A Two-Dimensional External Aerodynamics Tool (EAT) for Simulating Airflow around Tractor-Trailer Combinations

Understanding external vehicle aerodynamics is an integral step in reducing overall vehicle fuel consumption. This is particularly true for long-haul commercial vehicles where an incremental decrease in drag can translate into significant fuel savings based on the number of miles traveled over the course of a truck's working life. The ability to critically analyze the air motion adjacent to commercial vehicles is a step toward understanding the overall affects of external aerodynamics on the entire vehicle. To achieve this understanding, the aerodynamics problem must be divided into manageable tasks that can each yield qualitative and quantitative results.

A two-dimensional (2D) External Aerodynamics Tool (EAT) has been developed that enables computational fluid dynamics (CFD) simulations of commercial vehicles to be performed quickly and easily. The approach is significantly automated and uses tools of ICEM CFD Engineering and FLUENT™ as well as a highly customized user interface to produce fully quadrilateral grids and CFD solutions from the original CATIA™ CAD data. The simulations are based on centerline cross-sections of entire tractor-trailer combinations. Although the complete vehicle is included in the simulation, the CFD results are meant to guide the design of grill bars, sun-visors and profiles of hoods, windshields and roofs. EAT is intended to enable designers to make informed design decisions based on aerodynamic performance while taking into account styling considerations. This leads to shorter design cycles and minimizes prototype costs through reducing the necessary number of design variations to be tested through more in-depth methods such as three-dimensional CFD analysis or wind tunnel testing. A validation of EAT has been performed through a series of simulations of an NACA 4415 airfoil as well as a sun-visor similar to the Freightliner Century Class production sun-visor. Finally, a brief description of the application of EAT within a sun-visor pre-optimization design study is presented.