Wind tunnel measurements of the drag of two box bodied articulated goods vehicles

Transcription

1 TRANSPRT AND RAD RESEARCH LABRATRY Department f Transprt RRL Cntractr Reprt 23 i Wind tunnel measurements f the drag f tw bx bdied articulated gds vehicles by K P Garry (Cllege f Aernautics, Cranfield Institute f Technlgy) The wrk reprted herein was carded ut under a cntract placed n Cranfield Institute f Technlgy by the Transprt and Rad Research Labratry. The research custmer fr this wrk is Vehicles Standards Engineering Divisin, DTp. This reprt, like thers in the series, is reprduced with the authr's wn text and illustratins. N attempt has been made t prepare a standardised frmat r style f presentatin. Cpyright Cntrller f HMS 199. The views expressed in this Reprt are nt necessarily thse f the Department f Transprt. Extracts frm the text may be reprduced, except fr cmmercial purpses, prvided the surce is acknwledged. Vehicles and Envirnment Divisin Vehicles Grup Transprt and Rad Research Labratry ld Wkingham Rad Crwthrne, Berkshire RG11 6AU 199 ISSN

2 SUMMARY Aerdynamic streamlining f cmmercial vehicles is believed t bth imprve fuel efficiency, by reducing aerdynamic drag, and reduce the dispersin f water spray by limiting the extent f the vehicles' external air flw field. Measurements f drag frm a prgramme f wind tunnel mdel experiments are presented, shwing the effect f different tractrs and f a variety f streamlining devices. Pressures n the bx trailer were measured n mdels in the wind tunnel and at full scale during rad and track tests. These were used t assess the validity f the mdel tests. Prpagatin f spray arund the vehicles was assessed subjectively by studying smke flw beside and behind the mdels in the wind tunnel. Aerdynamic devices that reduced the drag f the vehicles tended t reduce the area arund the vehicles that appeared t be affected by spray. Streamlining the gds vehicles increased the pressure differences alng the sides f the trailer bx bdy. This has implicatins fr the strength f curtain-sided bx vehicles, and prbably indicates that streamlining des nt reduce the aerdynamic frces n ther vehicles travelling clse t r vertaking the bx vehicle. ACKNWLEDGEMENTS Financial supprt fr this prgramme has been prvided by the Department f the Envirnment and Department f Transprt, crdinated by the Transprt and Rad Research Labratry, Crwthrne, Berkshire, under agreement TRR/842/424 - "Imprved aerdynamics fr large articulated rad vehicles". The wrk described in this reprt frms part f the prgramme f the Transprt and Rad Research Labratry and the reprt is published by permissin f the Directr. The authr wuld like t thank Mr Nigel Cwperthwaite wh carried ut the majrity f the experimental wrk, and members f the cntract steering cmmittee fr their assistance during the preparatin f this reprt, in particular Mr Alan Naysmith (TRRL) and Mr Rn Rider (Freight Transprt Assciatin).

3 wnership f the Transprt Research Labratry was transferred frm the Department f Transprt t a subsidiary f the Transprt Research Fundatin n I st April This reprt has been reprduced by permissin f the Cntrller f HMS. Extracts frm the text may be reprduced, except fr cmmercial purpses, prvided the surce is acknwledged.

4 e, CNTENTS SUMMARY INTRDUCTIN EXPERIMENTAL PRGRAMME 2.1 Wind Tunnel Mdels and add-n devices 2.2 Wind Tunnel Facilities 2.3 Measurement Techniques AERDYNAMIC DRAG MEASUREMENTS 3.1 Tractr Units in Islatin 3.2 Tractr-trailer Vehicles Summary f effectiveness f varius devices. DAF 33 with a bx trailer Summary f effectiveness f varius devices. Leyland T45 with a bx trailer 3.3 Discussin f aerdynamic drag measurements SURFACE PRESSURE MEASUREMENTS 4.1 Wind Tunnel Measurements 4.2 Full Scale Measurements Cntainer base pressures Cntainer frebdy pressures 4.3 Discussin f Full Scale/Mdel Measurements BUFFETING AND SPRAY DISPERSAL 5.1 Spray Dispersal 5.2 Buffet Assessment Studies CNCLUSINS REFERENCES APPENDIX A APPENDIX B THE WIND AVERAGED DRAG CEFFICIENT DEFINITIN F SURFACE PRESSURE CEFFICIENT (Cp) APPENDIX C CMPREHENSIVE DRAG MEASUREMENTS AND DETAILS F THE AERDYNAMIC DEVICES USED 4 (C) CRWN CPYRIGHT Extracts frm the text may be reprduced, except fr cmmercial purpses, prvided the surce is acknwledged.

5 i. INTRDUCTIN Interest in the aerdynamic characteristics f heavy cmmercial vehicles (HGVs) has cncentrated n the ecnmic advantages t be gained by imprving fuel ecnmy thrugh reductins in aerdynamic drag. As a result, fundatins fr the design f lw drag HGVs have been established. The aerdynamic features f HGVs that reduce drag are als believed t affect:- (i) the dispersin f water spray generated by the vehicle's tyres, and (2) the buffetting experienced by ther rad users in clse prximity t the vehicle. Bth these effects are assumed t be clsely related t the structure f the vehicle's external air flw field and it is recgnised that streamlining can significantly reduce the size f this regin as well as changing the vehicle's verall aerdynamic characteristics. The Transprt and Rad Research Labratry (TRRL) has supprted an experimental prgramme at the Cllege f Aernautics, Cranfield Institute f Technlgy, using wind tunnel mdel tests t measure the aerdynamic frces n heavy gds vehicles, t measure the surface pressures n a bx semi-trailer f an articulated HGV, t measure the pressure and velcity in the flw field arund the vehicle, and t use flw visualisatin techniques t assess the spray patterns beside and behind the vehicles. It was decided t cncentrate n tw vehicles, Leyland T45 and DAF 33 tractr units, each cupled with a standard 4 ft articulated trailer. The chice f tractr units was made specifically t highlight the imprtance f the aerdynamic characteristics f the tractr n the aerdynamics f the cmplete vehicle; this is discussed in sectin 3.1. Within the framewrk f the verall prgramme, the wind tunnel measurements can be brken dwn as fllws:-

6 (i) aerdynamic frce and mment measurements n bth vehicles fitted with a range f streamlining devices. (ii) cntainer surface pressure measurements n bth vehicles. (iii) external flw field measurements. (iv) flw visualisatin studies f spray dispersal. The wind tunnel prgramme was supplemented by limited full scale smke flw visualisatin tests n the TRRL test track. This enabled a qualitative assessment f the varius add-n devices t be made and served as an imprtant crrelatin exercise. In additin, surface pressure measurements were made n the full scale vehicles t enable the aerdynamic validity f the wind tunnel mdel tests t be assessed. This reprt cncentrates n the effects f varius streamlining devices n the drag f bx bdied articulated HGVs. It includes a qualitative assessment f the effects f these devices n buffeting and n spray patterns arund the vehicles, and a summary f data n the pressure differences n the sides f a bx trailer. These latter are f value in the design f curtain sided gds vehicles. 2. EXPERIMENTAL PRGRAMME 2.1 Wind Tunnel and Add-n Devices The mdels used fr the wind tunnel experiments were i/8th scale reprductins f the Leyland T45 'Radtrain' and DAF 33 tractr units cupled t a Crane Fruehf twin axle semi-trailer with 4' x 8' x 8' bx cntainer, see Figures 1 and 2. The cab f the T45 is mre runded than that f the DAF 33. The mdificatins made t these vehicles in the frm f add-n devices were chsen t reflect the current and anticipated trend in aerdynamic streamlining fr this type f vehicle, with the emphasis n devices mst likely t prevent water spray dispersin. P,

