[FLASH-USERS] Adding viscous term in the momentum equation

[Klaus Weide]

On Fri, 19 Jun 2020, Acharya, Nitish wrote:

> Does this work for a multi-fluid problem as well? Can i specify separate viscosities to each of the materials?

The relevant physics unit implementations that are advancing the solution 
(Hydro, Diffuse) aren't really "multi-fluid", at least in one common 
understanding of that term. FLASH with 3T support implements a single 
fluid (albeit with multiple components and potentially multiple 
materials). It is one fluid since the state (as represented in the 
solution vector field) has only a single shared velocity field.

You could implement viscous effects for this single fluid using a 
viscosity coefficient that depends directly on the local material 
composition. This would require a new implementation of the "Viscosity" 
material properties unit; in particular, a new implementation of 
"subroutine Viscosity".

Klaus