Journal of Wind Engineering and Industrial Aerodynamics, 22 (1986) 129--148 129 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EXPERIMENTAL EVALUATION OF TEST SECTION BOUNDARY INTERFERENCE EFFECTS IN ROAD VEHICLE TESTS IN WIND TUNNELS
J.T. TEMPLIN and S. RAIMONDO
DSMA International Inc., Toronto, Ontario (Canada)
Summary
Vehicle aerodynamicists are aware that the boundaries of a test section can strongly influence the measurements of aerodynamic characteristics of vehicles tested in a wind tunnel. Wall interference was experimentally investigated in one solid and two open-area- ratio (OAR) slotted wall test sections. The blockage interference was studied using surface pressures from three scales of the Motor Industry Research Association (MIRA) notch-back reference model, representing 8.3, 13.0 and 18.7% area blockage. Tests were also performed using flat plates with area blockages between 1.6 and 20%.
A wall pressure signature matching method was used to determine the wall-induced "interference veloci ty" at the model location for the solid wall test section. Comparison was made between the predicted "free-air" pressures and those measured in the 30% OAR slotted wall test section. It was shown that a slotted wall test section can provide a virtually interference-free testing environment.
1. Introduction
Wind tunnels have been used for many years by designers of road vehicles including cars and trucks. The influence of the test section boundaries, which can be solid, partially open or completely open, on the measured aerodynamic loads and surface pressures of vehicles is one of the most commonly discussed problems. Blockage correction procedures, discussed in refs. 1--5, and their use in vehicle testing, discussed in ref. 6, have not proved to be universally applicable. The uncertainty in the magnitude of the block- age correction that must be applied has resulted in the car manufacturers testing in large facilities in order to test at low area blockages and thus reduce the uncertainty in their data. In recent years slotted wall and adaptive wall test sections have been proposed which require little or no blockage correction even at relatively high area blockages. It is important to recognize that differences in measured results from different facilities can be at tr ibuted to flow quality, model differences or testing procedures and not just bound. ary interference. The various factors and precautions that must be taken in order to obtain high quality data are discussed in ref. 7.
This paper describes a program undertaken to evaluate wall interference in solid and slotted wall test sections. The interest in the solid wall correction techniques was sparked by the need to obtain interference-free reference data to evaluate any residual blockage which may exist in a non-optimally designed slotted wall test section.
2. Test program description
The present study is an extension of research into the behavior of slotted wall facilities that began at DSMA six years ago [8, 9, 10]. The DSMA wind tunnel, suitable for 0.2 scale vehicle testing, was used for the present test program. The test section is shown in Fig. 1 and represents a full scale area of 22.32 m 2 . The walls and ceiling were modified to represent 0% (solid), 12 and 30% OAR. In each case the flaps at the downstream end of the test section were set to the position where further opening had no effect on the wall pressures at 95% of the test section length. Once the position was set for a given model, it was not adjusted for different yaw angles.
The MIRA reference test car with the notch-back configuration was chosen as the test vehicle because of its simplicity of shape and close re- semblance to actual cars. Three models were built at 0.2, 0.25 and 0.3 scale. The models were primarily of mahogany construction except for aluminum inserts that contained holes for surface pressure measurements. Basic dimen- sions of the vehicle are shown in Fig. 2 and the models are shown in Fig. 3.
_•'j• 4Dlffuser
" ] • ' • Wa~l (Wake) I / Static Tap
Adjustable / R$-Entry - ~ Flap, ~ / - - --
10LT~ 0.~5 L;S
i -
Plenum
0,41LTS ~i
Contraction <\
/ f
Ceiling (Wake) Stttlc Tap
Plenum Slat Slot
I I I I
Fig. 1. Wind tunnel test section con~iguration.
131
The models produced area blockages of 8.3, 13.0 and 18.7% in the DSMA wind tunnel.
Surface pressures were measured at 76 locations by means of a Scanivalve and pressure transducer system installed inside each model. Reference pressure lines and electrical cables entered each vehicle through a hole behind one of the rear wheels. A PDP 11/34 computer controlled the Scani- valve, acquired the pressure data and stored it for later analysis. Pressures were also measured on the ceiling and one of the side walls of the test section.
Flat rectangular plates (width to height ratio of 1.45:1) with area block- ages between 1.6 and 20% were also tested in each test section configuration. The plates were mounted normal to the airstream with a 2 mm ground clearance gap at an axial station 0.66 equivalent test section diameters from the start of the test section (approximately where the f ront of a test vehicle would be located). Plate base pressures and wall and ceiling pressures were measured.
