FLASH is organized into distinct code modules called ‘‘units’’ which, when put together, form the code basis for a simulation.
In general, the physics solvers view the unit managing the mesh, Grid unit, as a black box. The discretization, and most
of the solvers in FLASH, work in an Eulerian framework with the physical domain divided into blocks. Each block, surrounded
by appropriate layers of ghost cells presents a self contained computational domain to the Eulerian physics solvers in the
code [7]. Lagrangian particles do not fit directly into this framework because their movements reflect the nature of the flow
rather than the discretization or gridding method. For example, Fig. 1 shows trajectories of a few particles in a simulation of