The Bus Body Numerical Modeling Of The Flow Field Around The Space Discretization And Model Wind Tunnel Test Study

This dissertation is mainly discussed in the following three perspectives: the numerical modeling of bus body surface, the space discretization for numerical simulation of flow field around bus using finite element method (FEM) and wind tunnel test for bus model.The numerical modeling of bus body is the base for bus styling and space discretization of flow field around bus. With a one-fifth wooden bus model, an experiment is carried out to measure model surface data by a CMM. The "Method of Grids Identified In Advance" and the "Method of Probe Touching Point Coordinate Adjustment" are recommended in this experiment. The measurement of bus model shows that the two methods are simple and efficient. According to the theory of reverse engineering, an interface is worked out between coordinate data and UG ( Unigraphics? software, then the data are read into UG and a numerical model , which is suitable to describing bus body, is well set up from the powerful functions of free surface feature of UG software.The method of generating elements and nodes automatically by reading coordinate data on surface of bus body is introduced and realized to discrete the topology space of three-dimensional turbulent flow field around buses. In order to control the grids density, the "Method of Generating Elements Along Line Proportionally " is adopted. The "Method of Advancement Along the Least Node Amount Direction" can optimize the node code in the same element. A program for space discretization of flow field around bus is developed under the platform of Windows98. This program has achieved the main work of the FEM preprocess. It shows that the above two methods are feasible and highly efficient.In order to supply the comparative data for numerical simulation of flow field around bus, a wind tunnel test for this model was carried out with an aeronautic wind tunnel. The aerodynamic force and surface pressure data are measured completely, and flow visualization is also conducted in this wind tunnel test. The analysis of aerodynamic drag data shows that air drag coefficient reaches 0.539. The analysis ofchanging transitional corner between the front and top of the model illustrate that air drag coefficient can be reduced 23.30%. The surface pressure distribution can be a basis for choosing the inlet of engine cooling airflow and ventilation reasonably. The analysis of the repeated test data shows the maximum deviation of air drag coefficient is less than 0.88% and the deviation of the most surface pressure data is within 1%, it illustrates the test data is reliable.