T 6~8 -
Z05
II t q- 4165 Overall Length
_ 1055 _L 1790 - 2 - - ~
,R 152 (TYP.)
- 4 - i
x, .~l j I 1805
. 5 k ;5,0
.I. o 1320 !
I I
R 3 0 ~
±
1 0 ~
8!2 I R 152 (TYp)
Width 1 I -1 Fig. 2. MIRA car m o d e l for blockage study. All dimensions in ram.
132
0.2, 0 .25 And 0.3 Scale Models
0.3 Scale Model in 0.2 Scale Slotted Wall Wind Tunnel
Fig. 3. MIRA car scale models.
The full scale MIRA car was tested by MIRA, Volvo and the German-- Dutch Wind Tunnel (DNW) in the 6 X 6, 8 X 6 and 9.5 X 9.5 m test sections at DNW and represented 5.1, 3.9 and 2.1% area blockage, respectively. The results of these tests were obtained and analyzed to produce a corrected set of "reference" pressure coefficients by linearly extrapolating the results of the three test section sizes (tap by tap) to a zero blockage or infinite test section condition. This set of data was used in subsequent analysis to deter- mine the degree of blockage present in each of the scale model tests. It is important to note that even the data in the 9.5 X 9.5 m test section required a blockage correction of about 1%. The potential flow model discussed in Section 3 confirmed the magnitude of this correction.
3. Description of blockage evaluation techniques
3.1. Comparison with reference data The comparison between reference and solid and slotted wall wind tunnel
pressure data sets was made by performing a linear regression analysis on a
133
velocity basis. Thus for tap number i, the normalized speed was calculated using
yi - (I - Cp ) In
V~
for both data sets. Linear regression was used to minimize the expression
N
[(1 - C p r e f i ) ½ - A 2 (1 - Cpi)l/2] 2 i= l
The value of A2 can be expressed as a reference pressure or q correction.
qc _ 1 - C p ~ _ 1
q 1 - Cpci A
where the subscript c indicates the deduced corrected value. A measure of the goodness of fit of the linear assumption is given by
N 1/2
Oep = N-1 iffi I
The total acp may include the effect of systematic trends such as axial pressure gradients expected in solid wall test sections. Therefore it is useful to examine individual differences
ei = Cpc~- Cpref/
3.2. Potential f low modelling o f a vehicle In order to evaluate the blockage in a solid wall facility a simple potential
f low model was developed to simulate the inviscid f low outside the separated flow regions around the vehicle and outside the test section surface bound- ary layers. The potential f low model, similar to that suggested by Hacket t and Wilsden [11], consisted of an axially aligned point source and sink pair of equal strength, superimposed on a uniform flow, to represent a solid body in the flow. A second point source was used to simulate the wake displace- ment. Lift and side force induced f low angles can be simulated using horse- shoe vortices. They have not been included in the present analysis because most o f the results to be discussed are for zero yaw and the lift force gener- ated by the models is small at zero yaw. All the singularities used are du- plicated beneath the ground plane (test section floor) to provide the ground influence. For rectangular test sections, the boundary condit ions at the other walls can be met by providing an infinite number of reflections. Five layers of singularities were modeled exactly and the effects of the remainder were modeled using a source sheet for each singularity plane. This distribution of singularities is illustrated in Fig. 4. Equations were derived for the com-
134
Source Sheet
/ / /
1 1 o o o o o o
Wind Tunnel Walls
Body j 8tnoularlty
o " * ( ~ o o o
Reflection
o o o o o o
/ / / j
/ / /
/
~ Pllno
Fig. 4. Ar rangement of source singularities.
putat ion of the three velocity components at any point within the test section.
The wall "interference veloci ty" is the velocity increment or perturbation in the flow caused by the presence of the walls and expressed as a fraction of the freestream velocity. This velocity can be calculated at any point by including only the contributions of the reflections and not the body singular- ities or their ground images. The distribution of interference velocities was relatively uniform over a plane normal to the wind axis but showed a non- uniform axial distribution also reported in ref. 11. In order to correct the force data an average correction over the length of the body can be used. For correcting vehicle surface pressures either an average correction can be used or more appropriately an axially varying correction could be used [ 6, 11 ].
