Evaluation and Optimization of Aerodynamic and Aero-Acoustic Performance of a Heavy Truck using Digital Simulation

The engineering process in the development of commercial vehicles is facing more and more stringent emission regulations while at the same time the market demands for better performance but with lower fuel consumption. The optimization of aerodynamic performance for reduced drag is a key element for achieving related performance targets. Closely related to aerodynamics are wind noise and cabin soiling and both of them are becoming more and more important as a quality criterion in many markets. This paper describes the aerodynamic and aero-acoustic performance evaluation of a Dongfeng heavy truck using digital simulation based on a LBM approach. It includes a study for improving drag within the design of a facelift of the truck. A soiling analysis is performed for each aerodynamic result by calculating the accumulation of particles emitted form the wheels on the cabin. One of the challenges in the development process of trucks is that different cabin types have to be designed. The aerodynamic performance study considers a high roof and a low roof version of the truck. For the high roof version, the existing model is compared to the initial facelift version. Design recommendations for guide vanes, sun visor, mirrors and roof fairing are derived from the flow analysis. The design changes are then applied by morphing the simulation model and tested by simulating the modified geometry in a very short design cycle. While drag is improved by 7.4% the detailed analysis shows that not all changes are really effective and that in particular soiling is affected in an adverse way. For the low roof version of the truck the effectiveness of a roof fairing is evaluated by comparing to the low roof model without roof fairing and to the best high roof model. The aero-acoustic evaluation considers two areas of interest. The first one is typical greenhouse wind noise where wall pressure fluctuations (WPF) on the glass panels are main contributors to the interior noise. Problem areas are identified through surface dB maps and design recommendations are derived from a detailed analysis of the flow structures. The second area considers problems that are related to appendages like a sun visor or the roof fairing. Such problems have occasionally been observed on trucks and a methodology to address such issues in the development process is shown.