Adjoint topology optimisation of polymer melt flow channels producible by additive manufacturing

The design of polymer melt flow channels in extrusion lines remains challenging, leading to an increased use of optimisation algorithms. Additive manufacturing increases the degrees of freedom in flow channel design, but its manufacturing constraints must be considered. This thesis aims to investigate the potential of adjoint topology optimisation for designing polymer melt flow channels for specific optimisation objectives while ensuring additive manufacturability. This includes an investigation of the operating point dependency of the optimisation algorithm. An algorithm is developed to perform adjoint topology optimisation in OpenFOAM (OpenFOAM Foundation Ltd., London, UK). It uses an immersed boundary representation to enable quick adaptation of the geometry. The algorithm is extended with additional constraints ensuring additive manufacturability on non-cartesian meshes. Different optimisation objectives facilitate the targeted optimisation for minimal pressure drop or maximal flow balance, thermal mixing, or material mixing. The algorithm is demonstrated in two use cases. In the first use case, a static mixer is optimised for minimal pressure drop, maximal thermal mixing, and material mixing. The operating point dependency of the optimisation algorithm is investigated by evaluating the performance of the static mixers before and after optimisation for off-design operating points. The best candidate static mixers are manufactured and evaluated in lab trials. In the second use case, a simple L-profile extrusion die flow channel is optimised for either minimal pressure drop or maximal flow balance. The algorithm improves the flow channels' functionality with respect to their optimisation objective while ensuring suitability for additive manufacturing. In the static mixer use case, all optimisation objectives achieve a pressure drop reduction, which is confirmed qualitatively in lab trials. The optimisation results are independent of the operating point regarding the throughput and polymer material but highly dependent on the inlet inhomogeneity. Optimisation for minimal pressure drop is the most reliable independent of the operating point. In the extrusion die use case, both optimisation objectives reduce the pressure drop, but only the optimisation for flow balance improves flow balance. This research highlights the optimisation potential for individualised mixing elements and demonstrates the potential of adjoint topology optimisation as a method for designing the flow channels of complex profile extrusion dies.