UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

Washington, DC 20460

OFFICE OF

AIR AND RADIATION

July 12, 2011

MEMORANDUM

SUBJECT: Summary of Computational Fluid Dynamic simulation results provided by CDAdapco

FROM: Arvon Mitcham, Mechanical Engineer, and Sam Waltzer, Environmental 

Engineer.

TO: Docket EPA-HQ-OAR-2010-0162

This memorandum provides for docket the technical information and data resulting from 

computational fluid dynamics (CFD) simulations to support the rulemaking Control of 

Greenhouse Gas Emissions from Medium- and Heavy-Duty Vehicles Notice of Proposed 

Rulemaking (EPA 420-F-10-038). These simulations were conducted using the geometry

provided by EPA created from the scan of a long-haul, sleeper cab tractor as well as a standard 

53 foot box trailer. The scanning of the tractor and trailer was conducted by Southwest Research 

Institute under EPA contract and is detailed in a separate report. The CD-Adapco simulations 

were run using their STAR CCM+ software and their best practices. The frontal area used in the 

calculation of a coefficient of drag is 10.7699. The attachment is summary of the results 

provided to EPA via email from Fred Ross, CD-Adapco.
Case Description -9

101 Baseline 0.580

102 No Fairings 0.630

103 Bell Fairing 0.622

104 Underbody 

Fairing 0.588

Baseline has both front fairing, and underbody fairings on. Case 102 removes both, 103 just has the 

fairings on the front, and 104 just below the trailer.

I did find some leakage into the front tires, since the hub of the tire was open. I just closed that, and 

added some refinement to the trim of the trailer. I don’t expect major trend changes, but it might shift 

the data slightly. The trailer landing gear is in the down position. I don’t see this as a major issue. The 

mud-flaps pretty much go to the ground, blocking

The Bell Fairing may not be having a large impact due to the CAB design, and possibly the open, or 

missing CAD between CAB and trailer. But I can certainly compare more images to see where the 

differences are in the flow field.

2

Attachment 1

9 -6 -3 0 3

0.580 0.503 0.452 0.422 0.453 0.514

0.630 0.540 0.472 0.439 0.478 0.558

0.622 0.534 0.472 0.438 0.475 0.551

0.588 0.509 0.454 0.424 0.460 0.523

both front fairing, and underbody fairings on. Case 102 removes both, 103 just has the 

fairings on the front, and 104 just below the trailer.

I did find some leakage into the front tires, since the hub of the tire was open. I just closed that, and 

some refinement to the trim of the trailer. I don’t expect major trend changes, but it might shift 

the data slightly. The trailer landing gear is in the down position. I don’t see this as a major issue. The 

flaps pretty much go to the ground, blocking the flow to the truck supports.

The Bell Fairing may not be having a large impact due to the CAB design, and possibly the open, or 

missing CAD between CAB and trailer. But I can certainly compare more images to see where the 

6 9

0.514 0.589

0.558 0.644

0.551 0.632

0.523 0.598

both front fairing, and underbody fairings on. Case 102 removes both, 103 just has the 

I did find some leakage into the front tires, since the hub of the tire was open. I just closed that, and 

some refinement to the trim of the trailer. I don’t expect major trend changes, but it might shift 

the data slightly. The trailer landing gear is in the down position. I don’t see this as a major issue. The 

The Bell Fairing may not be having a large impact due to the CAB design, and possibly the open, or 

missing CAD between CAB and trailer. But I can certainly compare more images to see where the 
3
4