Experimental Study And Numerical Simulation Of The Aerodynamics Performance And Drag Reduction Measures For The Bus-like Body

With the development of the highway and the price of the fuel oil being higher, the aerodynamics performance of commercial vehicles has attracted more and more attention. This paper which aims at one bus-like model has researched the law of the aerodynamics characteristics affected by the configuration parameters with the method of wind tunnel tests and numerical simulation; Based on pressure distribution and the external flow field character of the model, an effective drag reduction measures is raised, and that will provide important reference for the vehicles similar to this model; At the same time, both the velocity distribution and the aerodynamic characteristics of different bottom simulation as well as different ground clearance are discussed preliminarily, which will be used as a reference for the similar models.This paper includes five chapters, and the major contents are as follows:The first chapter is an introduction, which mainly depicted the background and the significance of the research. Combined with the time requirment of China's automobile industry development, the progress of research domestic and abroad such as commercial vehicle configuration, flow field of the bottom and the drag reduction measures have been investigated in detail, and also the main research contents in this paper are epurated. In this paper, based on the Ahmed model, the interrelated research work is carried out via wind tunnel tests and numerical simulation.The research foundation of numerical simulation on vehicles is shown in chaper two, including control equations for external flow field, common discrete methods, commercial CFD software and pre-processing software. In the numerical computation, the model is accomplished with the CAD software SolidWorks, and it is imported into ICEM-CFD to generate unstructured grid. Then both the aerodynamics loads and the post-processing are obtained via FLUENT software.At last, the reliability for the selected grid strategy and the turbulence model is verified with an example.In the third chapter, both tests in the 1.4m×1.4m low speed wind tunnel in CARDC-L and the results of the typical configuration parameters′aerodynamics performance are introduced. In the tests, the boundary layer measurement on the floor, typical configuration parameters effect, different ground clearance of different models bottom state effect, the flow field measurement test of the bottom, drag reduction and flow pattern visualization test are all carried out. In addition, the aerodynamic characteristics effect on the typical configuration parameters(such as head transition radius, tail declination angle, underbody diffuser angle, tail transverse contraction angle)is analyzed, the results show that with the head transition radius increasing, the drag coefficient is reduced and the lift coefficient is increased, while the radius increases to a certain value, the change will be slowed down;When the tail configuration angle is properly changed, both the drag coefficient and the lift coefficient are reduced, but beyond a certain angle, different results will be shown for various changes. Meanwhile, the rear surface flow pattern of two different angles is visualized with the method of oil flow and gridding tufts.The research on the drag reduction measures and the flow field of the bottom is introduced in the fourth chapter. Accordding to the features of external flow field and pressure distribution of the model, the clapboards fixed on the rear for drag reduction is proposed. The results show that the arrangement of the clapboards is determined by wake structure, the impact of drag reduction is affected by the width of the clapboard and the distance far from the trailing edge of the model, and the drag coefficient in present study is reduced by 15.58% when the clapboard arranged as three clapboards in both horizontal and vertical directions. As for the research on the flow field of the bottom, the boundary layer thickness of the floor is measured at first, and the test results agree with the theoretical datas well. Based on this, the ground clearance is given to simulate ground effect with the method of fixed floor. And then, using the pressure measurement rake, a preliminary study is carried out on the flow field of different ground clearance in different bottom states, which also gives the velocity distribution along the longitudinal center line of the bottom and the laws of the flow field development. Otherwise, the aerodynamic characteristics of different ground clearance in different bottom states is analyzed.It is a summary of the thesis in the last chapter, which also presents the shortage in this paper and the direction on the future work.