Combined Analysis of Cooling Airflow and Aerodynamic Drag for a Class 8 Tractor Trailer Combination

Long haul tractor design in the future will be challenged by freight efficiency standards and emission legislations. Along with any improvements in aerodynamics, this will also require additional cooling capacity to handle the increased heat rejection from next generation engines, waste heat recovery and exhaust gas recirculation systems. Fan engagement will also have to be minimized under highway conditions to maximize fuel economy. These seemingly contradictory requirements will require design optimization via analysis techniques capable of predicting both the aerodynamic drag and engine cooling airflow accurately. This study builds on previous work [1] using a Lattice Boltzmann based computational method on a Volvo VNL tractor trailer combination. Simulation results are compared to tests conducted at National Research Council (NRC) Canada's wind tunnel. Correlation between simulation and experiment is presented for a half scale model, including the overall drag, surface pressure at locations over the truck outer surface and anemometer data collected behind the grille opening. Correlation for anemometer data is also presented for a full scale production truck in the same wind tunnel. The full scale production truck was then simulated in an on road environment to understand the impact of the wind tunnel environment on engine cooling airflow. Finally, the simulation results were analyzed to understand the limitation of using scale model tests to evaluate engine cooling airflow.