AERODYNAMICSLABORATORY Improving the Aerodynamic Efficiency of Heavy Duty Vehicles: Wind Tunnel Test Results of Trailer-Based Drag-Reduction Technologies Unclassified Unlimited LTR-AL-2015-0272 July22,2015 BrianR.McAuliffe AERODYNAMICSLABORATORY Improving the Aerodynamic Efficiency of Heavy Duty Vehicles: Wind Tunnel Test Results of Trailer-Based Drag-Reduction Technologies ReportNo.: LTR-AL-2015-0272 Date: July22,2015 Authors: BrianR.McAuliffe Classification: Unclassified Distribution: Unlimited For: ecoTECHNOLOGYforVehicles StewardshipandSustainableTransportationPrograms TransportCanada Project#: A1-004876 Submittedby: Dr. StevenJ.Zan,DirectorR&DAerodynamics Approvedby: JerzyKomorowski,GeneralManager,AerospacePortfolio Pages: 95 CopyNo: Figures: 61 Tables: 14 ThisreportmaynotbepublishedwhollyorinpartwithoutthewrittenconsentoftheNationalResearch CouncilCanada LTR-AL-2015-0272 DragReductionforHDVs-WindTunnelTestResults Disclaimer This report reflects the views of the authors only and does not reflect the views or policies of Transport Canada. NeitherTransportCanada,noritsemployees,makesanywarranty,expressorimplied,orassumesany legal liability or responsibility for the accuracy or completeness of any information contained in this report, or process described herein, and assumes no responsibility for anyone’s use of the information. TransportCanadaisnotresponsibleforerrorsoromissionsinthisreportandmakesnorepresentations astotheaccuracyorcompletenessoftheinformation. Transport Canada does not endorse products or companies. Reference in this report to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by Transport Canada and shall not be used for advertising or service endorsement purposes. Trade or company names appear in this reportonlybecausetheyareessentialtotheobjectivesofthereport. ReferencesandhyperlinkstoexternalwebsitesdonotconstituteendorsementbyTransportCanadaof thelinkedwebsites,ortheinformation,productsorservicescontainedtherein. TransportCanadadoes notexerciseanyeditorialcontrolovertheinformationyoumayfindattheselocations. Classification: Unclassified NRC-CNRC v Distribution: Unlimited LTR-AL-2015-0272 DragReductionforHDVs-WindTunnelTestResults Executive Summary ThroughitsecoTECHNOLOGYforVehiclesprogram,TransportCanadacommissionedthe NationalResearchCouncilCanada(NRC)toinvestigatetheaerodynamicimprovementspos- sible with current and emerging drag reduction technologies for heavy-duty vehicles, with theintentofguidingfutureimplementationandregulationofsuchtechnologiesforCanada’s transportationindustry. Awind-tunneltestcampaignwasundertakenintheNRC9mWind Tunneltoevaluatetheaerodynamicperformanceofvariousdragreductionconcepts,withan emphasisonthosefortrailers,usinga30%scalemodelofmoderntractor-trailercombinations. ProjectstakeholdersalsoincludeEnvironmentCanada’sTransportationDivision. A wind-tunnel approach was taken for the project because of its ability to provide a precise measure of the aerodynamic differences between vehicle configurations. Advancements in testing techniques developed for the project have improved the accuracy of the results, such that they reflect better the aerodynamic performance of a tractor-trailer combination under real-world conditions. These advancements consisted of a modular model that can represent various tractor configurations (sleeper-cab and day-cab with various roof-fairings for each) and trailer configurations (40 ft dry-van, 53 ft dry-van, 53 ft half-height dry-van, 53 ft flatbed withvariouscargoconfigurations, tandem28ftlong-combinationvehiclearrangement). The model has spinning wheels matched to an appropriate ground-effect simulation consisting of a boundary-layer suction system and a moving ground plane. Cooling drag is simulated with an engine compartment through which the flow-rate is proportional to that of a real vehicle. The30%scaleofthemodelissmallenoughtominimizewall-interferenceeffectsinthe