Three-Dimensional Fluid Topology Optimization and Validation of a Heat Exchanger With Turbulent Flow

The present work shows an innovative design framework for fluid Topology Optimization (TO) able to fully exploit the flexibility offered by Additive Manufacturing (AM) in the production of fluid-structure interaction systems. We present a geometry optimization method able to automatically design complex and efficient heat exchangers, adapted to maximizing fluid-structure heat transfer while minimizing turbulent flow pressure drop. The core of the method is the in-house Fluid Topology Optimization solver extended to include conjugate heat transfer problems. The TO method consists in emulating a sedimentation process inside an empty cavity in which a fluid dynamics problem is numerically solved. A design variable, in this case impermeability, is iteratively updated across the fluid dynamics domain. This mechanism leads to the formation of internal solid structures accordingly to a Lagrangian multi-objective optimization approach, adopted to include a multi-objective function. The solution of the optimization routine is the set of solidified structures, shaping the final optimized geometry. In order to match engineering applications, real conditions are implemented: an impermeability dependent thermal conductivity is included and a smoother operator is adopted to bound numerical thermal conductivity gradients across solid and fluid regions. The optimization is performed on a 3-dimensional straight duct: on the walls the temperature is constant and a coolant turbulent flow is simulated (Re 10000) inside the duct. The solver builds structures enhancing the heat transfer level between the walls of the domain and a coolant flow, by generating counter rotating vortices and complex fluid patterns. This is consistent to solution proposed in the open literature, such as v-shaped ribs, even if the geometry generated is more complex and efficient. The solution is validated with a high fidelity numerical simulation on StarCCM+, using a Detached Eddy Simulation (DES). Validation results shows higher heat transfer efficiency compared to the results present in the literature: the average Nusselt number computed on the domain walls is about 20% higher than the value obtained through experimental investigations on v-shape ribbed ducts. It is the first time that this method is applied and validated on real working conditions.