Joint Research On Heavy-duty Truck Aerodynamic Characteristics And Stability Under Crosswind Effects

With the rapid development of Chinese high-grade highway network, the scale ofautomotive industry is expanding. In road transportation, heavy-duty trucks and othercommercial vehicles play an increasingly important role. In order to improve transportefficiency, the speed of heavy-duty truck is also increasing. Vehicles are often affected by theenvironmental crosswind driving on the highway, which is a significant impact on vehiclehandling stability and security, and may even lead to accidents. The study of heavy-dutytrucks handling and stability have important practical significance to ensure their drivingsafety under the influence of crosswind.In natural environment, wind is an important external factor affecting the vehiclescrosswind stability. In China, because of a vast territory, climate variability, anti-crosswindmonitoring system of the highway, railway and prevention means are not perfect, the naturalwind affect the vehicle facing the risk of the crosswind, the aerodynamic characteristics andthe handling and stability of vehicles will be affected due to the role of the crosswind.The shape of the heavy-duty truck is similar to rectangular, and the aspect ratio is large,which make the truck to be more sensitive to the crosswind effects. The study of theheavy-duty truck affected by the special conditions such as crosswind is helping to enhancethe heavy-duty truck vehicle performance. This paper was completed based on the researchof "Integrated Advanced Technology of Heavy-duty Truck Development", which was one ofkey projects "Eleventh Five-Year" National High-tech R&D Plan (863Plan) of China"Advanced Technology Vehicle Development". In this paper, wind tunnel tests,computational fluid dynamics methods and dynamics simulation method were integrated toresearch on aerodynamic characteristics and stability of domestic heavy-duty truck and to achieve the integration analysis of vehicle aerodynamics and vehicle system dynamics.According to the research needs of domestic heavy-duty truck crosswind stability,relative motion principle was applied to establish the research programs of crosswindaerodynamic characteristics, the two methods of wind tunnel experiments and numericalsimulation were adopted to study the aerodynamic characteristics of heavy-duty truck underthe crosswind effects. A heavy-duty truck1:7scale model was used in the wind tunnel test,the sideslip angle range was-15~+15deg of a total11kinds conditions of wind tunnel tests. Itwas deducted the interference of the support effectively on the test model in this test, and theconclusions were true and reliable. A heavy-duty truck1:1simulation model was establishedin the numerical simulation. In order to divide the mesh easily and improve meshingefficiency, cab, wheels, chassis of the vehicle model system were simplified reasonably. Thecomputational domain of the numerical simulation was generated, and the mesh scheme forcrosswind numerical simulation of heavy-duty truck based on the basic principles of meshgeneration was set up, the sideslip angle range was-30~+30deg, of a total21kindsconditions. The data of the numerical simulation were contrasted to tests under the sideslipangle range-15~+15deg conditions, and the data of the numerical simulation of21kindsconditions were proved to be effective and accurate.The aerodynamic characteristics of the vehicles under crosswind are different fromvehicles driving normally. Based on numerical simulation method, it was obtained theaerodynamic characteristics of heavy-duty truck under crosswind, and the flow visualizationwere shown, including body surface pressure, flow velocity in cross-section, iso-surface ofthe turbulent kinetic energy and stream lines. All of these results were analyzed andevaluated. This was also the preliminary judgment on the vehicle crosswind stability.In order to ensure that the data have smooth, continuous characteristics, vehicleaerodynamic parameters as six aerodynamic coefficients were curve fitted. The data wereboth kept the original state and coupled into the system dynamics software. In the nextdynamics modeling process, the crosswind virtual dynamic test could be completed byadding the aerodynamic forces.Using TruckSim to establish a digital vehicle dynamic model based on the parametersof vehicle assemblies. The road simulation test was taken with the digital vehicle modelwithout wind in the software environment. The vehicle model in TruckSim was versatile,real-time and scalability, and could reflect the real vehicle dynamics, by comparing with thereal vehicle testing on a variety of test conditions. So it could be used to do crosswindstability analysis.The classical three-DOF vehicle model under crosswind effects was generated, the characteristic parameters of the model were obtained from real vehicle after linearization, sothe crosswind stability of three-DOF vehicle model could be calculated and analyzed.Through contrasting analysis crosswind stability with the vehicle model in TruckSim, thetwo models crosswind response trends were shown, and quantitative analysis of theadvantages and disadvantages of different models were taken. As the words above applyingTruckSim to simulate the crosswind stability of the vehicle is more real and effective.The method of aerodynamic coefficients with different directions and different speedswas established based on the aerodynamic coefficients of vertical crosswind and the types ofthe crosswind were summed up. Considering the role of crosswind that may occur in real life,there were several aspects, the comparative analysis of heavy-duty truck driving with andwithout crosswind, the comparative analysis of heavy-duty truck stability in the open-looptest and closed-loop test with crosswind, the analysis of heavy-duty truck stability withdifferent crosswind speed, crosswind slope time, crosswind time, the analysis of heavy-dutytruck stability with different types of the crosswind and the analysis of heavy-duty truckstability with three typical crosswind. The joint research on vehicle aerodynamics andvehicle system dynamics came true, the comprehensive forecast of crosswind effects on thestability of the heavy-duty truck were achieved.In summary, it was researched on the crosswind aerodynamic characteristics andstability of the domestic heavy truck in this paper. Firstly, the shape characteristics of the realvehicle were considered, so the whole six aerodynamic coefficients were obtained by windtunnel tests and numerical simulation methods. The discrete numerical relationship betweensideslip angle and the six aerodynamic coefficients were converted to continuous variationcurve of six aerodynamic coefficients with sideslip angle by fitting optimization method. Sothe aerodynamic loading foundation of vehicle system dynamics model was based on theoptimization. Secondly, it was combined the vehicle aerodynamics and vehicle systemdynamics by six aerodynamics forces at the same reference point. So, the six aerodynamicforces, which were get from steady crosswind conditions were applied to vehicle systems toachieve a complete and valid judgment on the dynamic response of vehicle systems. Thirdly,the vehicle system dynamics model was established by detailed consideration of the internalparameters of the real vehicle, including vehicle tire characteristics, suspensioncharacteristics and steering system characteristics such as non-linear factors. The vehiclesystem dynamics model was validated to be more effective and accurate by the real vehicleexperiments and classic simplify vehicle models under crosswind. Finally, it was provided anew virtual test method to establish vehicle crosswind performance test method with fullconditions, high simulation, high-reliability. The method was more realistic to reflect theactual vehicle performance under the crosswind effects. Ideally, the driver behavior was researched and the driving habits were guided under crosswind by the results. This researchmethod is more applicable to the vehicle performance under crosswind effects forcorporation. The development of vehicle products will be more simple and easy. Not onlythe development cycle of vehicle will be shorten, but also the products will be increased themarket competitiveness.