Aerodynmaic Character Research On External Flow Field Of The Coach

With the continuous development of the bus industry and improvement of the manufacturing technology, the external shape and aerodynamic characteristics of the big coaches are drew attention more and more. the external flow field around the big vehicles which is closely related to the air resistance coefficient have the coach suffered force and torque, and have a direct impact on bus operating costs, so the Numerical simulation of the external flow field have a practical significance.This article connects with the design optimization of 12M coach which is the highlight project of our company and we adopted methods as theory analysis and numerical simulation in this text to carry out the analysis of the Drain Field Dynamics of the coach. During the study, take into account that there are some elements can impact the external flow field, and the different elements has different study level, if we select the comprehensive test method, need to use the 36=729 kinds of the analog computation. So this article selects orthogonal design to study the radii of front side pillar,forward degree,the radii of top pillar and backside Pillar,tilted tail and radii of the bottom Pillar, selected the orthogonal test form to fix the calculation program of this article, so greatly reduce the computational efforts.for assuring the exactly of the computing result, firstly, we tested the k-εmodel of Fluent. For the coach, in the normal speed, all the Reynolds number is in the scope of the High Reynolds number (>104), meanwhile, has the similarity with the cube, so this article selects the k-εmodel to calculate the resistance of cube disturbed flow, and compared with results of classic fluid theory, the difference is only 0.67%, this prove that this method has feasibility. The program of analog computation according to the Orthogonal test has been used the Fluent to calculate the simplified model of coach and made the range analysis to result using direct analysis. In the end we get the optimal combination of various factors. we analysed the influence on air resistance coefficient because of the various factors changes by using scatter curves and discussed relationships between the air-condition location and the aerodynamic drag. Finally considering the best combination of orthogonal test table, air-condition position and front bulge and other factors, to determine the optimal upgrade program, and made a simulation optimization computing.Research shows:⑴The most optimal combination is not in the part implemented experimentation by using the orthogonal test method, which indicates that the optimization results is not simply the part reflection of the information, but rather the comprehensive test information. The more optimum combination of experimental results directly from the orthogonal experiment is similar to the best program and the optimal scheme is also appropriate.⑵Changes in air-condition location has little influence on the drag coefficient.⑶The optimization of the radii of front side pillar,forward degree,the radii of top pillar greatly reduced the flow separation of the front part of the coach, and reduced energy loss and pressure on the front of vehicle area,which is the important measures to reduce the air resistance coefficient.⑷The optimization of the radii of backside Pillar,tilted tail and radii of the bottom Pillar weakened the flow separation in the of the back part of the coach and reduced the energy loss by whirlpool, at the same time the pressure of rear body may be raised, which is the other important measures to reduce the air resistance coefficient.⑸Front bulge can further reduce air resistance coefficient.In short, the study and conclusion of this article has the significance to decrease the Air resistance coefficient and the value to further optimization of product design.