Evolutionary Optimisation of an Exhaust Flow Element with Free Form Deformation

Evolutionary algorithms are well established methods for shape and design optimisations and they are applied to a large variety of problems. Especially for the optimisation of aerodynamic properties various publications demonstrate the potential of the method. Two major problems in the application of evolutionary optimisation methods for the improvement of aerodynamic properties are the representation of the shape and the generation of the CFD mesh necessary for the numerical flow simulations. In this paper a state-of-the-art deformation method named free-form deformation (FFD) is coupled with Evolution Strategies (ES). In this way, both problems are addressed. On the one hand the grid generation for solutions which are generated during the optimisation can be realised. On the other hand a representation of the design is generated, which decouple the complexity of the design to be optimised from the optimisation parameter. In this way it is possible to represent highly complex geometries with a tractable number of optimisation parameter. The combination of ES and FFD is applied to the optimisation of an exhaust flow element for a modern diesel engine. Especially the effects of the representation are demonstrated. Furthermore the problem of solution robustness is addressed in a way that multiple design points are considered during the optimisation in order to generate one optimal solution for a wide range of possible operation conditions.