7 ne characteristic feature f the flw arund this type f vehicle is believed t be primarily respnsible fr the high levels f spray dispersin. Flw ver the cab rf results in high pressures n the cntainer frebdy, and cnsequently a dwnflw in the cab-cntainer gap. This flw mixes with that frm underneath the cab and the pressure increases due t the tractr rear axle and ancillaries impeding the flw. Cnsequently the flw mves utwards ver the tractr rear wheels twards the lw pressure area alng the sides f the vehicle. This lateral mvement f air carries with it water drplets brught frm the rad surface by the tyres. These drplets are atmised int a fine spray when they meet the high speed external flw and are dispersed by the vehicle's flw field. The external flw field can carry this mist sideways away frm the vehicle and upwards away frm the rad surface. The prjectin f large drplets f water sideways frm the tyre/rad surface cntact patch is the result f a cmpletely different physical prcess. Therefre, any add-n devices intended t reduce the dwnflw in the cab-cntainer gap r t smth that alng the sides f the vehicle can be expected t have the additinal effect f reducing spray dispersin as well as reducing aerdynamic drag. The add-n devices chsen fr this series f tests can be categrised int three brad grups as fllws:- (i) Streamlining f the cab-cntainer and cntrl f the flw field in the cab-cntainer gap (a) cab rf plate deflectr (b) cab rf 3-D deflectr (c) central gap seal (d) side gap seal (e) hrizntal gap seal (f) cntainer frebdy streamlining. 3

8 (2) Streamlining f the tractr and trailer chassis/wheels with side skirts (a) (b) shrt tractr skirts between the wheels lng tractr skirts cvering the driven wheels. (c) ttal tractr skirts cvering all wheels, including the frnt axle. (d) shrt trailer skirts cvering the side impact guards. (e) partial trailer skirts, nt cvering the trailer wheels. (f) full trailer skirts cvering the trailer wheels. (g) tractr chassis fairing. (3) Base flw cntrl. (a) base seal. (b) battail. Detailed specificatin f each f these devices is given in Cwperthwaite (i) and a summary in Appendix C. 2.2 Wind Tunnel Facilities (i) The 8 ft (2.43 m) x 6 ft (1.8 m) Wind Tunnel. This facility has a clsed return, clsed wrking sectin layut having a maximum flw velcity f 55 metres/secnd (125 mph) at near ambient temperature and pressure. It is equipped with a six cmpnent verhead electr-mechanical balance, data frm which is returned n-line fr subsequent analysis. P. Fr the tests f the cmmercial vehicles the mdel was munted n a 'grund bard plate'. This technique, detailed by the authr 4

9 (2), reduces the influence f the wind tunnel wall bundary layer, and allws the mdel t be yawed relative t the freestream (t simulate crsswind effects) - whilst at the same time munting the mdel thrugh the wheels (which eliminates the interference effects f munting struts). The wheels f the mdel d nt rtate and the grnd plane is fixed. (ii) The 8 ft (2.43 m) x 4 ft (1.2 m) Bundary Layer Wind Tunnel This is a clsed wrking sectin, pen return facility with a maximum flw velcity f apprximately 2 m/sec (45 mph). It is equipped with a micrcmputer cntrlled, 3 axis prbe traversing mechanism, which permits wake surveys t be made within a cntrl vlume 1.9 m x 1.9 m x.6 m. Fr these tests, bundary layer suctin slts were incrprated int the flr f the wind tunnel's 4 ft lng wrking sectin. This enables the mdel t be psitined at varius lcatins upstream f the prbe traverse mechanism, whilst in the same thickness f flr bundary layer. This permits wake surveys t be made at up t 5. bdy lengths dwnstream f the mdel. 2.3 Measurement Technique (i) Aerdynamic frce and mment measurements The 8' x 6' wind tunnel's typical perating speed fr these tests was 45 m/sec, which gives Reynlds numbers (Re, a scaling factr prprtinal t speed x length) f 1.5 x 16, cmpared t that f a full size vehicle at 6 m.p.h, f 5.49 x 16. Measurements f 6 frces and mments were made ver yaw angles in the range ±2 degrees, fllwing SAE recmmended practice (4). In rder t simplify the analysis, the majrity f the data presented in this reprt is in the frm f wind averaged drag (Cv~) as defined by Ingram (3). A summary f the prcedure used t evaluate

10 wind averaged data is given in Appendix A. The analysis cncentrates n drag, being the cmpnent f aerdynamic frce which directly influences fuel efficiency. (ii) Aerdynamic surface pressure measurements The surface pressure at a specific lcatin n the bx cntainer is measured by cnnecting a small static pressure tapping via pneumatic tubing t a differential pressure transducer. This cnnectin is usually made via a Scanivalve R pneumatic cnnectr which enables up t 48 different tappings t be sequentially switched int the same transducer. The lcatin f the 154 pints n the side and frnt f the cntainer at which pressure measurements were made fr this study are shwn in figure 3. T measure pressures n the ther side and the rear bulkhead, the cntainer was reversed. A schematic layut f the systems used fr bth the wind tunnel mdel and the full scale vehicle pressure measurements is given in figures 4 and 5. Essentially the same technique was used in each case, the principal differences being in the data cllectin and cntrl f the scanivalve full scale. b Surface static pressures reveal cnsiderable detail f the flw arund the vehicle and fr simpler interpretatin are presented in the frm f isbar plts. The cnturs in each case are based n a technique f linear interplatin between each pint in the grid f surface pressure tappings shwn in Figure AERDYNAMIC DRAG MEASUREMENTS 3.1 Tractr Units in Islatin The tw cab units chsen fr the prgramme have fundamentally different aerdynamic characteristics. The Leyland T45 Radtrain uses cnsiderable streamlining, and the full scale smke visualisatin shwed that the flw remains attached t the surface arund the frward leading edges. This characteristic ensures that the regin f turbulent flw r 'wake' behind the cab is a minimum 6

11 and the drag f the cab itself is relatively lw. As a cnsequence the degree f shielding this cab ffers t the trailer it tws is reduced and the frward facing areas f the bx cntainer are expsed t the freestream flw, increasing its drag. In cntrast the DAF 33 cab is a much mre aerdynamically bluff design, the flw is seen t separate frm the surface at nearly all the frward facing crners. Cnsequently the wake behind the cab is larger than the cab itself and this effectively shields the cntainer frm the freestream flw. The relative merits f these different appraches t vehicle design rest n the cncept f flw field 'matching' between cab and cntainer which is discussed mre fully by Gilhaus (5) and thers. The interest, in terms f this research prgramme, was t assess the different results btained when using the same 'add-n' devices n the different vehicles. In supprt f this, a series f tests were carried ut n bth tractrs in islatin, fitted with a range f devices, t supplement the very little aerdynamic data that is available t peratrs wh, fr peratinal reasns, ccasinally have t perate their vehicles ' ractr nly'. Measurements were als made f the drag f the tractrs withut add-n aerdynamic devices twing a flatbed semi-trailer. A summary f the results fr bth vehicles is given, see table 1 and figures 6 and 7, in terms f CDA and CD~A as a percentage f the baseline (tractr nly) vehicle. C D is the nn-dimensinal drag cefficient (see belw), A is the mdel reference area, and the subscript WA means wind averaged drag. In bth cases, tractr skirts were seen t reduce wind averaged drag, their effectiveness (with ne exceptin) increasing as the extent f skirt cver is increased. Tractr skirts appear t be marginally mre effective n the DAF 33. Cab rf munted devices gave different results fr each vehicle. n the Leyland T45, bth 3D rf and curved plate deflectrs gave very significant increases in wind averaged 7

