1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243TO PLACE A DOCUMENT
3、 ORDER; (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.orgCopyright 1994 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001INFORMATIONREPORTAn American National StandardJ2071REV.JUN94Issued 1990-
4、03Revised 1994-06Superseding J2071 MAR90AERODYNAMIC TESTING OF ROAD VEHICLES - OPEN THROAT WIND TUNNEL ADJUSTMENTForewordThis document has also changed to comply with the new SAE Technical Standards Board format. Thedocument title has also changed.1. ScopeAs a simulation of road driving, wind tunnel
5、 testing of full-size vehicles produces certain errors in theaerodynamic forces, aerodynamic moments, and surface pressures. The magnitude of these errors, ingeneral, depends on the following:a. Flow qualityb. Determination of the reference dynamic pressurec. Wind tunnel floor boundary layerd. Test
6、section geometry and position of the car within that geometrye. Shape of the vehiclef. Blockage ratio: The ratio of the cross-sectional area of the vehicle to the cross-sectional area of thewind tunnel nozzleg. Wheel rotationh. Internal flow in the modelThe SAE Standards Committee, Open Throat Wind
7、Tunnel Adjustments had as a goal to document theknowledge of the influence of model interference on wind tunnel test results for automotive open jet windtunnels. This document contains the following information related to this subject:a. Design data of open throat wind tunnelsb. A summary of publish
8、ed and unpublished test datac. Documentation and theoretical explanation of various blockage correction procedures for automotivetestsd. Critical evaluation of blockage correction procedures, especially in relation to other influences, such astest section geometry, position of the car, floor boundar
9、y layer, etc.e. Recommendation of a calibration procedure to determine the effect of blockage and other influencesin each individual wind tunnelAn initial goal of the committee, to recommend a well proven correction procedure for automotive open jet windtunnels based on blockage theory (Figure 1), c
10、ould not be established at this time. The reason is that, besidesblockage, other factors, such as test section geometry, are at least as influential as pure blockage. As theseinfluential parameters are wind tunnel specific, a general valid adjustment procedure is presently not available.SAE J2071 Re
11、vised JUN94-2-FIGURE 1PURE MODEL SIZE INFLUENCE2. References2.1 Applicable PublicationsThe following publications form a part of the specification to the extent specifiedherein. Unless otherwise indicated the lastest revision of SAE publications shall apply.2.1.1 SAE PUBLICATIONSAvailable from SAE,
12、400 Commonwealth Drive, Warrendale, PA 15096-0001.1. Ludvigsen, K.E.Automotive Aerodynamic Research Over Past 50 Years in Germany, Great Britain, Italy, United States,and Other CountriesSAE Paper 700035, 19702. Buchheim, R. et al.Comparison Tests Between Major European Automotive Wind Tunnels.SAE Pa
13、per 800140, Detroit, 19803. Buchheim, R. et al.Comparison Tests Between Major European and North American Automotive Wind TunnelsSAE Paper 830301, Detroit, 1983SAE J2071 Revised JUN94-3-4. Cogotti, A. et al.Comparison Test Between Some Full-Scale European Automotive Wind Tunnels - PininfarinaReferen
14、ce CarSAE Paper 800139, Detroit, 19805. Costelli, A. et al.FIAT Research Center Reference Car: Correlation Tests Between Four Full Scale European WindTunnels and RoadSAE Paper 810187, Detroit, 19816. Carr, G.W., Stapleford, W.R.Blockage Effects in Automotive Wind-Tunnel TestingSAE Paper 860093/19867
15、. Mercker, E.General Consideration About Blockage Correction in Open Jet Wind TunnelsSAE Subcommittee No. 9 - Communication (1987)8. Janssen, L.J., Domeland, P., Lindener, N.The New BMW Acoustic Wind TunnelPaper planned for SAE Congress, Detroit, February 19909. Janssen, L.J., Lindener, N., Mullenba
16、ch, P., VAGT, J.-D.Measurement of Tunnel Speed and Static Reference Pressure in Open Jet Automotive Wind TunnelsPaper planned for SAE Congress, Detroit, February 19902.1.2 OTHER PUBLICATIONS1. Konig-Fachsenfeld, R.Aerodynamik des Kraftfahrzeugs Umschau-Verlag, Frankfurt a.M.2. Kramer, C. et al.Wind
17、Tunnels for Industrial AerodynamicsJ. Wind Engineering and Industrial Aerodynamics 16 (1984), pp 2252643. Lock, C.N.H.The Interference of a Wind Tunnel on a Symmetrical BodyARC, R therefore, the space between the rear end of the model and the collector intakearea is decreased. This will be discussed
18、 later in more detail.In a comparison paper by Cooper (see 2.1.2 (15) , 1:10 scale trucks were tested in closed and open windtunnels. The two trucks used in the tests were well detailed, each having both a high and a low dragconfiguration. For the open tunnel, the following correction was applied to
