# Optimal Design of an Ecofriendly Pickup Truck Overhang and Roof to Reduce the Drag Coefficient
###### Abstract  
Until now, various studies have been conducted on the drag coefficient of pickup trucks, but little research has been conducted on the effect of the front overhang length and roof design on the drag coefficient. In this study, the flow characteristics and drag coefficients of 54 models with different front overhang lengths, roof angles, and angular positions were compared using a computational fluid dynamics code to reduce the drag coefficient of an eco-friendly pickup truck. Reducing the aerodynamic drag of electric vehicles can improve battery utilization and improve the overall performance of the powertrain, so it is important to analyze and optimize geometric design steps to improve drag reduction strategies. The three-dimensional steady-state analysis model used in this study was verified by comparing the model results with experimental values reported in previous studies. In addition, the impacts of four factors on the drag coefficient were analyzed to develop an optimal design that takes into account smaller and better characteristics. The drag coefficient was reduced by 10.3% compared to that of the base model. Based on the numerical analysis of all models to be applied to pickup truck design, a correlation of the drag coefficient with the shape was proposed, showing a low error range of +1.9% to \(-\)1.74%. p 2024 2024 2024 2024 2024 2024 2024 2024 2024  
fuel economy by increasing the power consumption of the vehicle, indicating the need for aerodynamic performance improvement [3]. Various studies have been conducted to reduce the power consumption of pickup trucks. The analysis of the flow field of a pickup truck is difficult because of the open bed behind the cabin. Therefore, [PERSON] et al. [4] presented the experimental data of the flow near the wake of a pickup truck. They reported a recirculating flow region on the bed but none on the top of the tailgate. [PERSON] [5] compared the drag coefficients of six shapes of pickup trucks through experiments and computational fluid dynamics (CFD). It was found that the drag coefficient was the lowest for the sedan-type truck and highest for the SUV-type truck. Owing to the square-shaped accessories of the bed, the drag coefficient of the SUV-type truck was twice as high as that of the sedan-type truck. The open bed behind the cabin of a pickup truck makes the flow field more complex than that of conventional vehicles. This is because the wake zone changes depending on the bed geometry. Previous studies found that the bed geometry, such as the length and height of the open bed, affects the drag coefficient and confirmed that the height of the bed is a dominant factor for the size of the wake zone [6; 7]. Unlike an open bed, a closed bed allows the streamline to fall smoothly behind the vehicle. In this case, the size of the wake zone decreases, making it possible to obtain a lower drag coefficient than in the case of the open bed. Flaps are devices used to reduce drag. [PERSON] et al. [8] added two types of flaps with various angles at the four corners of the 25\({}^{\circ}\) and 35\({}^{\circ}\) slopes of the standard Ahmed model, thereby reducing the drag by up to 21.2% through changes in the wake. [PERSON] et al. [9] researched the optimal angles and lengths of the rectangular, elliptical, and triangular flaps in bluff body models similar to square-back road vehicles such as trucks and buses, rather than the streamlined form. The maximum drag reduction rate of 11% was observed when the elliptical flap had an angle of 50\({}^{\circ}\). [PERSON] et al. [10] attached a flap near the rear edge of the cabin roof such that the bed flow could be directed toward the tailgate. The drag coefficient decreased as the downward angle and length of the flap increased, even though the backflow increased in the wake zone. However, when the downward angle exceeded a certain value, the drag coefficient tended to increase. Therefore, it is important to determine the optimal flap conditions.