An initial approach to the selection of the singularities was to match the vehicle geometry. The strength and separation of the source--sink pair were chosen such tha t the frontal area and length of the ovoid matched those of the vehicle to be simulated. The wake strength was based on the drag co- efficient and the momentum deficit area of the wake. After some initial investigations the wake source was chosen to coincide with the body "sink". The singularities were placed along the centerline of the test section at an elevation equal to the height of the centroid of the reference frontal area of the vehicle.
135
The adequacy of using three point singularities and their reflections to model the inviscid far field of a vehicle is supported by the comparison with a more complete simulation using a panel method [12]. In this method 196 source sheet panels were nsed to describe the car shape, as illustrated in Fig. 5, and a further 365 source sheet panels were used to describe the test section walls. The ceiling centerline pressure distribution, for an 8.3% area blockage and a drag coefficient of 0.28 is also shown in Fig. 5. Even though the comparison is quite good, neither model takes into account the separa- tion regions of the vehicle nor the viscous effect of the vehicle's pressure field on the test section boundary layers.
To overcome these limitations experimental ceiling pressure distributions were used to determine the blockage interference. The strengths and axial locations of the singularities were chosen through an iterative procedure to match three measured values of pressure on the ceiling, one at the peak pressure, one at the asymptot ic value downstream and one near the front of the vehicle. Another computer program was writ ten to compute the re- sultant ovoid bodies.
0.1
o ~ 0 .0
t ~
~ - 0 . 1
o Ovoid Model - - Pane l M o d a l
- 0 . 2 I I i I I I - 6 . 0 - 4 . 0 - 2 . 0 0 .0 2 .0 4.0 6.0 8.0
X (m)
t T i i i [iL~ t ~ t . J
" !
z
3.0
Fig. 5. Comparison of panel method and ovoid model (8.3% blockage).
136
4. Flat plate measurements
The usefulness o f fiat plates for blockage determination has already been shown in the literature [1, 2] and can dramatically illustrate the effec- tiveness o f the slotted walls. A total of ten flat plates were tested in the solid and slotted wall test sections to cover a range of area blockages from 1.6 to 20.0%. The measured base pressures as a function of area blockage are shown in Fig. 6. The solid walls and 12% OAR slotted walls show significant block- age. The 30% OAR walls reduce the interference effects to near zero for area blockages less than 15%. Four measurements in an open jet facility are also shown and indicate a slightly "open" correction required for area blockages above 10% (corrected pressure coefficients are larger in magnitude than measured pressure coefficients).
The ceiling pressure signatures were matched using the ovoid fitting program to derive the properties of equivalent ovoids for each flat plate. The success at matching the signatures is illustrated in Fig. 7. One can consider that the ovoid represents the combined blockage of the flat plate and its
-1 .8
-1.8
- 1.4 c%
-1 .2 .
Fiat - 1 ~ Plate B ~ e Preeewe
-0 .8
- 0 .0
-0 .4
-0 .2 0.0
LEGEND
8¥mbol ~ Deacr~k~n Mese~ed Predated OAR
X 0 | Messured~ • 12 I ~ W ~ d • 30 TunnY•
100, 0 (314
[] A~" .~..__.
Teet Section /
Area = A
1.45
. o D I~ ~ v - Q J l l A
Y []
¢
0~)5 0.10 0.18 0.20 Blockage Area Ratio, S/A
Fig. 6. Flat plate base pressures.
137
separation bubble. The mean ratio of the ovoid-to-plate area for all but the largest and smallest plates is 2 .26 with a standard deviation of 0.14. The "wall interference" velocity along the centerline of the test section at an elevation equal to the half-height of each plate was calculated using the procedure described in Section 3.2. The average interference velocity over the length o f the ovoid was used to determine a blockage correction for the plate base pressure coefficients. The corrected values are shown in Fig. 6 as squares. It can be seen that the influence of the blockage on the data has been virtually removed using the relatively simple model.
The suitability of using the flat plate results to simulate vehicles at zero yaw can be seen from Fig. 8. The far field pressures generated at the ceiling by a flat plate and a vehicle are quite similar. A flat plate with an area blockage of approximately 3.7% yields the same peak pressure coefficient as a vehicle with an area blockage of 8.3%. The asymptotic value of the wake pressure coefficient differs in magnitude reflecting the difference in the drag.
Fig. 7. Flat plate measured (symbols) and ovoid-matched (lines) ceiling pressures in solid wall wind tunnel.
