mapFields continuity error

wouterremmerie · September 24, 2014, 17:58

Hi all,

I would like to use the mapFiels feature to speed up calculations:
the flow around a fan or propeller needs a fine mesh, but in the end I'm only interested in the resulting flow. I would therefore cut out the propeller and only use its resulting speed & pressure field to calculate the flow in the rest of the domain.

Works in other software packages and could be done in OpenFOAM I think, using the mapFiels utility. This feature is used in the official cavity tutorial:
http://www.openfoam.org/docs/user/ca...#x5-350002.1.9
There they cut out a part of the geometry and the pressure and velocity fields are mapped onto the new, smaller domain. Works fine when you first reset the velocity on the walls to 0, which of course results in a zero net flux in or out of the domain --> no continuity error.

However, when you do not set the velocity to zero, continuity should still be ok, as you copy the results from an existing solution. But doing so (following the exact same steps of the tutorial except for the speed reset on the walls) leads to the following error:

Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 0.00433393
Specified mass inflow : 6.02285e-05
Specified mass outflow : 6.34605e-05
Adjustable mass outflow : 0

My guess is that the copying of velocity values is not performed exact enough and that leads to the small difference in mass inflow and outflow. But how could that be solved?

I'm thinking of maybe creating a small inlet/outlet patch in the domain, so that the solver can use that one to equalize the flow, but there should be a cleaner solution!

Does anyone have an idea?

Many thanks in advance for the help!

Regards,

Wouter.

mugabe2204 · November 20, 2017, 15:42

Hi Wouter,

Were you able to resolve this error later ?

It would be helpful if you can share your solution.

I am trying to convert the fixed Value ( zero) pressure outlet to fixed flux pressure or zerogradient and I have the simulation being run. When I tried to map to the test cases with new boundary conditions, it gives the same error.

Thanks in advance.

Cheers

wouterremmerie · November 22, 2017, 04:06

Hi Mugabe,

I did not solve the error at the time:
in the end, the calculation ran with high accuracy, so I did not need the mapFields anymore (not very efficient, but good enough...).

Hopefully you'll find it, best of luck!!!

Wouter.

September 24, 2014, 17:58	mapFields continuity error	#1
wouterremmerie Member Wouter Join Date: Aug 2013 Posts: 41 Rep Power: 13	Hi all, I would like to use the mapFiels feature to speed up calculations: the flow around a fan or propeller needs a fine mesh, but in the end I'm only interested in the resulting flow. I would therefore cut out the propeller and only use its resulting speed & pressure field to calculate the flow in the rest of the domain. Works in other software packages and could be done in OpenFOAM I think, using the mapFiels utility. This feature is used in the official cavity tutorial: http://www.openfoam.org/docs/user/ca...#x5-350002.1.9 There they cut out a part of the geometry and the pressure and velocity fields are mapped onto the new, smaller domain. Works fine when you first reset the velocity on the walls to 0, which of course results in a zero net flux in or out of the domain --> no continuity error. However, when you do not set the velocity to zero, continuity should still be ok, as you copy the results from an existing solution. But doing so (following the exact same steps of the tutorial except for the speed reset on the walls) leads to the following error: Continuity error cannot be removed by adjusting the outflow. Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow. Total flux : 0.00433393 Specified mass inflow : 6.02285e-05 Specified mass outflow : 6.34605e-05 Adjustable mass outflow : 0 My guess is that the copying of velocity values is not performed exact enough and that leads to the small difference in mass inflow and outflow. But how could that be solved? I'm thinking of maybe creating a small inlet/outlet patch in the domain, so that the solver can use that one to equalize the flow, but there should be a cleaner solution! Does anyone have an idea? Many thanks in advance for the help! Regards, Wouter.

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November 20, 2017, 15:42		#2
mugabe2204 New Member Bhanu Join Date: May 2014 Posts: 10 Rep Power: 12	Hi Wouter, Were you able to resolve this error later ? It would be helpful if you can share your solution. I am trying to convert the fixed Value ( zero) pressure outlet to fixed flux pressure or zerogradient and I have the simulation being run. When I tried to map to the test cases with new boundary conditions, it gives the same error. Thanks in advance. Cheers

November 22, 2017, 04:06		#3
wouterremmerie Member Wouter Join Date: Aug 2013 Posts: 41 Rep Power: 13	Hi Mugabe, I did not solve the error at the time: in the end, the calculation ran with high accuracy, so I did not need the mapFields anymore (not very efficient, but good enough...). Hopefully you'll find it, best of luck!!! Wouter.