windtunnelevenwitha53ft-equivalenttrailer,yetisbigenoughtoprovidetheaerodynamic performanceofafull-scalevehiclethroughappropriateReynolds-numberscaling. Inaddition tothemodel,anewRoadTurbulenceSystem(RTS)hasbeenintroducedintheNRC9mWind Tunnelthatprovidesroad-representativeturbulenceinthewind. Alloftheseadvancescreate theappropriaterelativemotionsbetweenthevehicle,theground,andthewindsuchthatthis representsthemostadvancedwind-tunnel-simulationofaheavy-dutyvehicleintheworld. The overall test program described herein included distinct sub-studies to address drag re- duction techniques for various regions of the vehicle or for different vehicle types. For each vehicleconfigurationtested,thewind-tunneldrag-coefficientmeasurementswereusedtocal- culate a wind-averaged-drag-coefficient that represents a long-term average of the aerody- namicperformancefortypicalNorth-Americanwindconditions,fromwhichfuelsavingsand greenhouse-gasreductionshavebeenestimatedbasedontypicalCanadiandrivingdistances. The table on the next page summarizes the main findings of the study, with fuel savings and greenhouse-gasreductionestimatesforsomeoftheconfigurationstested. Classification: Unclassified NRC-CNRC vii Distribution: Unlimited LTR-AL-2015-0272 DragReductionforHDVs-WindTunnelTestResults Drag-ReductionTechnique FuelSaved† CO2Reduction† [l/tractor/year] [kg/tractor/year] Tractor-TrailerGap: reducetractor-trailergapby12" 800±200 2,100±500 addtrailerfairingforsleeper-cabw/36"gap 600±200 1,600±500 addtrailerfairingforday-cabw/36"gap 1,600±500 4,200±1,300 TrailerUnderbody: addside-skirtstotandemaxletrailer 2,900±800 7,700±2,100 addextendedside-skirtstotandemaxletrailer 3,300±900 8,700±2,400 addside-skirtstotridemaxletrailer 3,800±1,100 10,000±2,900 TrailerBase: addlongorshort4-panelboat-tailtotrailerbase 1,900±500 5,000±1,300 addtapered-side3-panelboat-tailtotrailerbase 1,600±500 4,200±1,300 TrailerUpper-Body: profilethetrailerroof(top6") 1,000±300 2,600±800 Combinations: 48"to36"gap,trailerfairing,side-skirts,boat-tail(sleeper) 6,700±1,900 17,700±5,000 48"to36"gap,trailerfairing,extendedskirts,boat-tail,profileroof(sleeper) 8,300±2,300 21,900±6,100 48"to36"gap,trailerfairing,side-skirts,boat-tail(day-cab) 7,900±2,200 20,900±5,800 48"to36"gap,trailerfairing,extendedside-skirts,boat-tail(day-cab) 8,600±2,400 22,700±6,300 FlatbedTrailers: addside-skirtstoflatbedwithhighirregularcargo 2,900±800 7,700±2,100 addside-skirtstoflatbedwithlowirregularcargo 1,600±400 4,200±1,100 LongCombinationVehicles-LCVs: addtrailerfairingtoLCVtrailer-trailergap 1,400±400 3,700±1,100 reduceLCVtrailer-trailergapfrom5ftto3ft 1,900±500 5,000±1,300 addtrailerfairingandreducegap,andaddfullaeropackagetoLCV 7,900±2,200 20,900±5,800 Tractor-TrailerHeightMatching: removefull-heightfairingfromday-cabwithlowdry-vantrailer 5,400±1,500 14,300±4,000 removefull-heightfairingfromday-cabwithfull-heightdry-vantrailer -5,400±1,500 -14,300±4,000 †estimatedfor125,000±35,000km/tractor/year@100km/hr Reducingtheaerodynamicdragassociatedwithdry-vantrailerswastheprimaryfocusofthe currenteffort,andseveralregionsofatractor-trailercombinationweretargetedwithdifferent drag reduction technologies. For these efforts, the vehicle model represented a modern aero tractor with a 53 ft dry-van trailer. The drag-reduction techniques tested do not represent specific commercial products, although some were designed to achieve drag reduction in a similarmannertotechnologiesonthemarket. Thegapbetweenthetractorandtrailerisaregioninwhichaircancirculateandpassthrough, and is a dominant source of drag for a tractor-trailer combination. Many modern tractors are outfitted with side-extenders that reduce the effective air-gap between the two bodies, and provide a reduction in fuel use, however operational restrictions may prevent the abil- ity to achieve such savings. To better understand the sensitivity of vehicle drag to the gap width,measurementswereperformedforseveralgapwidthsanditwasfoundthatthewind- averaged-drag was reduced by 2.6% for every foot the gap was reduced (8.5% per metre). A one foot reduction in gap width, which may be operationally feasible for many vehicles on viii NRC-CNRC Classification: Unclassified Distribution: Unlimited LTR-AL-2015-0272 DragReductionforHDVs-WindTunnelTestResults the road, translates to a reduction in fuel consumption on the order of 800 litres per tractor peryear,withCO emissionsreductionsof2,100kgpertractorperyear. Anactivefifth-wheel 2 system can provide such benefits at highway speed without adversely affecting low-speed manoeuveringandoperations. Anothertechniquetoreducedragassociatedwiththetractor- trailer gap is to introduce a device that prevents air from flowing through the gap region. Of theconceptstested,alargetrailerfairingwasfoundtoprovidethegreatestbenefit,withdrag reductions on the order of 2% for the sleeper-cab tractor variant tested, and 5% for the day- cabvariant,providingassociatedfuelsavingsof600litresand1,600litrespertractorperyear, respectively. Reducing the gap width and adding a trailer fairing can provide fuel savings in excess of 2,000 litres per tractor per year and greenhouse-gas reductions in excess of 4,000 kg CO pertractorperyear. 2 AswouldbeexpectedbasedontheirprevalentuseonNorth-Americanhighways,side-skirts provide the greatest drag reductions of the trailer-underbody concepts tested. By redirecting the wind around the trailer, they prevent high-momentum air from being entrained in the underbodyregionandfromimpingingonthetrailerbogie. Dragreductionsof10%weremea- suredfordifferentside-skirtarrangementswithatandem-axletrailerbogie,andextendingthe skirtsoverthetrailerwheelsprovidedanaddedbenefitsuchthatfuelsavingsexceeding3,000 litres per tractor per year may be realized. An even greater reduction in drag was measured for side-skirts applied to a tridem-axle bogie arrangement, with fuel savings of nearly 4,000 litrespertractorperyearandgreenhouse-gasreductionsof10,000kgCO pertractorperyear. 2 RecentfederalregulatoryamendmentsinCanadahaveopenedupthepossibilityofapplying aerodynamic fairings, commonly called boat-tails, to the aft end of dry-van trailers that are larger than previous regulations allowed. Several boat-tail concepts were tested to examine theinfluenceofalowerpanel,thesensitivitytolength,andtherelativepotentialforinflatable boat-tails. All showed similar results, with the greatest benefit realized from the four-panel configurations (6-7% drag reduction), providing an estimated fuel savings of 1,900 litres per tractor per year and greenhouse-gas reductions of 5,000 kg CO per tractor per year. The 2 short(2ftfull-scale)andlong(4ftfull-scale)boat-tailconceptsshowedthesamelevelofdrag reduction. Removingthelowerpanelandreducingthesurfaceareaofthesidepanelsshowed only a small reduction in performance (5-6% drag reduction), providing further evidence to support the hypothesis that the manner in which the top panel guides the air downwards towards the ground is the dominant influence on boat-tail performance. Other studies have shownboat-tailstobeaseffectiveasside-skirts,reachingdragreductionsof10%. Thevertical offsetofthetoppaneltestedhere(3inchesfull-scale),includedtoleaveroomforlightsatthe top edge of the trailer base, may be a reason why the boat-tail concepts tested here have not providedthesamemagnitudeofdragreductionsobservedforothersimilarboat-tailconcepts. Thispresentsaclearchallengetodevelopingeffectiveboat-tailsforreal-worldapplications. Theintentofthecurrentstudywastoevaluatewaysofreducingthedragassociatedwithdry- vantrailerswithoutchangingcargocapacity. Inanefforttomodifytheshapeoftheroofwhile minimizing any influence to the cargo volume, the top 6 inches of the trailer were modified in three ways: rounding the front edge, rounding the side edges, and tapering the aft edge. The aft taper provided the greatest benefit of the three, however the combined profiled roof provided a drag reduction of 3.5%, which translates to 1,000 litres per tractor per year in fuel savingsandareductioningreenhousegasemissionsof2,600kgCO . 