12 i! + ~ ~ +, c~ % % q.4 i + ~ ~,-4,-~ i +, , u'~ E-~ ~ c~,-4 L~,,-I ~= ~ u~,'~ un r ~ ~ ~ ~ ~ ~ ~ ~.. ~, ~ ~ ,-.4. ~ -.I" 4, + E-~ c~ C~ %, N N ~ ~, u'~ 4 %,--44 u~! i i ~ 4 + ~ ~ ~ - ~, +, % % c C,4,-4 +,...4 '4 E LN,--4 E-~.). i 1 + i 4,_~ ),-4 "~ a~ r2~ ~ t~ ~:1 N i -~ r~ -d- %,-4,-4 i i i r ~ ~D i ~D + i e ~ -~" ',~1 -.,-I L~.,.4 e.) < N a % ~ e,4. x "~ C3,-~! i i i c,-4 i Pt i + c~ i i i c~ r,.) ~.. ~ ~J N N "~ ~ P~ ~ ~.~ ~ ~ ~ c ~ "~ 4J 4J 4J IJ ~1 }-I.,-4 r-~,--~ ~.,~ c q-.i q-i,-4 ~.u ' ".-~ u~,,-~ 4J ~q ~,~ rj, t ,.C3 +,.~.,-.I,m ~..~ l..l i ~ W '~ + + II C.9.-4.,-I ~-4,-4,-4 ~4,.4 c~ e;

13 drag. As expected this type f device, which disturbed the therwise streamlined flw ver the rf, caused a large cmpnent drag and significantly increased the size f the wake. n the DAF 33 hwever, while the plate deflectr gave the expected drag increase, the 3D deflectr was seen t reduce the wind averaged drag. This is a surprising result, believed t be due t an interactin between the deflectr and the separated shear layer ver the cab rf. These and ther tests n the tractr units in islatin are discussed further by Cwperthwaite (i). The results are given in terms f the prduct CDA t allw fr the different reference areas f the tw tractrs. The drag f the full scale vehicles is D = ½ p V 2 ( C~A )mdel X 8 2 where p is the density f the air, V is the speed f the air flw (which equals the speed f the vehicle in still air), and the factr 82 is t scale frm mdel t full size. At sea level ~ = 1.2 kg/m 3, and the drag f the full scale vehicle is D = 38.4 V 2 (CDA)mdel Newtns where V is the speed in m/s. 3.2 Tractr-Trailer Vehicles T place the results f the tests fr the bx trailers in cntext, table 2 lists the minimum and wind-average drags fr the tractrs in islatin, with and withut cab-rf deflectrs, fr the tractrs with flatbed trailers and fr the tractrs with bx trailers. Aerdynamic drag data fr the mre imprtant f the bx trailer mdel cnfiguratins tested are given in table 3, in terms f CDmlnA and CD~A. Central gap seals and side gap seals, bth f which are intended t stp transverse flw thugh the gap between the tractr cab and the frnt f the bx trailer, prduced similar changes in drag prvided they filled the same fractin f the tractr-trailer gap. Drag data fr the cmplete set f cnfiguratins tested are given in Appendix C, alng with details

14 TABLE 2. MINIMUM AND WIND-AVERAGED DRAGS FR THE TRACTRS AND VARIUS TRACTR-TRAILER CMBINATINS DAF 33 LEYLAND T45 CNFIGURATIN CDE CDminA CDwAA CDE CDminA CDwAA m 2 m 2 m 2 m 2 ISLATED TRACTR TRACTR + 3D CAB RF DEFLECTR TRACTR + FLAT BED TRAILER D TI TRACTR + BX TRAILER DI TI TRACTR + 3D DEFLECTR, BX TRAILER MAXIMUM PRACTICAL STREAMLINING, BX TRAILER D31 D I.917.i132 T TI EXTREME STREAMLINING, BX TRAILER D T Reference areas (Mdel Scale): DAF 33,.1437m2; T45,.15m 2 i

15 ~ I '~ r~ c u'~,--i,-4 ~ ~'~!!! c~ c~ ~ ~ ~--I c~ c~ c; ~ ~ u'~ '~! I S I I 9 ~ i= r~ ~ ~.-I c; ~,-I ~ ~ e~ ~J!! I I! I ~ ~ ~ ~ Z! ~ ~ ~J t~ t~ c s I '~ ~ ~ I I I I r-i =.f-i I.--I Z ~ ~ r,3 %%.~,-4 ~ ~ ~ C,-~,~ < F~ [zj "~ U~.l-.J 1-.), n~.~,.~.l,) Z (n ~1 ~ ~ ~.,~ ~--~ ~ ~ ~j ~ ~.,~ ~-J,-~ ~.~ ~ ~ ~ ~ c~ gc,-4 '~ f 3 i-i Z ~ ~J ' +~ + + q~ ~=~.,-~..,~., b, m t:~u) ~ ~ ~ ~ ~ Z Z,= ~ Z =,--4 H.~ ~-~ ~,-1,,-1 e,--1 m,,-1 " H m H ~ H ~ ~ ~.,~ r~ ~ ~ r~ ~ ~ ~ ~ ~ ~

16 f the varius aerdynamic devices used. T simplify the analysis and presentatin, discussin here is cncentrated n wind averaged drag measurements (CD~); a mre detailed appraisal is given by Cwperthwaite (i), sectins 2 t 4. Despite the different drags f the tractrs, the drags f the tw tractr-bx trailer cmbinatins are similar. Indeed, the T45 tractr, which has the lwer drag in islatin, leads t a slightly higher ttal drag when used with an unstreamlined bx trailer. The wind-average drags f the baseline tractr-bx trailer cmbinatins are higher than thse f the tractrs alne by 45% fr the DAF 33 and 11% fr the Leyland T45. The variatin f CDA with yaw angle fr bth baseline vehicles and bth tractrs in islatin is shwn in figure 7. This clearly illustrates the aerdynamic features f the vehicle discussed in the previus sectin; the bluff cab f the DAF shields the cntainer at lw yaw angles, resulting in a lwer verall drag, while the mre streamlined T45 expses mre f the cntainer frebdy t the freestream at zer yaw, increasing its drag. The bjective, in terms f reducing CDw A is t: (i) reduce the zer yaw drag (usually equal t CD~i, symmetric vehicle) and (2) reduce the rate f increase in drag with yaw angle 9. fr a This cncept is highlighted by the C D vs ~ data in figure 7 fr the "gd mdern practice" cnfiguratins, D34 and TII, fr which the tractr is fitted with a 3-dimensinal cab-rf deflectr and shrt tractr skirts and the trailer with a central gap seal and shrt trailer skirts. Fr these cnfiguratins CDA is seen t be virtually the same fr bth vehicles, particularly at lw yaw angles. f" 12

