Analysis And Optimization Of High-Speed Aerodynamic Stability Of A Tractor-Trailer Vehicle In Cross Winds

With the rapid development of domestic high-grade highways, soaring progress of the automotive industry and continuous increasement of vehicle running speed, higher and higher requirements are proposed on the performance of vehicles. If the vehicle subjects to high speed crosswinds while traveling at a high speed, its fuel economy, handling stability, driving safety and ride comfort will be significantly reduced. In extreme cases. it will lead to the vehicle’s deviation from the normal driving direction or even rollover. side slip, etc., triggering serious security-problems. In the meantime, for a tractor-trailer vehicle, however, its characteristics (large aspect ratio, high body height and center of gravity) and the light weight trend of vehicle design will exacerbate the vehicle’s crosswind sensitivity. Therefore, carrying out studies about the aerodynamic stability of the tractor-trailer vehicle under high-speed crosswind condition significant theoretical guidance and engineering application value on improving the vehicle’s fuel economy, driving safety and ride comfort.Considering structural features and working environment of the tractor-trailer vehicle, this paper intends to focus on the aerodynamic characteristics of the tractor-trailer vehicle under natural crosswinds and environmental crosswinds conditions, establish the multi-body dynamics models. analyze and evaluate its straight driving ability in the crosswind, optimize the aerodynamic characteristics and the straight driving ability, and then provide reliable theoretical basis and effective research methods for the improvement of the vehicle’s aerodynamic stability under crosswind condition. For this purpose, this paper, based on the notchback MIRA model universally applied in the whole world and the adjustable model used in the wind tunnel in Hunan Universitv. conducts a numerical simulation research on the aerodynamic characteristics of the vehicle under crosswind condition and wind tunnel test verification. and obtains a turbulence model and a method of the numerical simulations for the vehicle in natural crosswind condition. By using the above mentioned model and method. a simulated calculation is carried out on aerodynamic characteristics of tractor-trailer vehicle under different conditions of running speed and wind speed followed by another wind tunnel test to verity its correctness. and further the effect of additional features on aerodvnamic characteristics of tractor trailer vehicle is taken into account. Intensive research is made on the aerodynamic characteristics of tractor-trailer vehicle in environmental winds (in working conditions of overtaking and passing each other) by applying the technique of STAR-CD moving mesh. Safe driving for the tractor-trailer vehicle in the crosswind is studied and further the ADAMS multi-body dynamics model is established to carry out analysis and evaluation of empty tractor-trailer vehicle’s cornering performance under the action of crosswind. By utilizing Optimal Latin Hypercube sampling method and Kriging model to construct approximate model, this paper also conducts optimized research about the main parameters of wind deflector’s shape, which has great effect on the aerodynamic stability of tractor-trailer vehicle. The main research contents are as follows.1. Through the research of turbulence models and three simulation methods for vehicle aerodynamic characteristics under the condition of crosswind, we find that the third method and Realizable k-ε turbulence model can simulate vehicle’s aerodynamic characteristics very well under the action of steady and unsteady natural crosswind respectively:that wind tunnel six component measurement test and particle image velocimetry (PIV) test confirm the correctness of the proposed turbulence model and simulation method.2. Analysis results of tractor-trailer vehicle’s aerodynamic characteristics under crosswind condition show that the aerodynamic forces. moments and flow fields of tractor-trailer vehicle will be changed significantly under different crosswind conditions. Wind tunnel six component measurement test and surface pressure measurement test once again verify that the third method and Realizable k-e turbulence model can simulate tractor-trailer vehicle’s aerodynamic characteristics very well under the steady and unsteady crosswind conditions and that the change aerodynamic characteristics under crosswind condition is the key factor for the change of running characteristics under the same condition. The result also suggests that the drag force can be reduced by the additional devices obviously.3. The analysis results of tractor-trailer vehicle’s aerodvnamic characteristics under the working condition of overtaking and passing indicate that, in the process of overtaking and passing. with the increase of the relative velocity of two vehicles. the aerodynamic force is increased constantly; flow field around the vehicle in the process of overtaking and passing will generate mutual interference. causing the changes of turbulence. producing transient aerodynamic pressure distribution in the body of vehicle. and the pressure distribution will change rapidly in the process. 4. The safe driving research about the empty tractor-trailer vehicle suggest that the rollover is not likely to occur under strong gale; when driving on the ice load, the side slip may happen on condition that the running speed exceeds80km/h under breeze; and when under moderate gale, the lateral displacement value will exceed out of safety range at the very speed.5. The research results of aerodynamic stability of empty tractor-trailer vehicle under crosswind condition show that, the installation of wind deflector for tractor-trailer vehicle changes the aerodynamic characteristics and driving characteristics of the vehicle, and exerts an influence on fuel economy and driving safety. Therefore, taking the shape parameters of tractor-trailer vehicle’s wind deflector as design variables and the aerodynamic drag and lateral displacement of tractor-trailer vehicle under crosswind condition as design objectives. This paper applies Optimal Latin Hypercube sampling method to carry out the Design of Experiment (DOE). Based on the database of DOE. the Kriging approximate model is constructed and the fitting precision of the Kriging model is examined. Then, the Genetic Algorithms are used to optimize the shape of the wind deflector on the basis of Kriging model according to different optimization objectives. Optimization results show that after the optimization of wind deflector by taking aerodynamic drag of tractor-trailer vehicle under crosswind condition as the optimal objective, the aerodynamic drag of tractor-trailer vehicle installed with optimal wind deflector reduces by up to11.5%compared with that of tractor-trailer vehicle installed with the initial wind deflector:after the optimization by taking lateral displacement of tractor-trailer vehicle under crosswind condition as the optimal objective, the lateral displacement of tractor-trailer vehicle installed with optimal wind deflector is maximum10.05%lower:after the optimization by taking both aerodynamic drag and lateral displacement as optimal objectives at the same time, the aerodynamic drag of tractor-trailer vehicle installed with optimal wind deflector is maximum6.23%lower, and the lateral displacement maximum4.67%In conclusion. this paper systematically conducts an intensive study on the aerodynamic stability of vehicles in high-speed crosswinds and contributes valuable reference for thinking and approaches to the research on this subject.