138
S = Flat Plate Area A =Test Section Area
0
A C p
-0.1
-0.2
-0.3
0 X/Lcar - t . 0 -0.5 0.5 1.0 1.5
I= . . I ~ = I ] S/A O O <---.-0.016
~ I R A Car (SIA = 0.083)
"Equivalent" Flat Plate
Fig. 8. Measured solid wall ceil ing pressures: f lat plates and M I R A car.
5. MIRA model measurements
Each of the three MIRA car models was placed in the solid wall, 12 and 30% OAR slotted wall test sections. The uncorrected surface pressures on each vehicle are shown in Figs. 9--11 at zero yaw and in Fig. 12 at -20 ° yaw in the 30% OAR slotted wall test section. The corrected DNW "reference data" , as defined in Section 2, are also plotted in each figure. Several quali- tative observations can be made. The solid wall results show a consistent blockage error that increases with model size. Both the 12 and 30% OAR slotted wall results agree better. For the 30% OAR slotted wall test section the level of agreement at - 20 ° yaw is similar to the zero yaw case. Some of the apparent discrepancies have been identified as model-specific variations. For example, the pressures on the front of the vehicle at the beltline do not agree well with the DNW results for either the 0.2 or 0.3 scale models. However, the 0.25 scale results agree well. Further examination of the results indicated that the measured pressure coefficients in this region of the vehicle are extremely sensitive to tap position. Figure 13 shows t h e variation of pressure coefficient with tap position on a vertical line through the center of the vehicle. The beltline (tap 1) occurs in the region of maximum pressure gradient. Other regions of large pressure gradients also showed differences between the results.
A least-squares method as described in Section 3.1 was used to quantify
139
. . . . \
- - D N N R E F E R E N C E + 0 . 2 0 B C A L E s 0 0 ~ ; O A R R U N S I 0 $ ? Y A N I 0 . 0 D G 8
0 . 2 0 8 C A L E ~ 1 2 ~ O A R 1 4 7 1 . 0 0 0 . 2 0 S C A L E 5 3 0 ~ ; O A R 1 8 2
F i g . 9 . M e a s u r e d p r e s s u r e s : f u l l s c a l e v s . 0 . 2 0 s c a l e M I R A c a r .
1 . 0
- - D N N R E F E R E N C E + 0 . 2 5 S C A L E 5 0 0 ~ O A R R U N S I 1 0 5 X 0 . 2 5 8 C A L E ~ 1 2 ~ O A R 1 5 1 0 0 . 2 5 S C A L E 5 3 0 ~ O A R 1 7 3
1 . 0 0 . 5 0 . 0 O . S L E F T S I D E X / L T O P S U R F A C E
Fig. 10. Measured pressures: full scale vs. 0.25 scale MIRA car.
. 0
140
1 0
- - D N W R E F E R E N C E + 0 . 3 0 8 C A L E ~ 0 0 ~ O A R R U N S I l l l Y A W l O . O D G 5 X 0 . 3 0 8 C A L E ~ 1 2 % O A R 1 5 3 0 0 . 3 0 8 C A L E ~ 3 0 % O A R 1 0 4
0 5
0 0
- 0 5 P
- I 0
- 1 5
- 2 0 I I . 0
I
i
~ - - ~ - - ~ . . . . . . . . . . . . . . ; : X X X x ~ ~ ~J~ (~ I~l ~ l ~ / I I ~_
I -t- + + + Jr -t-
i + ,,
+ ,,
L E F T S I D E X / L T O P S U R F A C E
. O
Fig. 11. Measured pressures: full scale vs. 0 .30 scale MIRA car.
1 . 0
0 , 5
0 . 0
- 0 . 5 C P
- 1 . 0
- 1 . 5
- 2 . 0
i / . . . . \ - - D N W R E F E R E N C E + 0 . 2 0 8 C A L E ~ 3 0 % O A R R U N 8 1 1 7 2 Y A W l - 2 0 . 0 D G 5 X 0 . 2 5 8 C A L E ~ 3 0 % O A R t 8 3 0 0 . 3 0 8 C A L E ~ 3 0 % o f i g 1 8 4
. 0 0 . 5 0 . 0 0 . 5 1 . 0
L E F T S I D E X / L T O P 8 U R F A C E
Fig. 12. Measured pressures at y a w .
