Optimization Design of Rear-Engine Bus Cooling System Based on 1D/3D Coupling Simulation 2018-01-0771

This study investigated the effects of underhood structure parameters (two types of air ducts, two types of inlet grilles and the opening angle of inlet grilles) on the cooling characteristics of the rear-engine bus; then, the optimum design scheme of the underhood was determined. The air-side resistance load of the cooling system, which is based on fan performance, was selected as the optimization objective. Simulations were created based on a porous media model and standard a k-ε model. The next step was to build a 1D/3D coupling simulation to utilize the advantages of 1D simulation’s fast convergence speed and 3D simulation’s extensive research range. Besides, the use of 1D/3D coupling simulation can efficiently avoid the errors of simulation results which arise from the non-uniform airflow on the cooling module. Results show that the airflow rate of the rectangular air duct increased by 7 to 11percent. Compared with the airflow rate of the underhood without an air duct, the air resistance load of an underhood with a rectangular air duct was less than that of an underhood without an air duct. The airflow rate of the vertical bar-shaped grille was higher than that of the horizontal bar-shaped grille, and it was highest at the 45°opening angle. According to the results, the air duct and grille were chosen as the critical design variables. The optimal design scheme of the underhood was obtained by investigating the combined effects of air ducts and inlet grilles on the cooling performance of the engine. When the underhood structure consists of the rectangular air duct and the 45°opening-angle of the vertical bar-shaped grille, the air flow rate attains its maximum state. In addition, the cooling air resistance load becomes lower; the lowering speed of air resistance gets quicker as the vehicle speed accelerates, and it tends to be steady at 90 km/h. The new scheme is effective at improving the cooling capacity.