Browse Publications Technical Papers 2019-01-0668

Numerical Analysis of Underbody Diffusers with Different Angles and Channels 2019-01-0668

The basic structure of large-scale commercial vehicles (such as bus) is roughly bluff body and will produce high aerodynamic drag and aerodynamic lift at high speed. Among them, the wake structure contributes more to aerodynamic drag, and the bottom pressure distribution contributes more to aerodynamic lift. The installation of diffuser at the bottom of the vehicle can increase the speed of the airflow passing through the bottom of the vehicle, thereby reducing the pressure on the bottom of the vehicle body. Then the downforce will be increased the vehicle stability wil be improved. The diffuser was first used in racing cars and later gradually applied to passenger cars. In this paper, the CFD simulation method is used to study the aerodynamic characteristics of the bus under different diffuser inlet and outlet angles, and then an optimal inlet and outlet angle is determined based on the simulation results. Then, using this angle as a constant, the 2, 3, and 4 channel numbers were chosen as the diffuser channel variables to study the influence of the multiple-channel diffusers on the aerodynamic drag of the vehicle. The results of the study show that reasonable diffuser inlet and outlet angles can improve the bottom pressure distribution and wake structure of the bus, resulting in a maximum increase in downforce of 38.2%. In addition, under a certain diffuser angle, different numbers of diffuser channels have different effects on the drag coefficient and the lift coefficient. However, due to the smooth bottom surface and large ground clearance, the effect is small.


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