The Aerodynamic Performance Optimization And Experiment Study Of Heavy-duty Truck

With the advent of oil price up and hazy weather and national five emission regulation implement recently, energy saving has become an essential requirement in automobile design. The drag coefficient has great impact on vehicle fuel economy. Attaching aerodynamic accessories to heavy-duty trucks to reduce drag coefficient using Computational Fluid Dynamic(CFD) simulation optimization and wind tunnel experiments has turned into an important method. Because heavy-duty trucks possess high cab, big frontal area, large aerodynamic drag and bad crosswind stability. There is a very urgent need to improve aerodynamic performance under crosswind to ensure fuel economy and running safety.The thesis focuses on anti-drag additional devices mounted at the heavy-duty truck to optimize its aerodynamic configuration. Some methods are used to reduce the drag coefficient of heavy-duty trucks under the side wind, such as attaching the proper transverse and longitudinal gap seals add-on devices between the cab and container, mounting side skirts at the lower part of the container and installing tail-board at the rear end of the container. CFD numerical simulations are executed to investigate aerodynamic performance of the heavy-duty truck under the effects of the crosswind with different yaw angles. The results show that aerodynamic forces and moments increase with a great rate as the raise of yaw angles. Crosswind has significant effects on traveling safety and handling stability. Aerodynamic reduction mechanism of transverse and longitudinal gap seals is investigated in this paper and velocity, pressure, vector and turbulence kinetic energy of the flow field around the heavy-duty truck under the effects of the crosswind with different intensity are also discussed. The analysis is performed of the phenomena that the aerodynamic force and moment change with different add-on devices using FLUENT software. Moreover, wind tunnel tests on the scale model of heavy-duty trucks are carried out to measure six-component forces and airflow distribution of the rear part of the vehicle using 3-D Particle Image Velocimetry(PIV) at different yaw angles. Analysis results indicate that by attaching the proper add-on devices, such as transverse and longitudinal gap seals,the front airflow separations of container reduce. One of the most remarkable things is that the side force and rolling moment dropped in slightly compared with the original vehicle, and fuel economy performance is remarkably improved without affecting its handing and stability performance. Finally, combined simulation and optimization are developed to tail-board and side skirt add-on devices to reduce the aerodynamic drag received by heavy-duty trucks. The side skirt can prevent air flow from side and the tail-board can delay the separation of airflow in the rear part, improving the flow characteristics of tail eddy and making the vortex core far away from the body. In this study, the drag coefficient and pressure of the heavy-duty truck cruising at 25m/s are analyzed by CFD simulation. After consideration of the baseline result of CFD, the length and angle of side skirt and tail-board are chosen as design variables for optimization. Moreover, a Support Vector Regression approximation model is constructed with 30 experimental points generated by the Optimal Latin Hypercube methodology. As a result, an aerodynamically optimized side skirt and tail-board for heavy-duty truck in which the aerodynamic performance improves by about 8.2%, when compared to the baseline vehicle.