Is this solver really producing a steady state solution, is it showing variance with time???

Solution Modes in Autodesk CFD: Steady State vs Transient

https://www.youtube.com/watch?v=PVUFmYOyGkA 

Takeaways:
 -- Use Transient solver for things occurring over a time scale.
-- A steady state solution should look the same at different screenshots of the simulation.

Questions:
-- How do I calculate characteristic lengths?

"Transient Parameters :
Time Step Size:
-- Must be small enough to resolve flow and heat transfer detail
1/20th the time to required for the particle of fluid to traverse the characteristic length
-- 3 degrees rotation."
http://www.youtube.com/watch?v=PVUFmYOyGkA&t=15m48s

Also takeaway: The characteristic length is probably the width of the channel "b" that the air is exiting from.

If the residuals do not vary with time length, then this is a good sign of a steady state?

Also for a timescale consider the CFL number.
https://www.simscale.com/blog/2017/08/cfl-condition/
https://en.wikipedia.org/wiki/Courant%E2%80%93Friedrichs%E2%80%93Lewy_condition

 "You need a time step that is small enough to no affect your solution, but no finer"
http://www.youtube.com/watch?v=PVUFmYOyGkA&t=17m18s

"Allow the solution to converge at each time step"

OpenFOAM v6 User Guide: 4.3 Time and data input/output control

https://cfd.direct/openfoam/user-guide/v6-controldict/

https://www.openfoam.com/documentation/user-guide/standard-boundaryconditions.php

Standard solvers in OpenFoam:
https://www.openfoam.com/documentation/user-guide/standard-solvers.php

"
Time = 29.8

smoothSolver:  Solving for Ux, Initial residual = 0.017473, Final residual = 1.15283e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.00734311, Final residual = 2.32227e-07, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.00668358, Final residual = 2.10882e-07, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00352915, Final residual = 9.89991e-07, No Iterations 10
time step continuity errors : sum local = 2.90912e-08, global = -4.95109e-10, cumulative = 1.09353e-06
smoothSolver:  Solving for epsilon, Initial residual = 3.88718e-06, Final residual = 3.88718e-06, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 1.34953e-07, Final residual = 1.34953e-07, No Iterations 0
ExecutionTime = 8.87 s  ClockTime = 9 s

Time = 29.85

smoothSolver:  Solving for Ux, Initial residual = 0.0178206, Final residual = 1.18761e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.00734977, Final residual = 2.29515e-07, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.0066527, Final residual = 2.1099e-07, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00487037, Final residual = 6.93437e-07, No Iterations 11
time step continuity errors : sum local = 1.41454e-08, global = -4.01892e-11, cumulative = 1.09349e-06
smoothSolver:  Solving for epsilon, Initial residual = 3.88704e-06, Final residual = 3.88704e-06, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 1.34358e-07, Final residual = 1.34358e-07, No Iterations 0
ExecutionTime = 8.88 s  ClockTime = 9 s

Time = 29.9

smoothSolver:  Solving for Ux, Initial residual = 0.0171088, Final residual = 1.27743e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.00736379, Final residual = 2.29103e-07, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.00658612, Final residual = 2.10184e-07, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00551106, Final residual = 8.0959e-07, No Iterations 15
time step continuity errors : sum local = 1.49522e-08, global = -1.07481e-10, cumulative = 1.09338e-06
smoothSolver:  Solving for epsilon, Initial residual = 3.88686e-06, Final residual = 3.88686e-06, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 1.33787e-07, Final residual = 1.33787e-07, No Iterations 0
ExecutionTime = 8.89 s  ClockTime = 9 s

Time = 29.95

smoothSolver:  Solving for Ux, Initial residual = 0.0172835, Final residual = 1.37212e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.00735385, Final residual = 2.29564e-07, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.00652096, Final residual = 2.10925e-07, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00581243, Final residual = 9.67356e-07, No Iterations 19
time step continuity errors : sum local = 1.71268e-08, global = 1.81731e-10, cumulative = 1.09356e-06
smoothSolver:  Solving for epsilon, Initial residual = 3.88666e-06, Final residual = 3.88666e-06, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 1.33208e-07, Final residual = 1.33208e-07, No Iterations 0
ExecutionTime = 8.91 s  ClockTime = 9 s

Time = 30

smoothSolver:  Solving for Ux, Initial residual = 0.0172485, Final residual = 1.43144e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.00733651, Final residual = 2.31141e-07, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.00645853, Final residual = 2.11267e-07, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00658114, Final residual = 7.78764e-07, No Iterations 21
time step continuity errors : sum local = 1.3355e-08, global = -9.46949e-10, cumulative = 1.09262e-06
smoothSolver:  Solving for epsilon, Initial residual = 3.88643e-06, Final residual = 3.88643e-06, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 1.32581e-07, Final residual = 1.32581e-07, No Iterations 0
ExecutionTime = 8.93 s  ClockTime = 9 s

End
"
perhaps this relates, time Execution Time, and ClockTime. time is shown in Paraview. Using a timer tells me that the ClockTime is close to the time the simulation is running
https://stackoverflow.com/questions/7335920/what-specifically-are-wall-clock-time-user-cpu-time-and-system-cpu-time-in-uni

Compare this:

To the PitzDaily Case: