


                 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 CD-Adapco

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.



                                 Attachment 1



                                     Case
                                  Description
                                      -9
                                      -6
                                      -3
                                       0
                                       3
                                       6
                                       9
                                      101
                                   Baseline
                                     0.580
                                     0.503
                                     0.452
                                     0.422
                                     0.453
                                     0.514
                                     0.589
                                      102
                                  No Fairings
                                     0.630
                                     0.540
                                     0.472
                                     0.439
                                     0.478
                                     0.558
                                     0.644
                                      103
                                 Bell Fairing
                                     0.622
                                     0.534
                                     0.472
                                     0.438
                                     0.475
                                     0.551
                                     0.632
                                      104
                               Underbody Fairing
                                     0.588
                                     0.509
                                     0.454
                                     0.424
                                     0.460
                                     0.523
                                     0.598

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 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 differences are in the flow field.

 
 

 
      
