Optimization Of Aerodynamic Drag Reduction For Flat-head Commercial Vehicles Considering The Influence Of Crosswind

With the rapid development of the automobile industry and highways,while enjoying the convenience brought by automobile civilization,people also have to face the two major problems of energy shortage and environmental protection.When a commercial vehicle runs on the highway,its aerodynamic drag directly affects fuel economy.Therefore increasing aerodynamic performance by reducing the aerodynamic drag of commercial vehicles has also received increasing attention.On the other hand,crosswinds often exist in natural conditions,and vehicles rarely drive in crosswinds with a fixed deflection angle of0~°.However,in previous related studies,whether with wind tunnel tests or CFD simulations,crosswinds were generally at angle of 0~°is used for aerodynamic research.However,the minimum aerodynamic drag of the car is usually obtained because the important effect of the crosswind on the change of the external flow field of the car is excluded,which will cause the effect of aerodynamic drag on fuel consumption to be underestimated.Therefore,it is of great significance to optimize the aerodynamic drag reduction of commercial vehicles in consideration of the influence of crosswind.In this paper,a flat-head heavy commercial vehicle in China is taken as the research object.By performing a wind tunnel test on a flat-head commercial vehicle model,and combining numerical simulation software STAR-CCM+to perform a numerical simulation analysis on a flat-head commercial vehicle,the results of the wind tunnel test and numerical simulation are compared and analyzed to verify the accuracy of the simulation,determine the simulation strategy and simulation scheme,and provide a simulation research basis for further studying the aerodynamic drag optimization of heavy commercial vehicles under the influence of crosswind.The numerical simulation of the truck model under the influence of different crosswind deflection angles is performed to analyze the flow state of the external flow field around the truck body under different crosswind deflection angles,so as to determine the cab and cargo box as the key parts for optimization,combined with the probability of crosswind distribution at different deflection angles,propose a weighted drag coefficient _dC as the evaluation index for optimization of drag reduction.Under the premise of ensuring that the geometry is similar to the real car model and the important basic dimensions are the same,the truck model is simplified.The simplified model of the truck is used as the optimization model.The 7 modeling parameters of the cab part and the 3 modeling parameters of the cargo box part are selected as Design variables.At the same time,two weighted drag coefficients and resistance coefficients at 0~°crosswind deflection angles are used as responses.A test design method further illustrates the need to consider the influence of crosswinds in the optimization process.The design manager project module integrated in STAR-CCM+is used to design the test parameters for optimization parameters using the Latin hypercube test design method.A total of 40samples were generated in the cab section and 16 samples were generated in the cargo box section,and were automatically simulated and calculated in STAR-CCM+.Based on the Isight platform,the Kriging approximate model was used to fit and combined with the adaptive simulated annealing optimization algorithm to optimize.Explore the correlation between the parameters and the response,and then get the optimal solution for drag reduction.The results show that the weighted drag coefficient decreased by 168counts after the optimization of the cab part,a decrease of 21.90%;the weighted drag coefficient after the optimization of the cargo box decreased by 94counts,a decrease of 12.25%,and the drag reduction effect was obvious.Finally,the proposed combination of optimization schemes was applied to a domestic commercial box truck,and numerical simulation was performed under different crosswind deflection angles.The weighted drag coefficient of the optimized truck model was C_d(28)0.492 The weighted drag coefficient decreased by 68counts,a decrease of 12.1%,and achieved a significant drag reduction effect.Combined with the analysis of the external flow field under different crosswind deflection angles before and after the optimization of the model,it further explained the inclination of the front window of the large cab and the rounded corners.Modeling parameters such as radius,approach angle,and container fillet have a significant impact on the aerodynamic performance of the vehicle.