| Vehicle aerodynamic resistance has significant impacts on fuel consumption and emissions and driving range of electric vehicles.The traditional methods of reducing aerodynamic resistance by optimizing components such as the air intake grille,rearview mirror,and diffuser have encountered bottlenecks.The flow filed instability around the wheel is mainly originated from the influence of the tire,rim and body fender,and it will further impact the vehicle aerodynamics.The wheel region,which accounts for up to 25% of the vehicle aerodynamic resistance,has become one of the key research contents in the development of energy-saving,environmental protection,and low-wind resistance vehicles.In this paper,with the support of the National Natural Science Foundation of China(NSFC),we conducted the analysis of the flow loss characteristics in the wheel region based on numerical simulations and experiments,and grasped the influence of wind speed,tire outer contour and spoke opening ratio on the flow instability in the wheel region.Based on the concept of flow field control,the study of optimizing the aerodynamic shape of tire profile,wheel rim and body fender was carried out.It provides a method for improving the aerodynamic characteristics of the whole vehicle and a foundation for the efficiency of vehicle resistance reduction and technological innovation.The main research contents and achievements of this works are as following:(1)Ahmed body marked by the features of reasonable abstraction and simplification for the real cars,and it is widely selected as a research object in academia and industry.Based on Ahmed model,the aerodynamic characteristics of Ahmed model are simulated and analyzed.The reliability of the aerodynamic characteristics simulation method is verified by the test results.The method of constructing the whole vehicle model by adding rotating wheels to Ahmed model is proposed on this basis.The whole vehicle model is created by using 3D printing technology,and the wheel rotation is driven by controlling the motor rotation.The wind tunnel test and simulation analysis of aerodynamic characteristics of the whole vehicle model are carried out.By comparing the pressure results of the wheel cavity area and the tail section,the effectiveness of the simulation method of the aerodynamic characteristics of the whole vehicle model was verified.(2)The differences between the flow field characteristics of the Ahmed model and the whole vehicle model were compared and analyzed,and the mechanism of the influence of the presence of rotating wheels on the aerodynamic characteristics of the whole vehicle model was clarified.The entropy yield theory was applied to quantitatively evaluate the flow loss of the whole vehicle model.The characteristics of the entropy yield distribution in the wheel area and body area under different wind speeds were analyzed,the results show the local entropy values in the airflow direction tends to increase first,then decrease,and then increase again;that local local entropy values of the front wheel are higher than that of the rear wheel.Further,the correlation between the flow field characteristics and the entropy yield distribution was studied,and the mechanism of the flow loss in the rotating wheel area was clarified.(3)In order to clarify the flow instability in the rotating wheel region,the influence of wind speed,tire outer profile and spoke opening ratio on the pressure and velocity fields in the rotating wheel region are compared and analyzed.The influence law of wind speed,tire outer profile and spoke opening ratio on the aerodynamic resistance of the whole vehicle is studied.The pressure pulsation characteristics of different measurement points in the wheel cavity of the front and rear wheels are systematically analyzed,and the significant location of the flow instability in the wheel cavity is clarified.The pressure pulsation characteristics of different measurement points in the wheel cavity of the front and rear wheels are systematically analyzed and the sensitive location of the flow instability in the wheel cavity is clarified.(4)With the aim of improving the flow stability in the wheel area,the effects of the design parameters of the tire outer profile and the design parameters of the rim and spoke opening shape on the flow instability in the wheel area were investigated.The influence law of different design parameters on the isolated wheel aerodynamic resistance was obtained.The aerodynamic profile optimization of the tire outer profile and the spoke opening shape was realized on the basis of the approximation model and the intelligent optimization algorithm,and the comparative analysis of the aerodynamic profile before and after the optimization of the wheel area and the whole vehicle was carried out.The difference of the flow field characteristics of the wheel region and the whole vehicle before and after the optimization is compared and analyzed.Based on correlation coefficient analysis results,it is confirmed that the tire aerodynamic characteristics and the rim aerodynamic characteristics are independent of the whole vehicle aerodynamic characteristics.(5)In view of the fact that the front-end blunt body design of the Ahmed model is difficult to realize the flow guide of the vehicle body wing and clarify the influence mechanism of the body wing construction on the aerodynamic characteristics of the wheel area.The China Automotive Engineering Research Institute(China Automotive Research Institute)CAERI Aero,taken the standard model as the object,the simulation analysis of the aerodynamic characteristics of the whole vehicle was carried out,and the reliability of the simulation method was verified by the aerodynamic drag coefficient.According to the shape characteristics of the fender surface,a fender test design method based on the free deformation method was proposed,and then used Optimal hyper-Latin test method,radial basis neural network model and multi-island genetic optimization algorithm,carried out the research on the optimization method of aerodynamic drag reduction of the body fender;Compared and analyzed the wheel surface pressure and wheel cavity velocity distribution before and after the optimization of the fender,the eddy current structure in the wheel area and the variability of the local entropy production value reveal the realization mechanism of improving the aerodynamic characteristics of the vehicle by affecting the unsteady flow characteristics in the wheel area. |
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