A multi region adjoint-based solver for topology optimization in conjugate heat transfer problems

This work presents an exploration of fluid region optimization within coupled fluid–thermal problems of industrial significance, namely the design of a cooling plate for the thermal management of Printed Circuit Boards (PCB) of electrical propulsion systems. The Topology Optimization technique has been employed through a in-house developed multi-region adjoint solver and a set of customized boundary conditions, allowing the sensitivity computation independently on the problem size. The technique involves the integration of solid material into the computational domain to induce modifications in flow dynamics. This alteration aims to minimize a multi-objective function that considers both the skin temperature and the mechanical power dissipation caused by fluid movement across the domain. The obtained sensitivity values were then employed in optimizing material distribution through the Method of Moving Asymptotes. The derived material distribution was further post-processed to extract the newly optimized configuration of the system. This enabled a thorough evaluation of the optimization methodology's performance and its effectiveness in enhancing the system's overall efficiency

An Adjoint‐Based Solver with Adaptive Mesh Refinement For Efficient Design of Coupled Thermal‐Fluid Systems

A multi-objective continuous adjoint strategy based on the superposition of boundary functions for topology optimization of problems where the heat transfer must be enhanced and the dissipated mechanical power controlled at the same time, has been here implemented in a Finite Volume (FV), incompressible, steady flow solver supporting a dynamic Adaptive Mesh Refinement (AMR) strategy. The solver models the transition from fluid to solid by a porosity field, that appears in the form of penalization in the momentum equation; the material distribution is optimized by the Method of Moving Asymptotes (MMA). AMR is based on a hierarchical non-conforming h-refinement strategy and is applied together with a flux correction to enforce conservation across topology changes. It is shown that a proper choice of the refinement criterium favors a mesh-independent solution. Finally, a Pareto front built from the components of the objective function is used to find the best combination of the weights in the optimization cycle. Numerical experiments on two- and three-dimensional test cases, including the aero-thermal optimization of a simplified layout of a cooling system, have been used to validate the implemented methodology

Development of a VOF Dynamic Solver in OpenFOAM: an Application to the Simulation of the Opening and Closure Events in High Pressure GDI Injectors

The simulation of the primary liquid atomization in industrial geometries of atomizers for Gasoline Direct Injection (GDI) requires to accurately resolve the gas/liquid interface and time-resolved turbulence modeling. A dynamic multiphase volume-of-fluid (VOF) dynamic solver has been implemented in the OpenFOAM ® technology to simulate flow cavitation during needle opening and closure events. The solver is based on the extension of an already existing multiphase two-fluid model; it makes use of ad-hoc implemented cavitation sub-models and, with respect to the solver available in the official distribution of OpenFOAM, it includes some novel features: it is coupled to an advanced fully-automatic parallel mesh motion solver supporting topological changes of the mesh, where dynamic addition and removal of cell layers is performed to simulate the prescribed motion of the injector needle; also, needle opening and closure events are simulated by performing dynamic detach/attach of one mesh region into multiple regions. In the fluid-dynamic solver, a pressure-correction equation to enforce continuity after topological changes in the pressure-velocity coupling algorithm of the segregated solver and to to favor the solver convergence without compromising the accuracy of the solution. The resulting solver supports cavitation sub-models as well as LES and hybrid RANS/LES models for turbulence. Code validation is performed against standard test cases available from the litterature and against experiments

Vortex Flow and Cavitation in Liquid Injection: a Comparison between High-Fidelity CFD Simulations and Experimental Visualizations on Transparent Nozzle Replicas

Experimental instantaneous shadowgraph visualizations on transparent glass nozzle replicas of high-pressure fuel injectors have been used to validate a novel in-house high-fidelity LES-VOF multiphase solver, to study the evolution of vortex flow and fuel cavitation. Both experiments and simulations capture the formation of an unsteady vapor structure inside the nozzle volume, which is referred to as ‘string-cavitation’; strings are found at the core of the recirculation zones. High-fidelity simulations provide a very detailed insight into the vortex generation in the injector nozzle; strings appear within the time scales that are relevant for fast injection events (on the order of 0.1 milliseconds) and, for the problem under consideration, their generation seems mostly related to the flow pattern in the sac. It is also shown that vortexes interact, merge till they disrupt and favor the temporary inception of shear cavitation