2 Classification: Unclassified NRC-CNRC ix Distribution: Unlimited LTR-AL-2015-0272 DragReductionforHDVs-WindTunnelTestResults Ofthevarioustechnologiestested,somedidnotprovideanymeasurabledragreductionsand some showed increased drag. A partial plate seal applied to the front face of the trailer and paired to the sleeper-cab with a 36 inch tractor-trailer gap showed no significant reduction in wind-averaged drag. Removing the landing gear, smoothing the trailer underbody, and addinganunderbodydiffuserfairingallshowedasmallincreaseinwind-averageddrag. For these attempts, it was found that by reducing the resistance to flow in the underbody region, a greater flow-rate is introduced in this region which increases the drag of the trailer bogie. Roof mounted vortex generators also showed increased wind-averaged drag. These various poorly-performing concepts do not represent specific commercial products or concepts and the designs used have not been optimized. These test results should not be taken to mean such concepts will not work, only that they show much lower potential for fuel savings than thewell-performingtechnologiesandthattheymustbecarefullyoptimized. Thebestperformingtechniquesforeachregionofthedry-vantrailerwerecombinedtoexam- inetheadditivepropertiesofthevarioustechnologies,andsimilarcombinationswerepaired withboththeday-cabandsleeper-cabvariants. Significantdragreductionsofupto29%have beenobservedforsomecombinations. Fuelsavingsinexcessof8,000litrespertractorperyear are predicted for some combinations (greater than $10,000 per year at current diesel rates). Greaterreductionswereobservedfortheday-cabthanthesleeper-cabtractor,andhavebeen attributed to the sleeper-cab guiding the wind over the gap region in a smoother manner as a result of its length, thus receiving less gains from the gap devices. Of particular note, it was found that side-skirts and boat-tails have a mutually beneficial interaction that provides a reduction in drag from their combined use that is greater than the sum of their individual drag reductions. An additional 3% drag reduction was observed in the current study when the extended side-skirts and boat-tail were paired. This interaction has been identified as a possiblesourceofdiscrepancyforperformanceclaimsreportedinliteratureofside-skirtsand boat-tailswhentestedinacombinedmannerasopposedtowhentestedindividually. In addition to the full-height 53 ft single dry-van trailer, the current project examined other trailertypesincludinga53ftflatbedtrailerwithdifferentcargoconfigurations,atandem28ft dry-vantrailer,anda53fthalf-heightdry-vantrailer. Thiswasdoneinanattempttoidentify fuel savings measures for a greater proportion of tractor-trailer combinations found on the road. Different tractor roof configurations were also tested for some trailer configurations to examinethesensitivitytopropermatchingofthetractorwiththetrailer. Side-skirts were beneficial for all the flatbed configurations tested, but the magnitude of the drag reductions varied (5% to 8%). A mid-height tractor roof was shown to benefit all of the flatbedcargoconfigurations,evenforasetoflargeboxeswithamaximumheightthesameas afull-heightdry-vantrailer. For the tandem 28 ft trailer, which was used to represent a long combination vehicle (LCV), reducingthetrailer-trailergapfrom5ftto3ftwasmostbeneficial,butaddingatrailerfairing or full-plate seal in the trailer-trailer gap provided measurable drag reductions. The same magnitudes of drag reductions were not realized when the rest of the trailer regions were treatedwithside-skirts,aboat-tailatthebaseoftheafttrailer,andafairingonthefrontofthe forwardtrailer. A25%dragreductionwasmeasuredforthefullaerodynamictreatmentofthe LCVconfiguration. x NRC-CNRC Classification: Unclassified Distribution: Unlimited