  Multiphysics incompressible fluid dynamics simulations play a crucial role in
understanding intricate behaviors of many complex engineering systems that
involve interactions between solids, fluids, and various phases like liquid and
gas. Numerical modeling of these interactions has generated significant
research interest in recent decades and has led to the development of open
source simulation tools and commercial software products targeting specific
applications or general problem classes in computational fluid dynamics. As the
demand increases for these simulations to adapt to platform heterogeneity,
ensure composability between different physics models, and effectively utilize
inheritance within partial differentiation systems, a fundamental
reconsideration of numerical solver design becomes imperative. The discussion
presented in this paper emphasizes the importance of these considerations and
introduces the Flash-X approach as a potential solution. The software design
strategies outlined in the article serve as a guide for Flash-X developers,
providing insights into complexities associated with performance portability,
composability, and sustainable development. These strategies provide a
foundation for improving design of both new and existing simulation tools
grappling with these challenges. By incorporating the principles outlined in
the Flash-X approach, engineers and researchers can enhance the adaptability,
efficiency, and overall effectiveness of their numerical solvers in the
ever-evolving field of multiphysics simulations.
