Mean Age of Air

a_habib · February 25, 2017, 13:58

Dear Tian
Can you please answer my questions

HPE · February 7, 2021, 13:44

hope the following link can be helpful as well: Age of Air Function Object

Tobi · February 8, 2021, 07:55

One hint: the mean age of air is already implemented as object function in the Foundation version.

Off-Topic: Why do you set the diffusion to 1 and ignore the turbulent diffusivity? A diffusivity coefficient of 1 should be wrong here. Commonly, the diffusion mixing is based on the viscosity, so I would - at least - use the molecular viscosity of your fluid rather than 1 (as it is extreme large). Furthermore, I am not sure why a three year old thread is pushed up as there is no question anymore ? :P

HPE · February 8, 2021, 09:06

Hi,

Quote:

One hint: the mean age of air is already implemented as object function in the Foundation version.

Yes, true. It was a nice contribution of yours. That function object is, however, not available in the trademark openfoam(.com) and foam-extend at the time of writing. Just wanted to enable their users to be able to compute the local mean age of air, if need be. Plus, using the `scalarTransport` is rather more generic in my opinion. But I wish the age function object would be integrated into the others.

Quote:

Off-Topic: Why do you set the diffusion to 1 and ignore the turbulent diffusivity?

The numbers are not the default values. Anyone can change to anything, hence no reason.

Quote:

A diffusivity coefficient of 1 should be wrong here. Commonly, the diffusion mixing is based on the viscosity, so I would - at least - use the molecular viscosity of your fluid rather than 1 (as it is extreme large).

To my knowledge, that's not the diffusivity coefficient, DT which was defined as follows:

DT = alpha_v * nu + alpha_t * nu_t

`alpha_v` is 1, and `alpha_t` is 0, hence DT~nu (which is your suggestion) [I am more than happy to be proven incorrect].

Please note that there are different definitions of age of air metric in the literature (at least five to my review) since its introduction at 1981. Albeit slightly, each contradicts one another.

Quote:

Furthermore, I am not sure why a three year old thread is pushed up as there is no question anymore ? :P

Don't like CFD-Direct and its business practices. Try to emanate trademark-openfoam and foam-extend instead, and help their users in my free time. That's it :]

jaffa · January 7, 2022, 05:51

Hi Andersking,

Could you please explain how to use the attachment? Open it by using Fluent or CFD-post? Do I need to install Visual Studio? I am pretty new in this field so I am looking for help

Looking forward to your reply!

Thank you !

Tobi · January 7, 2022, 14:18

Quote:

Originally Posted by HPE

Don't like CFD-Direct and its business practices. Try to emanate trademark-openfoam and foam-extend instead, and help their users in my free time. That's it :]

Just one hint. The comfort and age function objects are also available in the ESI version v2112

HPE · January 7, 2022, 16:35

Thanks for the contributions, Tobi!

Here are the links of the FOs: age and comfort for those who are interested.

Lucc · November 8, 2022, 08:18

First, i'd like to thank you so much for your contribuition with this function implemented in OF!

My question is, what exactly is the value of the output of this function? I have simulated a room for 100s and when I go to paraView to see contours map of the age it shows values from 0 to 3500. My thought is that, on that instant, based on the velocity of each particle, is given as result the time in seconds that a particle takes from the inlet to get thar location. Is this right?

Thanks once again.

Tobi · November 10, 2022, 11:00

If you are simulating 100s , the max value can only be 100s. I think you are not simulation 100s but 100 iterations -> steadyState.

The outcome of the age field is the time it takes to refresh the cell with new fresh air.
Hence a value of 1000 would mean that the air stays there around 1000s.

Lucc · November 11, 2022, 05:51

Thank you for your reply!

I see. I'm running a simulation from 0 to 100s with a delta t of 0.01, thus 10000 iterations. The only thing is that i'm using pisoFoam algorithm (transient). In paraview displays a range of age from 0 to 3500, how could be this possible? Even if I'm running pisoFoam, could paraview be displaying the number of interation instead of seconds by default?

February 7, 2021, 13:44		#82
HPE Senior Member Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 12	hope the following link can be helpful as well: Age of Air Function Object __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

February 8, 2021, 07:55		#83
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	One hint: the mean age of air is already implemented as object function in the Foundation version. Off-Topic: Why do you set the diffusion to 1 and ignore the turbulent diffusivity? A diffusivity coefficient of 1 should be wrong here. Commonly, the diffusion mixing is based on the viscosity, so I would - at least - use the molecular viscosity of your fluid rather than 1 (as it is extreme large). Furthermore, I am not sure why a three year old thread is pushed up as there is no question anymore ? :P __________________ Keep foaming, Tobias Holzmann

January 7, 2022, 16:35		#87
HPE Senior Member Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 12	Thanks for the contributions, Tobi! Here are the links of the FOs: age and comfort for those who are interested. Tobi likes this. __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

November 10, 2022, 11:00		#89
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	If you are simulating 100s , the max value can only be 100s. I think you are not simulation 100s but 100 iterations -> steadyState. The outcome of the age field is the time it takes to refresh the cell with new fresh air. Hence a value of 1000 would mean that the air stays there around 1000s. __________________ Keep foaming, Tobias Holzmann

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February 25, 2017, 13:58		#81
a_habib Member Ahmad Habib Join Date: Nov 2014 Location: Aleppo, Syria Posts: 53 Rep Power: 11	Dear Tian Can you please answer my questions

January 7, 2022, 05:51		#85
jaffa New Member jingfu zhang Join Date: Jan 2022 Posts: 1 Rep Power: 0	Hi Andersking, Could you please explain how to use the attachment? Open it by using Fluent or CFD-post? Do I need to install Visual Studio? I am pretty new in this field so I am looking for help Looking forward to your reply! Thank you !

November 8, 2022, 08:18		#88
Lucc New Member gabriel rodrigues Join Date: Jan 2022 Posts: 10 Rep Power: 4	First, i'd like to thank you so much for your contribuition with this function implemented in OF! My question is, what exactly is the value of the output of this function? I have simulated a room for 100s and when I go to paraView to see contours map of the age it shows values from 0 to 3500. My thought is that, on that instant, based on the velocity of each particle, is given as result the time in seconds that a particle takes from the inlet to get thar location. Is this right? Thanks once again.

November 11, 2022, 05:51		#90
Lucc New Member gabriel rodrigues Join Date: Jan 2022 Posts: 10 Rep Power: 4	Thank you for your reply! I see. I'm running a simulation from 0 to 100s with a delta t of 0.01, thus 10000 iterations. The only thing is that i'm using pisoFoam algorithm (transient). In paraview displays a range of age from 0 to 3500, how could be this possible? Even if I'm running pisoFoam, could paraview be displaying the number of interation instead of seconds by default?