Study On The Aerodynamic Characteristics Of Two Cars Moving Side By Side

The aerodynamic characteristics is one of the most important parameters for road vehicles (especially the passenger cars), which has a great effect on the performance, fuel economy and handling quality. And the main factor of affecting these performances is the flow characteristics around the vehicle, which determines the forces and moments in the six degrees of freedom. Now the number of road vehicles increases greatly, so it's difficult to avoid the driving situations, such as the convoy of cars, overtaking and cars moving in opposite crossing. High-speed vehicles encounter drastic gust loads when driven in close proximity to each other. Such phenomenon is identified as aerodynamic interference between road vehicles. The interference between road vehicles imposes additional forces particularly side forces and yawing moments on vehicles. According to the driving situations, aerodynamic interference is classified: 1. Vehicles moving in one lane 2. Vehicles moving in the same direction in two neighboring lanes 3. Vehicles moving in opposite crossing Continuous developments in automobile industry have lead to both faster and lighter vehicles. Lighter vehicles are necessary for vehicle's manufactures to fulfill the requirements of both fuel economy and raw material conservation. In particular such lighter vehicles are susceptible to a severe drift when overtaking (or when overtaken by) a larger vehicle, which can contribute to the performance and passengers'safety. Two cars moving side by side in the neighboring lanes is a transient state of overtaking process. In real driving situations, it takes few moments for the two cars to be side by side. However, this type of interference has a considerable effect on the car's stability and passengers. This is the subject of my paper exactly, and at the same time the study is a part of the project of the Natural Science Fund (GM Creation Fund), which will fill up the blank of this field in china. This paper makes the numerical simulation of exterior flow for a single car and two cars moving side by side using the international standard MIRA model (1:1). The shape of MIRA model is simple, and it is always used to do comparative tests. At present the numerical simulation of a single car has been done well, but the numerical simulation of more than one car is in the initial state and the wind tunnel tests about the aspects are still very few in China. We can compare the results of a single car and two cars moving side by side based on the results of a single car, and then identify the turbulent characteristics and the laws of aerodynamic interference. So the numerical simulation for two parallel cars is a comparative test to some extent, and MIRA model is suitable for the study. The two models are placed in the center of every road according to the width and the boundary condition adopted is the moving ground during the process of numerical simulation. At the same time because of the simple geometrical shape, this paper uses the hexahedron mesh to ensure the computational precision. The computational model is k ?ε/high Reynolds Number turbulence model. Although it has many shortcomings, it is used widely because of higher solution ability, shorter computational time and lower requirement for the mesh quality. This paper analyzes the flow characteristics of a single car and two parallel cars moving in neighboring lanes, and then compares the distribution of velocity and pressure and the wake structure of two cars with a car's. From figures we can see that the distribution of velocity and pressure around the vehicle is not only asymmetrical but different from a single car's. Simultaneously lower pressure zone appears in the inner side of two cars which imposes additional side forces to each car. Additionally the wake structure has changed. The wake behind each car is biased towards the outer surface of the car (they are asymmetrical), and a pair...