 and Figure 21. In both of these WICS-corrected solid wall measurements are
figures, the data presented as the average of compared with slotted-wall measurement
a combination of the measurements made obtained on the same model. Since the NTF
over a small region of the NTF low-speed was designed to minimize wall interference
envelope, with error-bars denoting the effects, the uncorrected slotted wall results,
variation at each location. The purpose for though not absolutely free of wall effects,
presenting the data inthis fashion is to provide should provide a good baseline from which to
a general magnitude of the boundary layer reference the correction. Effects included in
height, longitudinal growth rate, and the classical corrections are those due to
uniformity. Figure 20 reveals that the blockage (solid and attached wake), lift, and
boundary layer height averages between 3 streamline curvature, while WlCS includes
and 4 inches at test-section station 13 over these and additional effects due to any
this range of conditions. At these same separation of the model wake. Figure 22
conditions, it is seen in Figure 21 that the presents the lift correction, indicating an
boundary layer grows from about 1.2 inches in expected, large, lift-curve slope increase for
the contraction region up to 3-4 inches at the uncorrected solid wall data. Applying the
station 13 (the center-of-rotation for both sting- corrections rotates the curve into alignment
mounted and sidewall-mounted models). with the slotted-wall results. At low lift the two
correction methods are in close agreement,
This boundary layer height information has however, at the higher angles of attack the
been used in the development of semi-span difference between the methods widens to
model stand-off geometry and for calibration of about 0.005 in CL. Drag corrections are
8
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