A Study Of Aerodynamic Characteristics And Optimization On A 12-Meter Coach

The performance of power, fuel economy, security and stability of a coach is significantly determined by aerodynamic characteristics due to its high speed, large front area& passenger capacity and heavy mass when cruising in motorway. In order to improve the compressive performance as well as strengthen competitiveness of coach market, plus accelerate the development of energy-saving on public transport sector and advocate green travel and energy conservation &emission reduction slogans, it’s essential and meaningful to develop aerodynamics research of a coach.Both numerical simulation and experiment optimization methods are employed to carry out the aerodynamic characteristics analysis and optimization of a 12-meter coach. The main contents include:(1) The effect law between aerodynamic characteristics and partial parameters of coach is investigated. A simplified coach model is established. The validity of the numerical simulation program is verified based on Ahmed model and against with wind tunnel test data. The hybrid meshing strategy is employed and the meshing no-relation analysis is launched. The effect of partial parameters on aerodynamic drag and lift coefficient of a coach is assessed and demonstrated with pressure contour, velocity contour and turbulent kinetic energy contour. The outcomes indicate the drag coefficient decline while the lift coefficient increase as the parameters of the front top transient radius, front side transient radius, front spoiler angle and rear windscreen angle is goes up. Whereas with the back spoiler angle and diffusion angle rise, the lift coefficient goes down while the drag coefficient accelerate and plunge separately.(2) Optimization on partial parameters to decrease the resistant drag coefficient of a coach is developed. In order to get the combination of partial parameters of a coach with a minimum drag coefficient, the orthogonal design method is used to optimize the partial parameters by using the difference analysis and variance analysis method. The results showed that: the impact sequence for resistant drag of a coach is front side radius>front top radius>rear spoiler angle>front spoiler angle>rear windscreen angle>diffusion angle. The minimum aerodynamic coefficient of parameter combination is front top radius 1000 mm, front side radius 1000 mm, front spoiler angle of 8, rear spoiler angle-10, rear windshield angle 20, diffusion angle 6.(3) The design principle of rear view mirror is explored based on aerodynamic characteristics of a coach. A CAD model of a coach is established by previous aerodynamic characteristics analysis and optimization outcomes, plus taking sufficient consideration of space, aesthetics and styling and other factors. The external field of aerodynamic characteristics is analyzed. Afterwards, 4 different shape rear view mirrors are designed and the effect to aerodynamic drag coefficient of a coach is analyzed &assessed. The design principle of rear view mirror are proposed. The results showed that: rear view mirror body with a curved surface modelling, arc transition and symmetrical arrangement; the linkage between stent and bearing bracket & mirror body should have a smooth transition; the support have arc transition edge and reduce the lateral extension length, which can reduce aerodynamic drag coefficient of coach.The aerodynamic characteristics of a coach is developed including analysis of the effect between aerodynamic characteristics and partial parameters, the optimal partial parameters combination with minimum resistant drag coefficient and the overall design of rearview mirror as well. The research results can be applied to provide a reference for preliminary design and optimization of coach, which has a significant influence in reducing exhaust emission and improving fuel economy.