17 3.2.1 Summary f the effectiveness f varius devices - DAF 33 with a bx trailer (a) Cab rf deflectrs [Figure 8] - the 3D deflectrs appear t be mre effective than the flat plate type, mainly because their drag des nt rise as rapidly with yaw angle. (b) Tractr skirts [Figure 9] - there appears t be sme interactin between varius types f tractr skirt, i.e. frnt wheel cvers in islatin give a change in the wind averaged drag cefficient 6CD~ f -3% while the additin f frnt wheel cvers t lng tractr skirts des nt change the wind averaged drag. (c) Trailer sklrts [Figure 1] - n apparent benefit arises frm cvering the trailer wheels. therwise, prgressively increasing the degree f skirts gives a crrespnding reductin in CD~ (d) Tractr-Trailer gaps seals [Figure 11] - the effectiveness f varius gap seals was tested n a vehicle already fitted with ttal skirts, a base seal and tractr chassis fairing (cnfiguratin D15). The side and central (55%) gaps seals gave similar 6CD~A f -17% and -16% respectively. Increasing the size f the central gap seal t 9% further reduced the 6CD~A t -19%. A hrizntal gap seal had very little influence n this vehicle cnfiguratin, presumably because the tractr chassis fairing has a similar influence n the tractr-trailer flw field. (e) Cntainer frebdy devices [Figure 12] - the effectiveness f tw cntainer frebdy fairings was tested n cnfiguratin D15. The ttal frebdy mulding prved mre efficient than the cmmercial 'Windcheater' device, reducing the 6CDwAA t -17% cmpared t -13% with 'Windcheater' This is assumed t be due t (i) the increased leading edge radius ffered by the ttal frebdy mulding and (ii) the susceptibility f the Windcheater design t the type f tractr-trailer gap flw field. 13

18 3.2.2 Summary f the effectiveness f varius devices - Leyland T45 with a bx trailer (a) Trailer skirts [Figure I] - a prgressive increase in 6CD~A is btained as the extent f the skirts is increased, giving -9% 6CD~A fr full trailer and ttal tractr skirts. (b) Cntainer frebdy devices [Figure 13] - the effectiveness f tw cntainer frebdy fairings was tested n the baseline T45 vehicle. The ttal frebdy mulding (-17%, 6CDwAA) gave significantly better drag reductin than the cmmercial 'Windcheater' design (-9%, 6CDw~A ). (c) Cab rf deflectrs [Figure 14] - significant differences in effectiveness, the 3D deflectr giving a -19% 6CD~A and the plate deflectr -9%. 3.3 Discussin f the Aerdynamic Drag Measurements Results serve t cnfirm the well established bjective f matching the cab and cntainer flw field as being the mst effective way f reducing the drag f HGVs. The techniques fr crrecting a 'mis-matched' flw bviusly depend very much n the gemetry f the cab, but nevertheless cab rf 3D deflectrs appear t be the mst effective add-n device available. Hwever well matched the cab-cntainer flw, preventin f crss flw thrugh the cab-cntainer gap at yaw is pssibly the preferred next stage f mdificatin. A simple vertical gap seal is shwn t reduce drag in prprtin t the amunt f the gap it cvers. N significant differences between the effectiveness f side r central gap seals were detected. Tractr and trailer side skirts achieve similar bjectives t gap seals in preventing crss flw at simulated crsswind angles. They als serve t shield chassis prtuberances frm the free stream flw, althugh their true effectiveness in this respect may nt be apparent frm the wind tunnel tests, as they were cnducted 14

19 with statinary wheels. This may well explain the relatively small gains that were measured fr skirts that were extended t cver the tractr and trailer wheels. In terms f spray suppressin it is assumed that enclsing the wheels wuld cntribute significantly t the effectiveness f skirts, but cnfirmatin f this will require full scale trials. 4. SURFACE PRESSURE MEASUREMENTS 4.1 Wind Tunnel Measurements Surface static pressure measurements were made n the expsed faces f the bx cntainer at the lcatins given in figure 3, fr three mdel cnfiguratins:- (i) baseline (2) baseline + 3D deflectr (3) baseline + 3D deflectr + full trailer skirts. Measurements were made at yaw angles, 5, i, 15 and 2 degrees in the 8ft x 6ft wind tunnel and a cmprehensive set f isbar plts is given in Cwperthwaite (6). A definitin f the aerdynamic surface static pressure cefficient (Cp) n which the isbar plts are based, is given in Appendix B Cntainer frebdy and base The variatin f frebdy pressure distributin with yaw angle fr bth vehicles is given in figures 15 and 16. By integrating these pressure distributins we btain a drag frce due slely t the cntainer frebdy which can be expressed as a 'cmpnent' CDA in the same way as the drag frce n the cmplete vehicle. This technique clearly illustrates the cntributin f the cntainer frebdy drag t the verall drag, and the results given in table 4 emphasize the signlficance f tractr-trailer 'matching':- 15

20 Table 4: BASELINE VEHICLE YAW ANGLE Degrees 5 I 15 2 DAF 33 CNTAINER FREBDY Frebdy CDA (m 2 ) Percentage f Ttal ii LEYLAND T45 CNTAINER,FREBDY Frebdy Percentage CDA (m 2 ) f Ttal The use f cab rf munted 3D deflectrs changes the cntainer frebdy pressure distributins significantly, as shwn in figure 17. Very little change was seen in the cntainer base pressures. Cnsideratin f the crrespnding cntainer frebdy CDA values with a 3D deflectr, given in table 5, shw the significant reductins in drag that can be achieved. 6CDA is the difference between the frebdy CDA with and withut the cab-rf deflectr. Hwever, a cmparisn f the CDA/CDA~~(%) values and the verall CDA(% ) values taken by Cwperthwaite (i), (given in brackets in the table belw), suggest that the drag f the deflectr itself is significant at yaw, thus reducing the verall effectiveness. Careful ptimisatin f the shape f the deflectr thrughut the yaw range wuld therefre imprve the efficiency f this type f device still further. 16

21 Table 5: BASELINE VEHICLE WITH 3D DEFLECTR YAW ANGLE Degrees 5 i 15 2 DAF 33 CNTAINER FREBDY Frebdy with deflectr CDA (m ~) 6C~A (m 2) C~A/C,A~=(%) [11] 2 [1] 18 [8] 15 [7] 16 [6] 5 I 15 2 LEYLAND T45 CNTAINER FREBDY [3] [15] [6] [3] [-i] NB Figures in [ ] refer t the C~A/C~A~~= values measured during the frce/mment wind tunnel measurements, Cwperthwaite ( i). 6CDA is The additin f full trailer skirts did nt appear t change the cntainer frebdy pressure distributin f either vehicle, as wuld be expected. Hwever, small increases in base pressure were apparent, particularly ver the lwer area f the base, at yaw angles 5 and 1 degrees. This suggests that the skirts may be reducing drag nt nly by shielding the prtuberances arund the chassis and wheels, but als by mdifying the wake frmatin regin. 17

