Automotive Exterior Shape Optimization Based On The Same Automotive Platform

Approximate optimization method is an efficient way to make a breakthrough at thebottlenecks of optimization of drag reduction for automotive exterior shape, and plays animportant role on solving highly nonlinear vehicle aerodynamic optimization problems. Inorder to reduce the evaluation index named as the CD A of a notchback CAS model in thispaper, an integrated optimization system, which is consisting of design of experiment,approximate surrogate model, optimization algorithm and co-simulation technology based onmulti-software, is established, while the stepwise optimization strategy is introduced andapplied to processes of optimization for exterior shape. Furthermore, based on the modulardesign concept of automobile platform, the significant influence of different chassis types onoptimization for aerodynamic shape is analyzed and the effect on aerodynamic performanceof automobile with different chassis types, rear suspension types or wheelbase issummarized.Firstly, a research on aerodynamic characteristic of the CAS model from an automobileenterprise is performed with computational fluid dynamics (CFD) according to the result ofgrid-independent validation. Meanwhile, automotive wind tunnel experiments on small-scalemodel of CAS are conducted as experimental verification for accuracy of simulation, whichis the data basis of numerical simulation in this article.Six parameters of design on aerodynamic exterior shape then are chosen as optimizedobjects as well as CD A is used for evaluation index to distinguish the aerodynamic performon the procedure of optimization for exterior shape of the CAS model with smooth chassis.This procedure is divided into two stages: global optimization of two-dimension automobilebody at first and then approximation optimization of detail of autobody. The stepwiseoptimization strategy is highly accurate and has a marked effect on CD A reduction which isup to13.01%.Moreover, the complex CAS model with detail of chassis is built. Based on the result ofCAS model with smooth chassis, aerodynamic optimization is performed on the complex model with detail of chassis employing integrated optimization system mentioned above.After the analysis of influence of chassis types on the aerodynamic characteristics ofautomobile, it is found that chassis types have a nonlinear effect on the aerodynamiccharacteristics although in the same styling of autobody, for which the optimal values ofdifferent design variables are varied in CAS models with different chassis types.At the last, based on the modular design concept and CAS models with complicatedchassis, two CAS model, one with independent rear suspension and the other usingnon-independent rear suspension, are made and valuable effect laws are given bysummarizing and analyzing the data or flow field from numerical simulation of four differentLayouts of chassis. Besides the optimization for aerodynamic characteristics of automobile,parametric design of chassis using wheelbase as design variable is applied to analyzing theaerodynamic characteristics of four CAS models with chassis types different in wheelbase. Adirect effect on the aerodynamic characteristics is found in this research as wheelbase lengthvaried. For the CAS models in this paper, it tends to have a better aerodynamic performancewith a long autobody as wheelbase and body length change at the same time or a shortwheelbase length as the body is invariant.All in all, with the effort in this paper, it is an effective means of processing an optimaldesign on automotive exterior shape of automobile and is also a useful attempt to studyparameterization of chassis and the effect of chassis types on aerodynamic characteristics ofautomobile.