Adjoint-based sensitivity maps for drag optimization of a passenger car

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(1)ADJOINT-BASED SENSITIVITY MAPS FOR DRAG OPTIMIZATION OF A PASSENGER CAR Carsten Othmer†, Guillaume Pierrot‡, Philippe Ravier‡ and Ming Zhu‡ †. Volkswagen AG Numerical Analysis E1, Letter box 1697 D-38436 Wolfsburg, Germany e-mail: carsten.othmer@volkswagen.de ‡. ESI Group SA Rungis, France. ABSTRACT Nowadays there is a clear requirement in the automotive industry for automated geometry optimization processes for part design. The current optimization techniques that are used and already integrated into the design process, are mainly robust black box methods of the bionic type, i.e. genetic algorithms and evolutionary strategies. Their computational cost, however, poses a strong limit on the allowable complexity of the optimization problem, and some tasks such as the aerodynamic optimization of a whole car are simply unfeasible with this kind of techniques. As an alternative, adjoint-based optimization has been recognized to be efficient for such tasks. While already established in the aerospace sector, only recently adjoint-based optimization is entering the development process in the automotive industry. Applications are so far limited to feasibility studies and focus on the use of continuous adjoints for shape optimization of climate channels [1-3] and the computation of topological sensitivities via automatic differentiation [4,5]. Now, however, the availability of a professional adjoint solver in ESI's PAM-FLOW CFD code opens the possibility of more sophisticated applications. In the present study, this adjoint solver is for the first time applied to a surface mesh representation of a complete production passenger car. A sensitivity map with respect to aerodynamic drag is computed and discussed in detail. It allows to identify those regions of significant optimization potential at the same time where shape changes do not significantly alter the design. Such sensitivity maps for automotive applications have not been available so far, and we conclude that they constitute an efficient and powerful tool for aerodynamic fine-tuning of cars that we have just started to explore. REFERENCES [1] C. Othmer, Black Box, Adjoint and Topology: Three options for CFD optimization, NAFEMS CFD Seminar, Wiesbaden, 2005. [2] C. Othmer and Th. Grahs, Approaches to fluid dynamic optimization in the car development process, EUROGEN 2005, Munich, 2005. [3] C. Othmer, Ph. Ravier, and G. Pierrot, Adjoint methods for automotive CFD optimization, PUCA 2005, Tokyo, 2005. [4] Th. Kaminski, R. Giering, and C. Othmer, Topological design based on highly efficient adjoints generated by automatic differentiation, ERCOFTAC Design Optimization Conf., Las Palmas, 2006. [5] C. Othmer, Th. Kaminski, and R. Giering, Computation of topological sensitivities in fluid dynamics: Cost function versatility, ECCOMAS CFD 2006, Delft, 2006..

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