1 4 1
the comparison of the present results with the "reference" data. For each comparison, taps that appeared to be sensitive to position or pitch of the model were excluded. In this way a q correction was computed for each model--wall configuration that was tested. The results are shown in Table 1. On each line of the table the open area ratio (OAR), test section configura- tion, model scale and solid blockage ratio are given. The number of taps (from a total of 76) used in the analysis and the mean q correction are also listed. The Ocp is a measure of the remaining differences after the correction has been applied. Some disagreement is expected because of differences between models. The reference data were derived from the full scale vehicle test results (including the 6 × 6 m test section results) and therefore the agreement between the reference data and the data from the 6 × 6 m DNW tests is good. The lowest value of Ocp for the DSMA solid wall tests occurs for the 0.25 scale model and suggests that this model most closely resembles the full scale vehicle. The corrections versus solid blockage ratio are shown graphically in Fig. 14. Results from the DNW pressure tests are consistent with the DSMA tests. The 30% OAR slotted wall results indicate that a
-qymbol D e s c r i p t i o n
0 0.2 Sca le ~, 0 .25 S c a l e Q 0 .3 S c i l e
I - 1 , 5
g
400 - - -
.......... G~O 5
2oo
t i - 1.0 - 0 . 5 0
-201
...f.~'~" ..... -400 -
• ~" ~o 3~
"':"~*""~ ........ "~ 30-eO0-
_ _ _ ~ 2 1
-~- . I 3 3 / I , , ~ " 3 2 #! I I ; ,
G.r . . . . . . . . 1.o
I . . . . . . . . . ~ 3 3
C p
Fig. 13 . D i s t r i b u t i o n o f pressures o n f r o n t o f vehic le .
142
T A B L E 1
Resul ts o f l inear regress ion analysis , zero yaw
Wall Fac i l i ty Model Blockage N u m b e r O A R scale (%) of (%) taps
q co r r ec t i on
a c p
0 DNW 9.5 1.0 2.06 0 D N W 8 X 6 1.0 3.87 0 D N W 6 X 6 1.0 5 .16
Fig. 14 . q c o r r e c t i o n vs. area b l o c k a g e for M I R A veh i c l e .
143
correction of approximately 3% is required for the 0.3 scale car in the 0.2 scale test section. This compares with a 2.3% correction required for the much larger 6 × 6 and 8 × 6 m solid wall tests at DNW. There is no apparent required correction for the 0.2 scale vehicle in the 30% OAR test section.
The residual differences, el, are plotted as a function of axial position for several cases in Fig. 15. The differences for the 6 × 6 m DNW results show that there is an axial static pressure gradient which is known to exist in solid parallel-walled test sections. The effect is even more pronounced in the 13.0% blockage (0.25 scale model) results. Additional scatter may be caused by differences between models. For the 30% OAR slotted wall test section there is no axial static pressure gradient but some scatter. The largest dif- ferences are less than 0.1 in magnitude and usually occur in areas where the pressure coefficients have large magnitudes or large spatial gradients.
0.05 To DNW exam Solid Wall Wind Tunnel (5.2% Blockage) p ° o o
o o o 1.0 o ~ , ~ . . . . 0.8 ,~
0.2 0.~ ~ 0'.0 c," o~ ,~_ o ~ o ~ ~ l 0 L o c o l i l n , X I L
-0.05 0.10
0.05
C P L s - Cpre f 0
-0.05
DSMA Solid Well Wind Tunnel (13.0% Blockage)
o o o
~ o o o 1.0
o 0 0 0 0 0 0
0,2 oo 0!4"o I I Axial O.g 0.8 o co o Location, X I L
Oo 8 % o ° o o o o o
o
0.10 T D$MA 30~ OAR 8lotted Well Wild Tunnel (13.0~ Blockage)
0.05 ~ _ o o o
1" o Co ° ° o
o ,°o c o °oo oo.O ~ o o ~2 o o'.4 o~e 0~0 o~'.0 Axlel
o - - O o ~ Location, X / L o o o c o o o o
- 0 . 0 5 ~c o
Fig. 15. Residual differences in pressure coefficients after blockage correction is applied.
