1、i. NASA TM-X 56023 c.1 NASA TM X-56023 !,71r - 17 7C 3 OMG REDUCTION OGTAINED BY ROUNDlNG VERTICAL COKVERS ON A BOX-SHAPEI GROUNP VEI-IICLE Edwin J. Saltzmsn and Robert H.Meyer , Jr . MAN COPY: RETURN TO AlWL TECHNJCALLIBRARY, KIRTLAND Am, NM NASA hi compilcd in reference 4. It is rcalizcd. also on
2、:he basis of rcfcrenee 4. lhr the optimum r/w rntio is probably bcfwcea 0.2 rind 0.1 (consid ering the conflicting ccdsfor reduced drzlg and rnximiimvolumc for u given vehicle lcnl squxrc-cornered configuration unci 20 tcsts for thc roundcd c!onfigurition. The dirtn shown were obtainc-d from stop wn
3、tch-specdoinciter readings, tind thus definc tlic totnl drag of the two co?ifi:urritions in an absolute sense. Reynolds numbers tmsetl oil the vehiclc lencth r:ingcrf fron 4.4 i( 10 to 1 .O X IO for the vclocity rnnge of thcse dntn. The sym?,ol itV -+ 0 is the luw-limit trmtive drng obtiiined for th
4、e vehicle for the test tirc prcssues on the surface of thc test runwoy . This triictive drng was 0b:;iincd with a fish-type scalc of 100 LioUnd range. The vchicle was towed ut approxirnntcly 2 niilcs pcr hour during this meesur-Pmcnt. The dashed curve is ifn cxtriipolation of the mensurd low-limit t
5、rctctive drog based on the semiempirical ccuatiorifrom lioerner !ref. 4. ch. 12). At 55 miles per hour, thc configurntion with the rounded corners has n drRg lcwel similar to thnt of the squore-cornered vehicle at approximntely 44 miles per hour. Conversely ,extropolution of the modified (rounded) v
6、ehicle results to higher spccvls shwsthnt at npproximutcly 70 miles per hour Ihc more refined configuretion would have about the sbme drctg as the square-cornered vehicle nt 55 miles per hour. The test van front suspension, though stiffened by auxi!iary helper springs. was flexible enough to allovv
7、some depression of the front of the vehicle during deceleration. Thus the accclcrcmeter sensed the effect of the lowered front of the vehicle, a component of the ecceleration of gravity, in addition to the rate of change of forward velocity. Thus the 3pporent drag, based on the accelerometer outptlt
8、 . was Coo large for both or !he test configurations. Nevertheless. the difference in drng between the two configurations, 8s defined by the accelerometer, is an authen tic backup measurement and confirms the results obtained from the primary stop watch-speedometer method. The incremental. drag diff
9、erences determined by both 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,. The decre.sse in drag. which is ecrodynainic in origin. can lsobe considered as n perccntuge of the acrodynsmic component of driig 4 the square-coxmered vehi cle instead
10、of 8s n percentage of the total drag (i .e., as a perccntflge of the meas ured totnl drag minus the mechanical drag). On the idttcr basis the driig reduction provided by the roundcd vertical cwriers, RS defined by tilt speedomctcr-stoprvatch method. would be about 40 percent at 60 miles per hour. Th
11、is reduction in drag was achieved by sacrificing 1.4 percent in vehicle volumc. Subtracting the extrapolsted tractive drag from the totnl drag and accounting for the thrust from the rotritionnl inertia of wheels and tires also permits ;in aerodynamicdrag coefficient. CD ,t3 be calculated for each co
12、nfigurntian. Rnsed on an area of a 35.3 square feet, which is +hebody cross-sectional area, thc aerodynamic drag coefficient is 1.13 for the square-cornered configuration and 0.68 for the modified configuration The value of 1.13 is significantly higher than the drag coefficient ! (0.86) shown in ref
13、erence 4 for a square-cornered vehicle tested in a wind tunnel. If reference 4 used the box projected frontal area plus the exposed wheel projected area as the reference, about one-fourth of the diffcfence could be Rccounted for. It is suspected that the highcr drag coefficient values CalCUlRted for
14、 the square-cornered vehicle of the prePent study arc caused primarily by the unsealed underbody which would not hsve been simulated by the model reported in reference 4. . 1he present study was limited to the coast-down method of sensing drag, -_- which does not define relative gas consumption, or
15、gas mileage, per se fer the. respective configura:ions. Thus the drag reduction which has been demonstrated -e 6 . e-. 1 I 1. I , . .I / . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I. . i nit photogr:iphs wvn mat111 (luring tests of tictwo conf
16、igurations over II rangeof vciocitics rind with tho cooling vcrnt opm tind chsetl. ihv iclurcsprovidc n rrrilphic oxplanation of tho significi;int tiiffcarcwcc*s in dr;iE. 1;igirrt-s 1 ()(:I) rind 1O(b) .;how results 111iit tirc tyl)ic;il of the cwtirc? hikhwey specti r;iiigv. It is obvious thnt the