22 4.1.2 Cntainer sides The pressures n the sides f the cntainer r bx bdy were measured at yaw angles f, 5, i, 15 and 2 fr the baseline vehicles, the vehicles with 3-dimensinal cab-rf deflectrs, and with the 3-D deflectrs and full trailer skirts. The pressure differences increase with increasing yaw angle, with the largest pressure cefficients (see Appendix B) ccurring at angles f 15 r 2. The pressure differences n the windward side f the cntainer tend t be psitive (abve atmspheric) while thse n the leeward r dwn wind side are negative. Figures 18 and 19 shw the pressure distributins n the windward and leeward sides f the bx trailer at 2 yaw angle. The largest pressures ccur near the frnt f the cntainer, psitive n the windward side and negative n the leeward. Alng the rear 2/3 f the cntainer sides the pressures are relatively small and nly change slwly. Pressure cefficients near the frnt f the cntainer are typically ±.5, implying a pressure difference n the cntainer side f abut 19 Newtns/m 2 at 9 km/h. Fitting a 3-dimensinal cab rf deflectr and full trailer skirts increases the maximum pressure differences, particularly with the Leyland T45 tractr. n this vehicle cmbinatin the maximum pressure difference increases abut 5%, with the maximum pressure difference near the tp frnt crner f the side f the cntainer. 4.2 Full Scale Measurements Surface static pressure measurements were made n the full size bx cntainer, using bth tractr vehicles, n the TRRL research track and n a straight length f public rad. The pressure measuring system, essentially the same system as used in the wind tunnel experiments, is shwn in figure 5. bviusly, it is nt practical t cnduct full scale tests at a specified crsswind angle and therefre an attempt was made t cnduct all 18

23 the full scale measurements in nil-wind cnditins. Emphasis thrughut the full scale prgramme was n the validatin and repeatability f the test technique, in preference t maximising the number f different vehicle cnfiguratins tested. Cnsequently cmparisn here is restricted t that f the cntainer frebdy and base fr the baseline vehicle cnfiguratins. Further details f the full scale prgramme are given in Cwperthwaite (6) Cntainer rear bulkhead pressures Differences in pressure n the rear bulkhead f the cntainer were very small fr the three test speeds at which measurements were taken, 64, 8 and 96 km/h, and repeatability was acceptable. Cmparisn between the full scale and mdel bulkhead pressure distributins is difficult, because the unsteady nature f the flw means there is n established 'pattern' t the pressure cnturs. In spite f this, it is pssible t see that the surface pressure falls marginally frm the tp f the bulkhead t the bttm f the bulkhead in bth cases. Hwever, the magnitude f the bulkhead pressure cefficient is very different between mdel and full scale. Typical mdel bulkhead Cp's fr the T45 vehicle at zer yaw were, -.I t -.16 while the crrespnding full scale values were -.1 t -.8. In terms f ttal drag, this difference means that the wind tunnel measurements are ver-estimating the cntributin f the rear bulkhead drag, which has been shwn by Cwperthwaite (I) t be apprximately 9% f the ttal vehicle drag Cntainer frebdy pressure There were n significant changes in frebdy pressure cefficients fr either vehicle at the three test speeds f 64, 8 and 96 km/h, and repeatability f measurement, particularly at the higher speeds is seen t be gd. 19

24 Agreement between the full scale and mdel measurements depends n the vehicle cnfiguratin; crrelatin fr the Leyland T45 is gd, see Figure 2. The frebdy stagnatin regin is well defined and nly minr differences in magnitude f the pressure peaks are apparent. Hwever, the DAF 33 shws significant differences between tunnel and full scale, see Figure 21. Mdel measurements suggest that the separated flw regin abve the rf f the DAF cab deflects the freestream flw ver the cntainer frebdy, effectively shielding it frm the high pressure flw. Full scale measurements shw a large regin f near stagnatin pressure n the cntainer frebdy, similar t that seen n the T45 vehicle. 4.3 Discussin f Full Scale/Mdel Pressure Measurements A cmprehensive assessment f the pressure differences between full scale and mdel tests is given in Cwperthwaite (6).. Discussin here is limited t pssible reasns fr the significantly different flw field bserved n the DAF 33. The shape and extent f the separated flw regin abve the cab rf can be assumed t be dependant n: (i) the psitin f flw separatin n the cab rf (2) the freestream Reynlds number and turbulence intensity (3) the pressure/flw regime in the gap between cab and (4) cntainer the relative wind directin. The relative wind directin is seen frm figure 16 t prgressively increase the cntainer frebdy pressure as the effective yaw angle increases. The flw field depicted by the 5 degrees yaw case in figure 16 begins t resemble the full scale pressure distributin given in Figure 21. It is pssible therefre that ambient winds may have cntributed t the differences seen in the full scale tests. 2

25 Variatins in freestream turbulence intensity between the wind tunnel and full scale will influence the shape f the separated flw regin abve the cab rf, see fr example Bearman (7). Similarly, changes in freestream Reynlds number have been shwn by the authr (2, chapters 5 and 7), t influence cntainer frebdy pressure distributins, particularly at near ptimum cab-cntainer shielding. This may well explain why a similar effect was nt seen in the case f the T45 vehicle fr which the cab and cntainer flw fields are nt matched. A reasn fr the dependence f a near ptimum cab-cntainer flw field t Reynlds number is given in reference (2) as the influence f the Reynlds number n flw changes in the cab-cntainer gap at chassis level. Clearly, withut mving grund wind tunnel tests, the flw under the vehicle may well be different t that at full scale. Whilst it is nrmally assumed that the typical grund clearances fr HGVs are such as t reduce the significance f grund effect simulatin, it may well be that fr the finely balanced flw between cab and cntainer at ptimum interference, even such small differences are significant. The differences in pressure distributin between mdel and full scale n the DAF 33 may be imprtant t the aerdynamic ptimisatin f many future vehicles. The data made available by this research prgramme is nt sufficient t islate the cause f these differences and the prblem f crrelatin between full scale and wind tunnel simulatin techniques is seen t warrant further investigatin. 5. BUFFETING AND SPRAY DISPERSAL 5.1 Spray Dispersal A preliminary series f flw visualisatin studies were carried ut in the 8 ft (2.34 m) x 4 ft (1.2 m) bundary layer wind tunnel. The primary aim f these tests was t assess the effectiveness f using paraffin smke t simulate the dispersin 21

26 f fine water spray in the wake f the vehicle prir t full scale smke and spray trials. Smke was injected at ~ the vehicle's wheel arch. Using suitable illuminatin its subsequent dispersin was phtgraphed at varius statins dwnstream f the vehicle base. During the trials it was fund t be difficult t quantify changes in the wake prfile due t relatively majr changes t the vehicle cnfiguratin. Nevertheless, frm bservatin f the smke flw it was pssible t btain a gd subjective impressin f the areas arund and behind the vehicle affected by spray. It was quite clear that fr the better streamlined vehicles, particularly thse fitted with 3 dimensinal cab-rf deflectrs and extensive skirts, the smke simulating spray did nt spread as far sideways away frm the vehicle r s high abve the rad surface. technique Since the studies f the bx trailers were cmpleted the was develped by passing a thin vertical plane f light acrss the tunnel. The smke pattern at that plane can be phtgraphed t define accurately the simulated spray pattern at any plane alng the vehicle due t spray frm any individual axle (8). Use f smke t simulate spray culd be inaccurate because f aspects f the tunnel tests that cause the airflw near the grund and arund the wheel arches t be unrepresentative f full scale cnditins. These aspects are:- (a) the lw Reynlds number at which the tests were carried ut. (b) the relatively simple simulatin f grund prximity using a fixed grund plane (wind tunnel flr in this case). (c) the use f statinary, rather than rtating wheels. 22

