Research On Heavy Commercial Vehicle Aerodynamic Drag Reduction Technology Based On Experimental Optimal Design

As the speed of heavy commercial vehicles increases,the energy used to overcome the aerodynamic drag also increases. Under the pressure of energy crisis and environmental protection, the inconsistency between the economy and efficiency has become serious. Aerodynamic drag of heavy commercial vehicles has tremendous impact on energy consumption, so the aerodynamic improvement has become an important direction for energy-save research.The main way to reduce aerodynamic drag of heavy commercial vehicles is to add aerodynamic devices. At present, research on drag reduction for a single device is popular; drag reduction research for several add-on devices is also increasing. However, the research on drag reduction effect of interactions between various devices is rare. In this paper, three popular deices: air shield,side extender and trailer flap are researched by experimental optimal design and numerical simulation techniques. The purpose of this paper is to get the single device with the optimal drag reduction performance and the combined performance of the three devices. The reasonable drag reduction plan will improve the fuel economy, reduce exhaust emissions and improve the market competitiveness of the heavy commercial vehicle.A domestic heavy commercial vehicle is taken for this study. The model is simulated by CFD software FLUENT and the simulation results will be compared with the wind tunnel test data to insure the accuracy of simulation model. After the model accuracy test, devices of different sizes or installation parameters were separately added to the heavy commercial vehicle to be simulated for optimal form and installation parameters of each device. After the separate research for every single device, those devices will be combined to the model. By the simulation of combined devices, the drag coefficient will show the device interaction effect on the overall drag reduction.Here follow the detailed research and conclusions: the drag coefficient is gotten by numerical simulation for the heavy commercial vehicle with the FLUENT and RNG k ??turbulence model. Jilin University tested the geometry similar model in the wind tunnel. There is a error of 4.8% between the drag coefficient of the numerical simulation and wind tunnel test value, which indicates that the simulation model is accurate.Three parameters of air shield is considered in this paper, which are the angle of the shield and the top plan of the cab,the length of the shield out of the back of the cab and the front width of the shield. Nine tests are designed with the tool of Orthogonal Design Principle. here follows the conclusion gotten by data analysis: the angle of the shield and the top plan of the cab greatly effect the drag reduction performance of the shield. When the angle matches well with the cab and the trailer, the flow separation will partly disappear, and the pressure of the front trailer reduces significantly, which leads to a aerodynamic drag improvement of 17.44%. When the angle matches, shields with different lengths out of the back of the cab have similar drag reduction performances. The structure that the front side of the shield tilts to the lengthways plan of the vehicle is helpful for guiding the air to the both sides of the box. When the gap between the cab and the trailer is large and the gap height is small, this design for heavy commercial vehicles on the improvement og aerodynamic performance is limited.Nine orthogonal tests were designed for the inclination and the lengthways length of the side extender. Simulation results shows that the side extender mainly impact the pressure of the back of the cab and the front of the trailer. The pressure drag change of the cab and the trailer is opposite with the use of the side extender, which means that there should be a tradeoff to get a whole drag reduction. The aerodynamic performance of the heavy commercial vehicle with a side extender alone is limited. In those tests, the model with the best side extender only reduces aerodynamic drag coefficient by 4.6%. Seven simulations with different angles of the trailer flaps show that the trailer flap impacts the form of the trailing vortex and determines the pressure of the trailer back. The trailer extender with the angle of 10°has the most significant drag reduction performance, which reduces the drag coefficient by 10%.The orthogonal tests of three factors and two levels were designed for the combination of the three devices. Results show that there are obvious interactions between devices. As the air shield exists, the drag reduction capacity of trailer extender decreases and the capacity of the side extender significantly increases. The best combination with additional devices reduces aerodynamic drag coefficient by 30%.According to the study of the additional devices and their combination, the drag reduction performance and the interaction between devices were assessed, which are helpful for drag reduction combination design of heavy commercial vehicles to make the best fuel economy and environmental standards possible. Experimental optimal design was used to arrange the simulation plan and data processing, which provides a method for similar researches with multi-factors and multi-levels.