How often do you use of CFD (Computational Fluid Dynamics) ?

I would have thought that astrophysics, being the study of the physical properties, behaviour, and interactions of celestial objects and phenomena, operates in the near-vacuum of space, and so would be one of vanishingly small, or non-existent, enthalpy.

 

Yes SailorAI, NS equations do not apply in interstellar media, but hypersonic phenomena are studied in the scope of planetary entry of objects. In laboratories also, hypersonic wind tunnels are used to simulate high energy phenomena in gaseous regions, to study their energy absorption/emission.