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145
The ovoid matching program was used to predict required corrections for the solid wall DSMA tests. The derived body shapes that provide the best match to ceiling pressure signatures are shown in Fig. 16. The ratios of ovoid area to vehicle frontal area are 1.02, 1.06 and 1.09 for the 0.2, 0.25 and 0.3 scale vehicles, respectively. The ovoid lengths are 1.07, 1.04 and 0.97 times the vehicle length for the 0.2, 0.25 and 0.3 scale vehicles, re- spectively. The wake sizes are as much as 140% larger than that predicted using a momen tum balance and the vehicle drag. This is a result of attribut- ing all viscous effects, including induced changes in wall boundary layers, to the vehicle wake source. The deduced correction velocities are shown in Fig. 17. The correction velocity predicted using an ovoid matching the length, frontal area and drag of the vehicle rather than the measured pressure signature is also shown. The correction is under-predicted using this geo- metric method. By using the average correction velocity over the ovoid length a q correction was derived for each DSMA solid wall test configura- tion. They are shown in Fig. 14 and agree well with those derived by direct comparison with reference data.
Symbol Meaeured Relults
• Solid Wills
0 30~ OAR 8lotted Wll l l
Symbol Predl~tione Solid WeBs - Bseed on
m t ~ o~ oea.. cD 8o.d Wslle - Sued on
"Free Air B- ~ll~ed on ----m hitch of sOlid Oq~g Cl
0"05 I
.~------~--.0.25 n ~ 0.75 0 1.0 o ho "'~" .,."_-a" o "-t
o I ~ x o / / _ o
I - " , " o . / o . . . . . \ " - . . J ' ~ J ~ , - - - .
- 0 . 0 5 . ,., -
_ o , 1 o .
-0.15- ~ Air Flow
- 0 , 2 0 - "
X/LTs
Fig. 18. Test section ceiling pressures at zero yaw. 8.3% blockage.
146
Symbol Measm'ed Results
• Solid Walls
0 30% OAR Slotted Willis
Symbol Predictions Solid Wi l ls - Based on
match of ~ CD
Solid wilnil - Balled on body m~metr/
"Freil A i r ' - Based on 0.1_ I I - - - - I match of solid ceiling C;
Fig. 19. Tes t s ec t ion cei l ing pressures at ze ro yaw. 18.7% blockage.
The derived ovoid representations of the vehicle were used to predict pressure coefficients at the wall location in "free air" (no wall constraints). These results are shown in Figs. 18 and 19 along with measured pressure coefficients on the centerline slat in the 30% OAR test section for two model sizes. These results indicate that most of the measured pressure signature is caused by the vehicle pressure field and not interference effects. The measured signatures in the solid wall test section are also shown with the matched signatures from the ovoid model.
6. Conclusions
It has been shown that flat plates can be used to study the interference effects of walls for automotive testing. The influence of the plates on the walls and vice versa can be analyzed using similar techniques to those used for vehicle tests.
147
A wall pressure signature analysis method has been used successfully to estimate the interference effects of solid wall test sections for vehicle tests at solid blockages up to 18.7%. The method uses a set of point sources and sinks and their images to simulate the flow conditions outside the region of the model and its separated flows. The analysis showed that a q correction that varied axially in the test section was appropriate for correction of pressure coefficient data. A "buoyancy correct ion" could be used partially to account for this variation when correcting force data.
Slotted wall test sections with open-area-ratios (OAR) of 12 and 30% were used to measure surface pressures on car models at up to 18.7% blockage. These results were compared with reference pressure data derived from measurements on a full scale car shape in three large test sections at DNW in the Netherlands. Blockage effects in the form of reference dynamic pressure, q, corrections were deduced and it was shown that the corrections were very small and comparable to solid wall results obtained at much lower blockages. For a properly scaled vehicle (8.3% blockage) in a 30% OAR test section the wall interference was negligible. The results for a larger car (18.7% blockage) in the existing 30% OAR test section showed that a small q correction was necessary. By properly choosing the open area ratio of the slotted walls and the length of the test section, the wall interference for the 0.3 scale car (18.7% blockage) could be reduced.
Acknowledgments
This project has been supported by the National Research Council of Canada (NRCC) under their Program for Industry/Laboratory Projects (PILP, Arrangement No. CA910-4-0028/635). The assistance of NRCC personnel, particularly M. Mokry of the High Speed Aerodynamics Section of the National Aeronautical Establishment, during the course of this project is gratefully acknowledged. The authors are indebted to their colleagues at DSMA for useful discussions and particularly to L. Grant who performed the wind tunnel tests and much of the data analysis. The reference pressure data set was derived from tests undertaken by MIRA, DNW and Volvo at the DNW wind tunnel in the Netherlands.
References
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3 C.F. Cowdry, Application of Maskell's theory of wind tunnel blockage to very large solid models, National Physical Laboratory (NPL), Aero Report No. 1247, 1967.
148
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