Research On Aerodynamic Characteristics Of Vehicles Driven Out From Tunnel Under Consistent Crosswind

With the increase of road mileage and the rapid growth of car numbers year by year, our country is entering the automobile age rapidly. As we all know, our country’s terrain is very complex and most of the area is mountainous. Mountains and hills account for more than two thirds of the total area. To ensure the rationality and continuity of the road, more and more tunnels will used to get through mountains. In addition, more and more highway tunnel and submarine tunnel appeared with the expansion of city. When a vehicle out from a tunnel, the aerodynamic characteristics of the vehicle will rapidly change because the space of the vehicle is from closed to open. China is a windy country, the roll force of the vehicle will rapidly increase because the crosswind, thus causing traffic accident like out of control and side tumbling. Moreover, many vehicles will running side by side and in platoon in the road, this will change the flow field around the vehicle and affect the security of driving.A mesh updating method is put forward which is based on dynamic layering technique in this paper. Studied the aerodynamic characteristics of vehicles out from road tunnel under crosswind, analyzed the causation between the flow phenomenon and the results of mechanical. Conclusions are as follows:Firstly, studied the aerodynamic characteristics of a van out from road tunnel under crosswind by transient numerical simulation method. Comparative analyzed the data result with the date of steady numerical simulation method. The error is under the allowable so it can provide a basis for further study.Set four pairs of running speed and every running speed corresponding four pairs of wind speed to study the aerodynamic characteristics of a van out from road tunnel under crosswind. The aerodynamic drag coefficient of the van decreased when out from the tunnel, the drag coefficient and lateral force coefficient will increase when the wind speed increase. The aerodynamic characteristics of the van seriously fluctuates near the tunnel’s exit, and fluctuates became more obvious when the wind speed increased. The flow field around the van become more complex and effect the safety of driving.Set the running speed is 30 m/s and four pairs of wind speed to study the aerodynamic characteristics of two queuing vehicles out from road tunnel under crosswind. Used the standard car model and change the position of the car and the van to comparative analysis. The drag coefficient of the two vehicle will be decrease when two vehicles trail each other, and the drag coefficient of the latter vehicle will decreased more when the frontal vehicle is larger. The aerodynamic characteristics of the latter vehicle will be fluctuates because of the trailing vortex of the frontal vehicle. The effect of the trailing vortex to the latter vehicle was less when the frontal vehicle is relatively smaller and the latter vehicle is relatively bigger.Set the running speed is 30 m/s and four pairs of wind speed to study the aerodynamic characteristics of two of two vehicles side by side out from road tunnel under crosswind, and change the position of the car and the van to comparative analysis. The drag coefficient change trend is similar when two vans side by side out from road tunnel. The lateral force coefficient of the two vans is similar but the direction of the lateral force is opposite without crosswind. The lateral force coefficient of the left van on leeward side is less than the right van on windward side under wind condition, and the ratio of tangential force coefficient and drag coefficient of the right van is less than 1. The phenomenon shows that the right van can shielding crosswind to some extent. The drag coefficient change trend is similar when a car on right and a van on left side by side out from road tunnel. The lateral force coefficient of the two vehicle is similar but the direction of the lateral force is opposite without crosswind. The lateral force coefficient of the two vehicle will increase when the wind speed increased, but the increasing extent of the van on left becomes smaller. The ratio of tangential force coefficient and drag coefficient of the left van is more than 1. The phenomenon shows that the right car can shielding crosswind to some extent, but the effect is small because the frontal area of the car is small. The ratio of tangential force coefficient and drag coefficient of the left car is less than 1 when a van on right and a car on left side by side out from road tunnel because the frontal area of the van on windward side is relatively large. The aerodynamic characteristics of the car seriously fluctuates because the van on windward can side shielding crosswind.This paper studied the aerodynamic characteristics of vehicles out from road tunnel under crosswind. Proposed possible reasons why traffic accidents generally occurred near the tunnel’s exit from the aspect of aerodynamic. The results of this paper provide evidence for the safe driving under the crosswind.