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Aerodynamic vehicle design improvements require flow simulation driven iterative shape changes. The 3-D flow field simulations (CFD analysis) are not explicitly descriptive in providing the direction for aerodynamic shape changes (reducing drag force or increasing the down-force). In recent times, aerodynamic shape optimization using the adjoint method has been gaining more attention in the automotive industry. The traditional DOE (Design of Experiment) optimization method based on the shape parameters requires a large number of CFD flow simulations for obtaining design sensitivities of these shape parameters. The large number of CFD flow simulations can be significantly reduced if the adjoint method is applied. The main purpose of the present study is to demonstrate and validate the adjoint method for vehicle aerodynamic shape improvements.

The main objective of this work is to present an adjoint-based methodology to address combined optimization of drag force and cooling flow rate of an industrial vehicle. In order to cope with cooling effect, the volumetric flow rate is treated through a newly introduced cost function and the corresponding adjoint source term is derived. Also an alternative strategy is presented to tackle aerodynamic vehicle design improvement that relies on a so-called indirect force computation. The overall optimization is treated as a Multi-Objective problem and an original approach, called Optimize Both Favor One (OBFO), is introduced that allows selective emphasis on one or another objective without resorting to artificial cost function balancing. Finally, comparative results are presented to demonstrate the merit of the proposed methodology.

The recent Worldwide Harmonized Light Vehicles Test Procedure (WLTP) requirements have introduced additional challenges in the car development phase. Continuous demand for environmentally friendly road vehicles has lead all OEMs to minutely investigate any potential feature that could reduce C02 emissions. Comprehension of the aerodynamics of wheels, which are one of the least explored areas, can bring novel solutions for future car designs. As the capacity of experimental facilities is limited, the need for reliable CFD methods has become crucially important. Although computational resources are continuously growing, the number of CFD simulations is increasing even faster. Professionally supported CFD process based on open-source technology has recently become an appealing alternative to commercial codes.