17、 square-cornrrcd coiifigurrition (fig. IO(ii) tins -sepnrntg.d flow jirst brhind the front cornvr iind reverse OW. of scirts. from somcwhcre ncor thv micldlo of the vchicln siclcb to ahciid of tho front wticvls. Only the tift one-third to on( -hHlf of Itlo side shows the twginnings of ntt;iched flow
18、 . ihr configuration with t.oundwl vcy-ticcil corncrs (fig. 10(b) )ins ;itt:iciicd flow itiong the side throiighotit the . rvgions 5h(JIVIl Iiy ;he photogriiph. brick to soinc portion of the rcnr roundi.r! corriw. Ii1Tt ptiotof:r,l;bhs with thc c:ooli;ig vent opcn showed the same patterns 11s with t
19、he vcarit closclcxct!itfor the region iinmcdiiitely adjacent to the opcnirig . S;UJlhl AHY A box -sh;rp(d vctiiclc WIIS tcstcd to obt:liri tjoscline drnE data for square-cornered izrourid vrhiclcs such IS tlclivery vans, motor homc?s. nnd trucks. The !);iscline tcsts for the sciu:tre-cc!i.rici.ed vc
20、hjcle were followed by a drng evaluation of the same vchiclc with t-ouridwl vel;tic:il corncrs on both the front and war. The tcsts covcrc:d thc velocity rringc from 30 miles per tiour to 65 miles pcr hour. nnd the Reynolds number rringc was from 3.4 X lo6 to 1 .O X 10 ,based on vchiclc Irmgth. Roun
21、ding the vortical corners 3f the vehicle reduced the total drag tipproxi niatcly 22 i)cr*ccniat the 1owc.r tcst speeds anti approximately 33 percent at the higher test spcecis. On thc basis of the.aerodynamic component of drng. the dccrcase in drag was :it)orit 40 percent ut 60 miles per hour. 7 . I
22、 -. f :. . .!. . . . Id I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-P :J i i , REIERI:X;ClS 1. Flynn, ilarold; and Kyropoulas, Pctcr: Truck Acrodjtnamics. SAE Ircprint 2844. 1961. 2. Kirsch. Jeffrey W.: Gnrg. Siibodh K.; and Hettes. William: Dr
23、ag Rvduction of Bluff Vehicles With Airvunes. SA!: pf:pcr 730686, 1973. , 3. Ritchie. Devc: How To Beat the Ruilt-in Heedwind. Owner Operntor. hlay/Junc 1973. pp. 89-99. 4. tioerner. Sichard F.: Fluid-Cynamic Drag. Pub. by the author (148 Rustced Dr .,!tlidlend Park, N .J .I, 1965. 2. 5. 1,orrebce.
24、E. Eugcnc: Smoll S(:ile Research in Automobi!? Aerodynamics ., SAE ptipcr 660384. 1966. 6. (;ross. Donald S .; and Sekscienski, Willium S.: Some Problems Conccrninc blind Tunnel Testing of Automotive Vvhiclcs. SAE paper 660385. 1966. 7. hhilc. H. G. S .: A lethod of Estim8tir.g Automobile Drag Coeff
25、icients. SAI: Impcr 690189. 1969. 8. Jurner. Thomiis R.: Wind Tunnel lnvestigation of n Ji8-Sc:ilc Automobilc?3lodc.k Ovcr A Ioving-Iic*lt Crvuriti Plane. NASA TN D-4229. 1967. 9. White, R. A. ; orid Korst , li . it .: The Determina!ion of Vehicle Drag Contributions from Cowit-Down Tests. SAE paper
26、720099. 1972. 10. Austin. Thomiis C .; and Hcllman, Knrl H .: Pnsscngcr Car Fuel Economy -Trends and Influencing Factors. SAE paper 730790. 1973. 8 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- ! Figure 1. Currier vthiclc. I Provided by IHSNot for
27、 ResaleNo reproduction or networking permitted without license from IHS-,-,-c 0 Beitring and gwr rcsisttlncc Figure 2. Schematic showing Fources of tractive drag. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- Figure 3. Carrier vehicle with not pla
28、te and supporting structure. E- 2 64 54 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Horsepower increment. (horsepower of van + supporting structure + flat plate) - (horscpowcr of van) 12 8 4 I 0 I I I I I 34 33 42 46 50 54 Vc, mph Figux 4. Compar
29、ison of measured drhg“ incrcmcnt with predicted increment (converted to horsepower). 58 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- Figure 5. Carrier vehicle with aluminum subframc. E-36477 c. ,. G, grt,- .,.-.- -_ Provided by IHSNot for ResaleN
30、o reproduction or networking permitted without license from IHS-,-,-i I E-26577 E-26575 (a) Configuration with square corners; cooling vent 9pen. Fig-Lre 6. Test vehicle. 14 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I:. E-26796 E-26774 ) Config
31、cliation with rounded vertical corners, front and rear; cooling vent closed. Figure 6. Concluded. 15 a-+ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,
32、-Figure 8. Timer board. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-D, square corners 320 -r 1 240 Dt and I tractive drag, /I lb /I Tractive drag / Dt , round vertical corners / -IC- /Reference 4 I 1 I 4 0 10 20 30 40 50 60 vC. mpli Figure 9. Rel
33、ationship of tbtal drag to veiociv obtained by the coast-down method with StODwatch-SRecdometer readings. (The tractive drag does not include the rotational inirtis of wgeels and tires. 1 70 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- .-I (a) Sq
34、uure cornels. E-26717 . . (b) Rourlded vertical corners. . E-26903 Figure 10. Tuft patterns for each configuration at a calibrated speed of 55 miles per hour with the cooling vent closed. 1 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