27 Despite these limitatins, smke injectin was cnsidered t be a useful technique prviding its limitatins are recgnised. Mst imprtantly, smke des nt simulate the water splash generated by the tyres, the dispersin f which may well be significantly different due t the inertial frces invlved. Hwever, crrelatin with full scale smke and spray trials n the TRRL test track suggests that smke injectin warrants further develpment as a preliminary assessment technique. 5.2 Buffet assessment studies A similar preliminary exercise t that f the flw visualisatin was carried ut t quantify the degree f buffet that can be anticipated in the vicinity f the vehicle fr varius vehicle cnfiguratins. A series f measurements was made using pitt-static rakes at lcatins between the rear tractr wheels and the cntainer base. The aim was t map the lcal velcity prfile at each lcatin and attempt t quantify the subsequent buffeting that wuld be experienced by ther rad users, such as cyclists, light vans r car twing caravans. Hwever, as was anticipated, the flw field in this regin is very time dependent. This, tgether with the large lateral and reverse flw cmpnents, necessitates the use f mre sphisticated measuring techniques that were cnsidered beynd the scpe f the present study. The static pressure distributins alng the sides f the bx trailer give sme indicatin f the pressures t which a passing vehicle might be expsed, as well as the pressures that a curtainsided vehicle needs t withstand. The largest static pressures ccur when the vehicle is expsed t a crss-wind, and it is clear that the mre streamlined cnfiguratins generate larger pressure differences alng the sides f the bx trailer. 23

28 6. CNCLUSINS i. Wind tunnel tests n i/8th scale mdels f DAF33 and Leyland T45 tractrs twing a standard articulated trailer have shwn that significant reductins in wind averaged drag can be achieved using suitable cmbinatins f simple add-n devices. 2. The wind averaged drag f a vehicle CDw A with streamlining t gd mdern practice standards (3-dimensinal cab-rf fairing, shrt tractr skirts, partial trailer skirts and a vertical gap seal between tractr and trailer) was reduced, relative t the baseline vehicle, by 31% fr the T45 and 23% fr the DAF The drag reducing effectiveness f tractr and trailer side skirts - the devices recgnised as being mst likely t reduce water spray dispersin - is seen t be unaffected by tractr gemetry. This suggests side skirts are an effective additin t any vehicle f this class irrespective f individual design r layut. 4. The reductin f wind averaged drag prvided by varius cmbinatins f side skirt varied in prprtin with the extent f cver, reaching a maximum reductin f CDwAA (at 6 mph) f 12% fr the cmpletely skirted vehicle. 5. Running the tractr n its wn with a 3-dimensinal cab-rf deflectr increased the drag f the T45 by 33% but reduced that f the DAF 33 by abut 5%. This latter result may well apply nly t the tunnel mdel and nt ccur at full scale due t the lw Reynlds number (scale factr) f the tunnel tests. 6. Measurements f cntainer frebdy pressure suggest that whilst cab rf munted 3D deflectrs are effective in reducing drag, the drag f the deflectr itself can be cnsiderable at yaw angles greater than i degrees. Whilst the statistical weighting f drag at these relatively high crsswind angles is lw, this nevertheless des reduce the verall efficiency f the device and careful ptimisatin is essential. 7. Cmparisn between full scale and mdel surface pressure measurements shwed better crrelatin fr the Leyland T45 than fr 24

29 the DAF 33 tractr. This may be due t the susceptibility f the 'near matched' cab-cntainer flw n the DAF t external influences such as; turbulence level, freestream flw directin, grund simulatin and Reynlds number. These differences are such as t warrant further investigatin. 8. Pressure differences n the side f the bx trailer were measured with bth tractrs and with varius streamlining attachments. The largest pressure differences ccurred at yaw angles f The pressure differences increased as the streamlining f the vehicle was imprved. 9. Smke was injected int the wheel arches t simulate spray. While it was nt pssible t quantify the resultant flw patterns (a technique t analyse the flw patterns has subsequently been develped), it was pssible t btain a gd subjective impressin f the areas arund and behind the vehicle affected by spray. This technlque deserves further refinement and applicatin. i. The smke, simulating spray, did nt spread s far sideways r s high abve the rad fr the better streamlined cnfiguratins, particularly thse fitted with 3 dimensinal cabrf deflectrs and extensive skirts. 25

30 REFERENCES. Cwperthwaite, N.A. Scale mdel wind tunnel measurements n the Leyland T45 and DAF 33 vehicles used fr the TRRL spray dispersin prgramme. Cllege f Aernautics, Cranfield Reprt 8622, ctber Garry, K.P. Wind tunnel techniques fr reducing cmmercial vehicle aerdynamic drag. Cllege f Aernautics, Cranfield Reprt 822, September Ingram, K.C. The wind averaged drag cefficient applied t heavy gds vehicles. TRRL Supplementary Reprt 392, SAE Wind Tunnel test prcedure SAE J.1252, August fr trucks and buses.. Gilhaus, A. The influence f cab shape n the air drag f trucks. Jn Wind Eng and Ind Aer, 1981, 9.. Cwperthwaite, N.A. Full scale and wind tunnel mdel surface pressure measurements n the TRRL spray dispersin prgramme vehicles. CA Cranfield Reprt 8623,

31 . Bearman, P.W. Sme effects f freestream turbulence and the presence f the grund n the flw arund bluff bdies. Aerdynamic drag mechanisms f bluff bdies and rad vehicles. Plenum Press, Garry, K.P. A summary f the scale mdel wind tunnel tests n the TRRL spray dispersin articulated tanker vehicle. Cllege f Aernautics, Cranfield Reprt 896, May

32 lamb ~d i i 2.8 m. Figure 1. I z. L I ~ 2.9~:K) m. Leyland T45 Radtrain baseline vehicle. I

33 3. m. I t~ 3,m. Figure 2. DAF 33 baseline vehicle.

34 Upper surface 12 Side Frebdy Frebdy Upper surface 12ins /-, ins 12-.:':';I ;...,,!,,!!!,,!,,.,!. -, [, ~ ". ;,-12ins Q Q e r Q 6 Q i i G Q Q Q Q 4 Q -6 L - L _ Q Q Q Q Q Q i Q Q i 12 Q Q Q = g i ' I i i i I ~ I ' w I " " ' I i i I Side L 12ins 6ins Figure 3 Bx cntainer surface pressure tapping lcatins

35 Pressure Tapped Cntainer Scanivalve R Pressure Transducer Furncss FC4.1 mm H2 Scanivalve Cntrller Cmputer Interface C.IL. 63 Micrcmputer Cmmdre 332 Srs. Data Strage System. Figure 4 Schematic layut f the wind tunnel and data recrding system pressure measuring

36 Pressure Tapped Cntainer Scanivalv Pressure Transducer Furness FC4 1 / 25 mm H2 I Static Pressure Reference Pre-set Scanivalve Cntrl unit Frequency Mdulating Circuit Pressure Transducer Furness FC4 1 mm H2 Ttal Pressure ( Kiel Tube ) Magnetic Tape Recrder (a).n-bard data recrding system. Magnetic Tape Recrder ~_~ Frequency Demdulating Circuit v Analgue t Digital Cnverter Micrcmputer Cmmdre 332 Series (b). data transfer / prcessing system. Figure 5 Schematic layut f the full scale data recrding system. pressure m~asuring and

