There are many such problems:

1) Modelling of Cosmological background radiation

2) Simulation of multi-body Interactions: Granular Physics, Quantum Mechanics

3) Multi-phase Flow in Porous Media

4) Viscous fingering

5) Mixing of two different fluids

6) Turbulence and climate dynamics

...so on.

OpenFOAM - open set of utilities for the solution of continuum mechanics problems, including computational fluid dynamics (CFD). (https://en.wikipedia.org/wiki/OpenFOAM)

OpenFOAM has OpenMPI implementation for parallel running.

https://cfd.direct/openfoam/user-guide/running-applications-parallel/

OpenFOAM code is not easy to understand - but it would be helpful to start to work with physical modeling.

@Vikash Pandey and @Evgeniy avdeev :  Thanks. Your answers are very helpful