19、 the data:(Eq. 15)whereas the data of the closed tunnels were corrected by the formula:(Eq. 16)where:CD = Drag coefficient in body axis coordinatesCDu = Uncorrected drag coefficientCDb = Drag increment due to wake buoyancy = Yaw angleA = Model frontal areaA2 = Part of nozzle area above ground planeC
20、D C( Du0.25 CDb)cos (1 0.5 AA2)+=CD C( Du CDb)cos (1 2 AA2)+=SAE J2071 Revised JUN94-22-FIGURE 11CORRECTION OF WAKE PRESSURE OF A 60 DEGREE ANGLED PLATE IN AN OPEN JET TEST SECTION AFTER REFERENCE 2.1.2 (14)SAE J2071 Revised JUN94-23-FIGURE 12BLOCKAGE CORRECTION METHODS VERSUS BLOCKAGE AREA RATIO AF
21、TER REFERENCE 2.1.1 (3)This correction was obtained from References 2.1.2 (11) and 2.1.2 (16). The results of the measurements withtwo models are shown in Figure 13. In almost all the configurations tested, the open jet showed the lowestvalues. Even when the values are adjusted for blockage and buoy
22、ancy, using the equations, the data spreadreduces to only 15% of the mean values.In experiments by Frimberger and Pucher (see 2.1.2 (17) a set of sharp edged cubes was tested in eight openthroat wind tunnels to investigate the influence of blockage. Only pressures in specific cross sections weremeas
23、ured. The main results were:a. The front faces of the cubes were almost unaffected by blockage.b. On all other faces the pressures measured were too low.c. The tendency of pressure change with increasing blockage is different for each wind tunnel.d. The tendency of pressure change with increasing bl
24、ockage is different for each face of the cubes.e. Correction factors for pressure and drag coefficients derived from the measurements are different(Figure 14).f. The number of parameters, which varied in the wind tunnels, was too large to assign single influencesto specified parameters.The results o
25、f this section are discussed in Section 5.SAE J2071 Revised JUN94-24-FIGURE 13DRAG COEFFICIENTS OF 1:10 SCALE TRUCK MODELS IN DIFFERENT WIND TUNNELS AFTER REFERENCE 2.1.2 (15)SAE J2071 Revised JUN94-25-FIGURE 14MEAN PRESSURE IN SPECIFIC LINES AS A FUNCTION OF BLOCKAGE IN DIFFERENT WIND TUNNELS AFTER
26、 REFERENCE 2.1.2 (17)SAE J2071 Revised JUN94-26-4.3 Influence of Test Section Design4.3.1 GENERAL CONSIDERATIONSThe quality of an open jet test section is mainly determined by the sizing of thecollector with respect to the test section dimensions. By turbulent exchange at the free boundaries of the
27、jetdischarged by the wind tunnel nozzle, turbulent mixing zones are established, the width of which increasewith increasing jet path length. Consequently, the jet velocity profile in the mixing zones flattens withincreasing length of the test section, and the portion of the jet cross section contain
28、ing the volume flowdischarged by the nozzle increases with increasing distance between nozzle and collector. The size of thecollector should fit this cross section. Furthermore, the cross-sectional shape should be appropriate and itshould be taken into account that the jet discharged by a rectangula
29、r nozzle becomes round due to turbulentdiffusion and that this rounding effect increases with increasing jet path length. Therefore, for an openautomotive wind tunnel, a collector with broken upper edges may fit better than a collector with a rectangularcross section. Of assistance in designing a co
30、llector may be a jet calculation described by Regenscheit (see2.1.2 (18) and Kramer et al. (see 2.1.2 (2). In this simple calculation, the friction at the ground plate is nottaken into account because the shear stresses applied to the jet, due to the turbulent mixing, are of a farhigher order of mag
31、nitude. The collector cross section should be determined in such a way that the dividingstreamline, separating the volume flow entering the collector from the volume flow recirculating in the plenumsurrounding the test section, is in a stable position on the rounded leading edge of the collector. Th
32、isprocedure was described in detail by Kramer et al. (see 2.1.2 (19).The curvature of the leading edge of the collector is especially influential in the investigation of models undernonsymmetrical flow conditions. In this case, also, the position of the dividing streamline on the collectorleading ed
33、ge should be stable (Kramer and Gerhardt) (see 2.1.2 (20).For test sections that are short related to the nozzle dimension, the velocity profile in the mixing zone at theposition of the collector still has a strong lateral gradient. Due to the steep gradient, a small misalignment ofthe collector pos
34、ition and/or the curvature of the collector leading edge can cause rather strong changes inthe static pressure distribution along the test section. Therefore, a carefully designed collector is required.Because the entrainment flow for a short test section is relatively low, the volume flow recircula