37 t-, m t~ u~ t- U5 t~. w ~_~ t- u~ J (..3 F-- ~ _~ a~3 r~ t~ ~D ~D v-- I m C J m I.. t; c I c. t- t;. m > U~ C~ ~~D - <] > t~ -.7 <D C~ C') C'3 C3 Z -.T c~ C 11 Q >- I,I.J > t; C~4 t~ c

38 . u~ g_,,1' -J > ~ ~ 8 ' R c~ "It) p. ~1,,'-.% "6 ~g

39 Flat plate deflectr (D 2) Curved plate deflectr (D3) 3 D deflectr, C f A design ( D 3) I I I -4-8.I 3D deflectr ~ Cmmercial design (D31) I I l ' ' %&CwA A Figure 8. Effectveness f varus tractr rf munted devces-baf33 Frnt wheel, cver ( D 5 ) Shrt tractr skirts ( D 8) Lng tractr skirts(d6) I a II -4-8 e/e A CDWA A TtaL tractr skirts (D7) Figure 9. Effectiveness f varius tractr skirts-.daf33

40 LEYLAND T45 Partial trailer skirts (D12) Full trailer skirts (D9)~(T12) Partial trailer plus shrt tractr skirts (D 13) Full trailer plus tng tractr skirts ( DI )~(T 13) Full trailer plus ttal tractr skirts (D11)~(T14) Base seat (D4) ~ -12 " -16 / AC DWA A Figure 1. Cmparisn f the effectiveness f vrius trller skirts the DAF 33 end LeylGnd T/-,5 vehicles. n

41 t I I, l Ttal skirts ~ base seal and tractr chassis fairing (D15) Cnfig. (D15) plus side gap seats (55%) (D16) Cnfig. (D 15) plus central gap seat (9%) (D 18) Cnfig. (D15) plus central gap seat (55%) (D19) Cnfig. (D15) plus hrizntal gap seat (D 17) I I I I i I I I % &C DWA A F=gure 11. Effectiveness f varius tractr-trailer gap seals-daf33

42 Cnfig. D 15 plus ttal frebdy mulding (D 22) Ttal skirts p bse seat and tractr chassis fairing (D15) Cnfig. D15 plus Windcheater" ( D 23) Cnfig. D15 plus ttal frebdy mulding and battai (D 24) I I I I I I I i I I I I -24 Cnfig. D15 plus ttal frebdy mulding central gap seat (73%) and curved plate, w deflectr (D27) -28 % ACDwAA Figure 12. Effectiveness f cntainer frebdy devices- DAF33

43 ! I i i Frnt under- run bar ' Windch ter'(t18) Tta[ frebdy mutding (T2) L I I -4 Figure 13. Effectiveness Battit (T21) I I! I i,, I I I I I I / A C DWA A f cntainer frebdy devices- Leyind T45. i DAF 33 Curved plate deflectr (D 3) LEYLAND T45 Curved prate deflectr (T17) DAF 33 3D deflectr, Cmmerciat design (D 31) LEYLAND T45,! I -4 I l I I & * I %Z~Cw A A 3D deflectr 9 Cmmerial design (T4) Figure 14. Cmprisn f and Leylnd trctr rf munted devices T45 vehicles. n the DAF33

44 /> + - ~ r ~ - A ~ ~ - ~. ~ "~ c :3 " m ~ c u..c ~'~ ~ ~ t~ ~ "~ ~'~ ~ 5 ~,. 8' v i i

45 U~ U ~, ~,~ ~ ~, e. ~ ~, ~.~_._. C "13 c.~ ~ ~'~ L,-- ~ :,~ I:~ " U -._..Q ~ ~ ~ "~-'~..,~.,,,...a ~.~--' ~ u~,~ _, ~ g/,'~b p~\''- '-,. \~ e~b e, i j i! ii~~~.,,._ I ( \_"\\\~"~"~-"~-".'..V/" "

46 LI_ - ~ "1 l-.af-~ ~_~N~ a- t:~._

47 J / / Ul._ > c /,\ J ~--~;..:.~ C ~ n.i.311 u C \ / /' / F Ul l-- v Ul L_ :3 4, I-- u (D (v) (vl LL >, Ul C~ i.. C~ "I N t..,g I,.. r~ c "I Ul e,1 4. (- t- "1:3 c._c 8 Ul.,4" I-- \ r~ Z --I >- i,i --I ~ t4-" ~~ ~w v ~. -e 81

48 ~...~,~ ~.,.4- a~g J L s / ~' - "5 r- ~ ~T, " C3..C3 ---,...---~.a.,~ 1 ~ ~ '~ _.,,,--~ ~ "8 " / li-.~ /! t I z ~ - '<C (/) ~..,.-- ~n :'N "E ' i i.,.~"'~

49 . ~-~---'~'--,..f - ~, \ Q 'gi:. i, i j ~ ;./,,' ;;.~! \,. ('~ ".. ~ ~.~ (l~'~.",/1,/ /!/,,.,,_,,... _ /~" /// /I - ",, "-~.~-e.6e _ ~ ' " / / I \ Wind tunnel mdel, zer yaw e see "Q-~.-;-.: ~.Gee... - ~C"~--~;-- i. ~ _L--_~:.-; 'b I Figure 2 Full scale vehicle, 6 m.p.h. Cmparisn f mdel and full scale surface pressure cgff. distributin, Lcyland T45 cntainer frebdy.

50 _-T~ ~_. "i" ~ - -, _ ~ \,' ~ ~. 2~ ; Wind tunnel mdel,zer yaw ' e e ~.se / Full scale vehicle. 4 mp~. Figure 21 Cmparisn f mdel and full scale surface distributin, DAF 33 cntainer frebdy. pressure ceff.

51 APPENDIX A The Wind Averaged Drag Cefficient In rder t make realistic calculatins f the effect f aerdynamic drag n a vehicle's fuel cnsumptin, it is necessary t take int accunt the effect f crsswinds. Insight int these cnditins can be achieved in the wind tunnel by measuring the aerdynamic frces n the vehicle at an angle f yaw t the freestream. Hwever, the true effect f crsswinds n a Vehicle's pwer utput is dependent n tw factrs:- (i) the frward velcity f the vehicle. (2) the wind velcity (at the vehicle height), and its directin relative t the line f travel. Bth these factrs are taken int accunt in the evaluatin f a wind averaged drag cefficient (C~), see Ingram (3). - VT V = lcal wind velcity VT = vehicle speed V~ = relative speed Frm the wind vectr diagram abve we can btain expressins fr the relative Wind speed (V~)and ~elative wind angle (B) in terms f the; wind velcity (V), vehicle speed (V.) and the wind directin relative t the directin f travel (~). This enables the definitin f a wind averaged drag cefficient as

52 // 27~ V... C.(8) [ 1 + (V/V.) ~ + 2(V/V.)cs~ ] p(v,~).d~.dv where C.(B) = bdy axis drag cefficient, btained fr each yaw angle by wind tunnel tests. p(v,~) = prbability f a wind speed V blwing at an angle relative t the freestream. It can be seen that evaluatin f wind averaged drag, at a specified vehicle cruising speed (in this case 6 mph) depends n the statistical predictin f wind speed (V) and directin ~. This predictin is made frm wind data at 19 meterlgical statins in the UK fr the years Each set f data is weighted accrding t the vehicle ppulatin density in its particular area, and the directin f nearby mtrways. Cnsequently the prbability functin p(v,~) can be usedand a wind averaged drag evaluated fr a particular vehicle, at a specified cruising speed n a UK mtrway. In practical terms, wind averaged drag cefficients are a statistical guide t the likely effect f changes in aerdynamic drag. Experience suggests that between 1/3 and 1/2 f the percentage change in C~ can be translated int a change in fuel ecnmy. This bviusly depends n numerus ther factrs, fr example vehicle all up weight, gearing, driving cycles etc.

