• Density-based method
• Heat and mass transfer
• Multi-objective optimization
• Multi-physics field
• Topology optimization

With the increasing multi-functionality and integration of flow-related devices, the associated physical fields have evolved from single-flow fields to multi-physics fields. The characteristics of multi-physical fields and the multi-objective optimization problems involved increase the difficulty of structural design and pose new challenges to optimization methods. Traditional size and structure design methods, which often rely on trial-and-error methods based on the intuition and experience of designers, suffer from limitations such as long design cycles, low optimization freedom, and constrained performance improvement potential, and fail to address multi-objective trade-offs effectively. As a higher-level and efficient design methodology, topology optimization has been increasingly applied to various physical field problems, including structural mechanics, fluid dynamics, thermodynamics, and multi-physics coupling. In the context of technologies supporting green and low-carbon energy transitions, energy conversion systems and energy efficiency improvement technologies involving fluid flow and heat transfer are crucial. The design innovation and performance breakthroughs of efficient heat transfer, energy storage technology, hydrogen energy technology, and new energy equipment are all highly dependent on the application of fluid topology optimization methods.
The core of topology optimization lies in the optimization of material distribution within the design domain without relying on pre-defined initial structure or topology. Fluid topology optimization simultaneously optimizes and rearranges the topology, shape, and size of the design domain from a global perspective based on governing equations of flow and related multi-physics field, to achieve the expected optimization goals under specific constraints. Compared to size and shape optimization methods, topology optimization method enables higher degrees of design freedom, reduces dependence on experience, and broader optimization potential, enables the discovery of innovative structures. Thus, applying topology optimization to multi-physics field devices holds significant research value for improving multi-objective performance, enhancing energy efficiency, and revealing mechanisms of topology structure improvement. The main research contents of this paper are as follows:
1) A fluid-solid coupling multi-physics topology optimization model based on the density-based method is established, and a multi-objective topology optimization method to specific multi-physics field components is developed. To achieve the effective construction and accurate calculation of this model, a series of improvement methods are proposed: RAMP-type convex function and an exponential double interpolation function are developed for permeability in artificial porous media to change the distribution of design variables and reduce intermediate density regions; Helmholtz-type partial differential equations and an improved Heaviside projection function are introduced to filter and project design variables, eliminating the checkerboard structure and reducing the grid dependence; A transient sensitivity analysis model for phase-change heat transfer is constructed to solve the transient phase-change topology optimization model accurately; An ε-constraint multi-objective optimization model is proposed to solve the numerical oscillation and convergence difficulty of multi-objective collaborative solution.
2) The topology optimization design of flow channel in microchannel heat sinks is conducted, aiming to maximize heat transfer, minimize temperature variance, and minimize flow loss. The optimized structure and performance characteristics under bi-objective (heat transfer and flow loss) and three-objective (heat transfer, temperature uniformity, and flow loss) optimization scenarios are analyzed respectively. The ε-constraint multi-objective function is adopted to replace the traditional SAW method, significantly improving convergence efficiency and solution quality. The flow-guiding effect of the leading and trailing edge structures in optimized fins suppressed the formation of flow dead zones. The curvature variation of fin walls hindered the growth of low-speed boundary layers, and the irregular local arrangement and global multi-stage gradient distribution of fins interrupted the boundary layer development along the flow direction. These characteristics are the fundamental physical reasons for the improvement in comprehensive multi-objective performance.
3) The transient topology optimization model is established to enhance heat transfer in latent heat thermal energy storage units by optimizing fin structures. The optimization objectives are to maximize heat transfer rate and heat storage capacity within a specified time. Results revealed significant differences in optimized fin structures for pure paraffin and nanoparticle-paraffin, the optimized fins of pure paraffin evolve with longer lengths and more branches to compensate for its inferior thermal properties. The globally dispersed distribution and multi-branch characteristics of topology optimized fins substantially shortened heat conduction paths, regulated local convection regions, and improved overall heat transfer performance. Optimized fins reduced energy storage time by 68% compared to conventional fins.
4) A numerical model for activated carbon adsorption hydrogen storage tank is developed, incorporating the Darcy flow model, the modified Dubinin-Astakhov adsorption model with variable adsorption heat, and the multi-physics field governing equations of the adsorption process. A corresponding simplified topology optimization model is created to optimize fins of hydrogen storage tanks to enhance heat transfer. The effects of the structure and parameters of conventional fins and topology optimization fins on the hydrogen adsorption process, as well as heat transfer effect, are investigated. Fins significantly enhance heat conduction effect, allowing rapid temperature reduction of adjacent adsorption materials. The high specific surface area of optimized fins further improved heat transfer efficiency, promoted uniform hydrogen distribution, and strengthened convection effects along the axial center.
This study develops fluid topology optimization methods driven by multi-physics governing equations, focusing on the optimization design of multi-physics components. It aims to achieve innovative structures with comprehensive performance improvements, and reveal the synergistic influence mechanism of topology structure evolution on multi-physics field and multi-objective functions. This research provides novel design concepts and theoretical foundations for advancing the development of multi-physics component design methodologies.