[fix]|installexternal.py] Fix import of urllib.request

See merge request !2833

This changed to be the required way of importing the lib in some newer Python versions.
https://docs.python.org/3.9/library/urllib.request.html and https://bugs.python.org/issue36701 

[component] Allow specifying dynamic _or_ kinematic viscosity for constant components

See merge request !2832

Replace the IsOnWall function requirement with a boundary type

Closes #947

See merge request !2726

* For wall distance calculations use the call to boundary types

* collect the distance to a wall for each element
* collect the wall element's direction index

Feature/freeflow periodic

See merge request !2827

[material] Add option to PengRobinson::computeMolarVolume

See merge request !2831

Dmitry Pavlov authored 3 years ago and Timo Koch committed 3 years ago

- Ignoring the first two roots of the equation for Z in the
  smallest one is zero or negative. There was a comment
  documenting that behavior, but it was not implemented.

- Throwing NumericalProblem if no positive Z has been found
  or the number of roots is 2 or more than 3
  (no check was in place)

- Throwing NumericalProblem if the found molar volume turned
  out to be zero, negative, or NaN. (Replacing assert)

- Added handleUnphysicalPhase flag (true by default). If false, the
  single-root case is not checked for critical state of
  the fluid (otherwise, Michelsen test for a mix of
  hydrocarbons does not work).

[freeflow] Add mass/energy model and donea/channel/sincos test with new staggered

See merge request !2823

The condition leads to a velocity profile that spreads in all directions
at the outlet of a channel.