The Characteristics Of Car Exhaust Drag Reduction And Exhaust Diffusion Of The Collaborative Optimization Research

In recent years, problems of energy crisis and the air pollution by exhaust diffusion have getting more and more prominent as the result of the growing car ownership. Improving the vehicle fuel economy and controling the exhaust diffusion have becoming the hotspots and frontiers in current car manufactures researches.Effective solutions to these problems are inseparable from the car aerodynamics.Therefore, the research on the aerodynamic characteristics of cars to reduce aerodynamic drag and the law of automobile exhaust diffusion control is of great practical significance.Currently, the optimization for aerodynamic drag characteristics is primarily achieved through streamlined body design and improvement of local modeling and other methods. Limited by the styling, crafting and cost, these methods can be hardly improved to reduce the aerodynamic drag. So we must find a new way to reduce drag and further improve car’s aerodynamic characteristics. Studies have shown that the wake vortex is the main characteristics causing aerodynamic drag, and exhaust emissions of the vehicle during driving has an effect on the wake vortex. Moreover,exhaust emissions is determined by the structure of the exhaust pipe, at the same time,the sharp increase in emissions and less diffusion of the exhaust during high idle speed will significantly pollute the air quality on the pedestrian’s breathing zone,which is also closely related to the exhaust pipe design. Therefore, it investigated the influence of the exhaust pipe design on the characteristics of the aerodynamic drag and the exhaust diffusion is of great practical significance, but they are of complex coupling relationship, meanwhile, Multidisciplinary Design Optimization through fully using the synergistic effect between different objects, to gain an overall satisfaction solution, which has been rapidly developed and widely used in the aerospace field. However, collaborative optimization has just begun in the field of automotive design. As a result, considering the coupling relationship between the exhaust drag reduction and exhaust diffusion can avoid the one-sidedness disadvantage which only takes single performance into account,therefore,it has very important theoretical and practical significance.Firstly,this paper attached importance to numerical simulation, then combined with the wind tunnel experiment,the characteristics of the exhaust drag reduction andexhaust diffusion of a micro-bus was studied from the perspective of car aerodynamic feature.At last, based on the above research, a exhaust pipe structure with low resistance, low pollution was designed by means of collaborative optimization method.The main research contents are as follows:1. Based on experiment data, in consideration of the computational accuracy and efficiency via simulation, comparative analysis of the different turbulence models and mesh strategies’ adaptation on the numerical simulation of tail gas was carried out,from which the optimal turbulence model and mesh strategy were chosen and finally simulation scheme applied on exhaust emission was determined.2. To begin with,the trailing vortex drag reduction for the exhaust emission was put forward, and its feasibility is verified afterwards. Then the change rule of exhaust drag reduction at different speeds, different shapes, different positions and different angles is obtained by CFD simulation, based on this rule, drag reduction method is put forward on account of pulsating exhaust emissions. Finally, the drag reduction mechanism of tail gas constant emission and pulsating emission is comparatively analyzed in detail by transient calculations.3. At first,the pedestrians’ breathing zone is confirmed,and then the effect of exhaust diffusion properties at different speeds, different shapes, different positions,different angles on pedestrians’ breathing zone are investigated by using component transfusion model. At last,the corresponding law is obtained.4. Considering the characteristics of the exhaust drag reduction and exhaust diffusion, a innovative tail pipe emissions was proposed, whose parameters were optimized by using the collaborative optimization method. At the same time, in order to improve the optimization efficiency, based on the integrated technology that combined computational fluid dynamics and optimization algorithm, the exhaust pipe structure which can reduce the tail gas drag as well as the exhaust diffusion that had an effect on the pedestrians’ breathing zone was obtained.