Viscosity

:For the image-editing utility, see: Viscosity (software)

Bulk viscosity

The trace of the stress tensor is often identified with the negative of one third of the thermodynamic pressure, which only depends upon the equilibrium state potentials like temperature and density. However, in general, the trace of the stress tensor is the sum of thermodynamic pressure contribution plus another contribution which is proportional to the divergence of the velocity field. This constant of proportionality is called the bulk viscosity.

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