Study On The Aerodynamic Drag Reduction Of A Truck

With the development of the highway in our country, highway transportation has become the fastest and most convenient way of the transportation systems. The velocity of the truck on the highway keeps increasing, even reaches 80-120km/h. Currently it's a tendency to increase the transportation efficiency by velocity. However the high speed brings with the increasing drag,and that makes the consumption on the drag power be the direct ratio to the cube of the speed. So decreasing the drag properly can save large a mount of energy, especially the drag of commercial vehicle such as heavy-duty truck and tractor-trailer truck. With the development of the economy, the tractor-trailer truck is widely used, however because of the requirement of cargo transportation, it is hard to decide the best aerodynamic figure, and that leads the bad aerodynamic characteristic and poor fuel economy. In our country, there are not many studies on the tractor-trailer truck; this paper is trying to do some basic research.The purpose of this paper is to reduce the drag of a truck made in our country and make it reach the best fuel economy. The 1:1 scale model is used in the paper, and the different aerodynamic attachments are mounted on the truck separately, for example the, the air shield and vanes,side safety panel,the splitter on the front of the container,the splitter on the back of the container. We got 5 models including the original model. By the simulation of the five models, we can know how the aerodynamic attachments influence the drag of the truck. After the computation and the analysis, we can see the aerodynamic attachments does work and reduce the drag. Finally the causation of the variation of the aerodynamic drag is also analyzed. The results and the analysis can offer some references to the project of drag reduction of the truck. And this will be the basic study of the drag reduction of truck.In this paper the model we used is based on the original date, and it's also be simplified. The characteristic of the original figure is kept to ensure the accuracy and reality of the simulation. The front face and the bumper of the truck are simplified,and the door and the cavity are simplified properly. The five models are divided into two groups. We get 5 models and the different aerodynamic attachments are mounted respectively based on the basic model. Model 1 is the basic model.Model 2 is based on model 1, the air shield and vanes are mounted. As the trailer we used is with a bed on the up of the cab, the postposition air shield is used when we chose the air shield. Model 3 is based on model 2 and the side safety panel is mounted on the middle of the container. Model 4 is based on model 3 and the splitters are mounted on the back of the container. Model 5 is based on model 4 and the splitters are mounted on the front of the container.As the 5 models we used are the endopleura models, so we can only chose half of the symmetric model to decrease the mesh numbers and the computational cost. The computational domain of the half truck shape simulation is a rectangular box shape whose total length is 7 times as the length of the truck model and total height is 4 times as the height of the model and the total width is 3 times as the width of the model. The distance between the front side of the box and the front end of the model is twice as the length of the model and 4 times as the length of the truck mode respectively. The domain is also composed of a small parallelepiped box and a large parallelepiped box, the tet-mesh is used to create the mesh. The RNG /k?εturbulence model is selected to simulate the flow field. Here follows the boundary condition: the velocity inlet boundary is used, and the velocity is set to be 28m/s just perpendicular to the wall of the inlet. The turbulence intensity is 2% and hydraulic diameter is 5.4 m. The outlet is the pressure outlet. The turbulence intensity is 2% and hydraulic diameter is 5.4 m.Through the computational result, we can get each aerodynamic force and its coefficient. In this paper we mainly study the aerodynamic drag of the truck. We can also get the vector graph of the velocity and the pressure distribution graph on any section. The aerodynamic characteristic is decided by the velocity of the flow and pressure around the truck. We can analyze the source of the aerodynamic drag by analyzing the velocity of the flow passing through the truck and the pressure distribution on the truck surface. And that can offer the gist to improve the aerodynamic characteristic of the truck. . Here follows the conclusions:1 For the heavy-duty truck with a container, the flow separates between the can and the container, it also separates under the container and at the back of the container. And that makes the vortex. So we should focus on these positions when we do the aerodynamic drag reduction.2 By mounted the air shield and the vanes on the back of the cab, the flow can be efficiently improved. And the vortex is decreased as well as the pressure the pressure on the front of the container. So the drag is reduced.3 By mounted the side safety panel under the container, the flow under the container can be improved. And that decreases the vortex at that position and reduces the drag.4 By mounted the splitters on the back of the container, the primary large vortex is divided into several small vortexes, as the velocity of the flow in the small vortex is smaller than in the primary large vortex, the pressure on the back of the container is augmented .So the drag is reduced.5 When we mounted the splitters on the front of the container, we can see that the vortex is divided into several small vortexes and the velocity between the panels is significantly greater than the surrounding flow thereby producing low pressure that acts on the container front face. Thus the pressure on the container front face decreases and the drag is reduced.