35、ting in theplenum surrounding the open jet is relatively small. Therefore, for such a short test section, a relatively smallplenum seems to be sufficient.If full-scale cars have to be tested, a certain minimum length of the test section is required. Therefore, windtunnels with smaller nozzle cross s
36、ections have a larger ratio of open jet length related to the nozzledimensions. Also, the ratio of the entrained volume flow to the volume flow discharged by the nozzle is largerfor those wind tunnels with relatively small nozzles. The open jet entrainment depends on the ratio of jet freecircumferen
37、ce to the jet cross section, which is larger for a small nozzle than for a large one at the sameopen jet length. Therefore, for full-size wind tunnels with small nozzles, the mixing zone at the end of the testsection, compared to the size of the test object, is much wider. This leads to a flatter to
38、tal pressure gradientin the mixing zone at the collector distance. Consequently, the lateral variation of the dividing streamline,separting the flow into the collector from the recirculating flow, becomes less critical. From this it may beconcluded that, for a large test section length in comparison
39、 to the nozzle dimension, a larger collector and aless sophisticated collector leading edge design may be appropriate. The recirculating volume flow,however, related to the volume flow discharged by the nozzle, increases noticeably. Therefore, such longtest sections require much larger relative dime
40、nsions of the surrounding plenum.4.3.2 EXPERIMENTSV. Schulz-Hausmann and Vagt (see 2.1.2 (21) performed experiments to evaluate theinfluence of the test section design. By varying the test section length by moving the collector upstream, theinfluence on the static pressure distribution in the longit
41、udinal direction could be demonstrated. Figure 15shows this correlation for a collector/nozzle ratio AC/AN = 1.96 with the test section length as parameter,which is given in dimensionless form LT/DN, where DN = 4 AN/(2BN + 2HN), the hydraulic diameter.SAE J2071 Revised JUN94-27-FIGURE 15STATIC PRESS
42、URE DISTRIBUTION (EMPTY TEST SECTION) AFTER REFERENCE 2.1.2 (21)In a second step, the collector/nozzle ratio AC/AN was varied. Figure 16 shows, among others, some testresults for two identical models of different scale. Obviously, with a sufficient test section length, the resultsbecome independent
43、of the nozzle collector ratio and the blockage ratio. In principle, for each test sectionlength (more precisely, for each distance between rear end of model and collector), a nozzle/collector ratiocan be defined where the test results are brought to an optimum (CD/CDref = 1). But due to the highgrad
44、ients of the slopes in the neighborhood of this optimum, a variety of results is easily introduced.Furthermore, the results show a clear blockage dependency for small test section lengths and small nozzlecollector ratios. This is probably due to the fact that the jet of an open test section expands
45、differently with orwithout the model placed in the test section, creating different recirculation and entrainment flow in thesurrounding plenum chamber.Vagt (see 2.1.2 (22) also measured the drag of four thin flat square plates in a full-size wind tunnel. Duringthis test series, the blockage area ra
46、tio was varied (A/AN = 4.48%, 5.43%, 7.01%, and 8.79%). Although theplate edges were rounded, no Reynolds number effect could be detected between velocities of 10 m/s andabout 38 m/s. Figure 17 shows results for a fixed collector area. As the pressure gradient in that wind tunnelis practically zero
47、and the wake formation for the three smaller plates is obviously independent of collectorsize, it is quite likely that the aproximation given by the solid line represents a blockage effect.Some concern exists for CDo, which was evaluated by linear extrapolation to zero area blockage. Therefore,in a
48、strict sense, there is some uncertainty in the absolute value. This is represented by the upper and lowerboundaries.For the largest plate (A/AN = 8.79%), the wake extends into the influencing region of the collector and, thus,the result is strongly dependent on the collector size. The effect of the
49、collector, which is only present for thelargest plate, is shown, as an example, by the vertical arrow.Thus, in general, a possible combined blockage collector influence given by the broken line can beestimated.SAE J2071 Revised JUN94-28-Gerhardt and Kramer (see 2.1.2 (27) carried out experiments with models resembling the Ford-Transit.Their experiments also show the influence of test section length and position of the model in the test section.The experiments were carried out in the Gttingen-type wind tunnel of the Fachhochschule Aachen. Therat
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