53 APPENDIX B Definitin f Surface Pressure Cefficient (Cp) Measurements f surface static pressure n bth the mdel and full size bx cntainer are expressed in the frm f a pressure cefficient (Cp), defined as fllws:- Cp = p - p ½ /~ V 2 where p = pressure (N/m 2 ) P = freestream static pressure (N/m 2) = air density (kg/m 3) = 1.2 kg/m 3 at sea level V = velcity (m/s) The theretical maximum value f Cp is 1.. This crrespnds t a 'stagnatin' pint in the flw, ie a pint at which the freestream flw is brught t rest by the bdy.

54 < L~ -,,.% i [.~ < c~ L) un -.1"..T -.T ~';,-4,-4,,-~,-~ c; -.,-4 '.m u'% -.T,-s,,-4 L) i r) v <,-1 L),-4 '4 e"~ Cq C,4,'-4 r,-,i,--4,-"4,-"4 c~ E~ L,/ Z ~n m: < > ~,~,--1 < c~ L~ a. r~ c,4 (~3..?,-.4,.-4,--I,--i ~-I ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~"4 C ~-a' C~ ~"~ C~ L) L).-,4 % I '~ U3 C'M U~ (~ ~D r-.i ~ % ~ P~ P~ ~ ~D Q ~ ~ I I + I I I I I I P'I I I I I I I I I L) ~ ~ ~ ~ ~ ~ ~ ~ ~ m ~ ~ ~ ~ ~ ~ ~"~,.,.4 c.4,-,~ ~ ~ ~ ~ ~ ~ ~ ~ -,,~ P'- (a (a 4J,u (4,.~,. " ~J m m 1 4J,-4 4J ~J ~ 4-I ~ 4J,-4 4J,-4,-4 (~ ~I ~I.,-~..4 ~ ~ ~ v ~ m 4J 4~ 4J 4J,-4 4J,-4 m ~ 4J,-4 = ~ m m ~.el m m ~ m ~ ~ ~. ~ m ~ ~.~ ~ P~ Z %),--4,-4 = ~ = ~ = ~ G.. ~. ~. ~. ~. ~ ~ ~ ~ m m ~ ~ m

55 m~ < ::3: a CD ' ~ J,~ r~ ~ c cm u~ ~J c.d ~ lij u~ a C.D t.d c c~ u~ ce~ '~ r u'~,~,~ -.I" ~ ~- c~ C~ C u'~ u'~ I"'- r--,--~,~,--i,--~ ~--~ ~ ~,-~,,--4 C'~ C~ (,q I--I!,-,<. C.D " t,d C',I r-,...~- ',..~- c,~,--~ c..i,-4 c.~....~" u-~ c~..1" u-~,.--~ c C,~ C~l c~l c..,i,--,l,,--i.,..j- C~l c,~ c,c,,--~.... c~c; c; c; i C~ c~ r-< t.d '-",-I ~ i -4- i,i,i c.~,,.t",i.~..~" i t i I i i! J i ~) < ~ c ~ C~ r',- r-i,,-i ~,-~,--i C~ ~'~1 ~ ~ ~ ". u'~ ", ~ ~-. C ~ r'-- ',. C c ",.. t'-.- ce~ ~ C~ C~ C~ '~ "~ '~ C~,--I,-~,-~ c; c; c; p-. ~ ~D C~,--I,-,I,I c'~ C,,I c~ -.,T u'~ ",. r--- c ",,--~ c,,i r'~,'~,"-, ~:~ ~:~ C:~ ", ", "-~ "~,"~ c3 cr~ ej ' C C~,--4 u~ a w,-4 vc~,-.-i ~ Cu u-~,~ ~,u, "~ -,--~ v,--~ ' ' n3 m,--~ U,'~ ~.-~ D ~ C~ J c~,.~ ~..~ ~ ~:~,.c ~,.~ C~.,~ :>~ ~ :>~.~ c,'~ ~ ".,~ qj ~ qj CL (J " ".~ (j ~ (j ~ u) I-i m ~ " r~ ~ ~ ~ ~-~.~ 2~ I--I u'~ u'~ u"~,.-t ~--I r--i ~ ~ ~ ~ Q; C ~ Q; ~ + + v u3 u3 u3 u~ U3 u~ + + C.9 I-I,-.I.,-I.,..I,~.,~.,~.,~.,~.,.~ ~ ~,-~,-~ ~D ~D ~D ~D ~,-~ ~ ~ u] ~

56 q I l i l i i, i i. t-i c; ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ C,I i I ~ ~ C'~ ~ ~ ~ c~ r-4 q C.J. i i i i i l i i ".u ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~D [-~ ~x,-4.z: 1-4 '-'! i "5",-~ ~J 4 cm -4 ~.,I cq r.. rj r~!!,i c e~ u~ Ch ~ ~ cq 'i ~ q..~.,.4 r,~ ('~ 4J,. ~,~ ~C,~ ~ "~,~,-~ ~J ~ (J ~ ~-~ " ~',~.~,~ ~ ~ ~ ~ (~ q~,~3 "~3 ~ ~ ~.,~.,~ ~J ~ C,-~,~ " " ~ [-, " ~D - (D u~ c~ u~ in ~..4 Q; r~,.-4 ~ D ~ D ~ ~ ~ u~ ~ ~ ~..~ ~D,-4 I'--I r.~ LU + ),,-I,--I ) u~ &J ~ ~ ~ ~ ~ ~ :3 ~ ~ ~ ~ ~ ~ ~ ~ ; J ; ; C C C ~ C.-4.~.-4.4.~ i.--i,-4.-~ ~-~.-4 ~; Q; ) Q) ; ~ Q ~Q,. r,,~ ~ m m c~ m ".-4,..C qb v f-..,.q

57 +, Descriptin f Aerdynamic Dcvuccs= lnsg k tractr :irts fuu trailer skirts shrt tractr skirts. partiq! trailer skirts cab frnt wheel skirt shrt trailer skirts base sgcti ttal tractr skirts are lng tractr skirts, cab frnt wheel skirts

58 height (h),.61 m width (w),1.'/2 m ( deflectr can be curved r fiat) cab rf munted plate deflectr J under run bar cab rf munted 3D deflectr central gap seal (side gap seal similar n s,des f bx bdy ) battail hr=znta[ gap s4zal

59 cntainer frebdy mulding I Windcheater I' ', tractr chassis fairing (see phtgraph w~rleaf ) '\ / 2-43 m / \.J -- 2"43 m cntainer frebdy mulding 2R.125W / T B 1 "5H 1 R W - Windcheater

60 Tractr chassis fairing (DAF 33 tractr unit)