Validation Studies for an Advanced Aerodynamic Development Process of Cab-Over Type Heavy Trucks

The implementation of an advanced process for the aerodynamic development of cab-over type heavy trucks at China FAW Group Corporation (FAW) requires a rigorous validation of the tools employed in this process. The final objective of the aerodynamic optimization of a heavy truck is the reduction of the fuel consumption. The aerodynamic drag of a heavy truck contributes up to 50% of the overall resistance and thus fuel consumption. An accurate prediction of the aerodynamic drag under real world driving conditions is therefore very important.

Tools used for the aerodynamic development of heavy trucks include Computational Fluid Dynamics (CFD), wind tunnels and track and road testing methods. CFD and wind tunnels are of particular importance in the early phase development. While wind tunnels provide a physical test environment with repeatable conditions their availability is very limited and they also have several other limitations which make it difficult to predict on road performance of the truck. Such limitations are blockage and pressure gradient effects, lack of road simulation and Reynolds number effects. While on the other hand CFD does not have such limitations the accuracy of CFD is often questioned and needs to be proven. In this study an extensive test program for a FAW heavy truck has been carried out in the wind tunnel of the National Research Council Canada (NRC). For a direct comparison of forces and pressures between wind tunnel and CFD, a model of the wind tunnel is included in the CFD simulations and a blockage correction method consistent with the NRC wind tunnel correction is applied to the CFD results. CFD is also used to predict the drag under open road driving conditions and results are compared to the blockage corrected data from wind tunnel test and simulation. For further correlation, measured and simulated results for wind averaged drag are then entered into a fuel consumption model to predict the fuel consumption for open road cruising at 90 km/h which is compared to respective test track measurements.