Re: [sparta-users] Fw: Fix Ambipolar Question

[Runco, J. J C. U. A. AFIT/E. <Joh...@af...>]

Chonglin,


Thank you for the response.


(1) Good catch! I did not notice they did not add to 1. I will adjust that accordingly while neglecting the other trace species in air (Argon, etc)


(2) It looks like SPARTA does not support recombination reactions only when using fix ambipolar. Though, the air.tce file doesn't look like it has any recombination reactions the way it is. I'm guessing you can hand code those recombination reactions and comment out fix ambipolar commands from the input code in order to incorporate recombination reactions. For my current problem, I am neglecting all ions except NO+, so the only recombination reaction that would be important for me is

NO+ + e --> N + O

R A 0.0  0.000000  1.4945e-11   -.65    4.404e-19   (Found the reaction coefficients from scholarly literature)


(3) I think surface reactions may have a negligible effect on the overall electron density even with  surface recombination reactions, but I'm not certain. Thanks for pointing that out though.


(4) I mentioned this to Steve as well: I don't think the reaction file has N+ + O2 -> N + O2+  in the air.tce file. Is this a mistake?


Friendly regards,

John


________________________________
From: Chonglin Zhang <zha...@gm...>
Sent: Thursday, November 15, 2018 8:33:21 PM
To: Runco, John J Capt USAF AETC AFIT/ENY
Cc: spa...@li...; sj...@gm...; sj...@sa...
Subject: Re: Fw: [sparta-users] Fix Ambipolar Question

Hi John,

(1) In your input script, you have N2 fraction 0.7809, O2 fraction 0.2095. The sum is not 1. If this is the case, then there will be N, O, NO, NO+ generated from the inlet boundary (although the inlet temperature is only 196.7K in your case). Is there any reason you want to do this? This might increase the overall density of N, O, NO, NO+, possibly resulting in more electron to be generated through reactions such as:
N + N -> N2+ + e, O + O -> O2+ + e, N + O -> NO+ + e, etc. You could look at the "air.tce" file to see which reactions will generate electron.

(2) Also, as you mentioned, there is no recombination reactions modeled in SPARTA, this could also cause a higher electron density.

(3) Similarly, you could also consider adding surface reaction in your script. If N, O, NO, NO+, and electron recombine on the surface, it will also reduce your overall electron density.


Thanks!
Chonglin

On Fri, Nov 9, 2018 at 2:51 PM Runco, John J Capt USAF AETC AFIT/ENY <Joh...@af...<mailto:Joh...@af...>> wrote:
All,


A couple of other ideas that I thought could be the issue:


3. From the documentation,

"Ambipolar recombination reactions must be in the following order:

A+ + e -> A

IMPORTANT NOTE: Ambipolar recombination reactions are not yet supported in SPARTA."


Could this be the cause of my electron density computations being a couple orders of magnitude greater than the experimental data?



4.If I am trying to find electron densities on orders of magnitude 1e16-1e18 and my fnum value is 3.9e16, I'm thinking it will not capture all of the data correctly if the ratio of physical particles to simulation particles is slightly greater than the lower end of the experimental data I am trying to match. I currently have a couple of jobs in queue that have an fnum of 3.9e15.


Thanks again for any help,

Appreciate you answering my many questions.

John, Sparta User



________________________________
From: Runco, John J Capt USAF AETC AFIT/ENY <Joh...@af...<mailto:Joh...@af...>>
Sent: Thursday, November 8, 2018 2:05 PM
To: Chonglin Zhang; spa...@li...<mailto:spa...@li...>; Steve Plimpton; 'sj...@sa...<mailto:sj...@sa...>'
Subject: Re: [sparta-users] Fix Ambipolar Question

Chonglin/Steve,


I am currently still getting electron densities higher than the experimental data indicates (about 3 orders of magnitude). I think I am coding the fix ambipolar correctly, but was hoping to get a second pair of eyes on it to see if I was missing anything. Attached is my input dec. Highlighted in yellow are the lines that have to do with the fix ambipolar commands. I took the manual's suggestions as well and made 2 different mixtures, one with the electron and one without. I used a fix in/emit for the mixture without the electrons, and subsequently a collide command for a mixture with all the species.


Mistakes that I think are possible:

1. incorrect coding for the creation of two different groups (ion and electron) within the mixture containing all species...as the Sparta manual suggests?:

mixture air_wo_ID NO+ e group self


I am currently trying to run a job using two separate lines to distinguish the electron and ion (NO+) within the group that contains all the species:

mixture             air_wo_ID NO+ group ion_ID
mixture             air_wo_ID e group elec_ID


2. not varying the initial electron velocity used in the mixture command seen below? (don't think this is the issue due to the air.species and air.vss and air.tce files, but it came to mind).
species             air.species N2 O2 N O NO NO+ e
mixture             air_wo_ID N2 O2 N O NO NO+ e vstream 7650. 0. 0. temp 196.7

Appreciate the help,
John
Sparta User



________________________________
From: Chonglin Zhang <zha...@gm...<mailto:zha...@gm...>>
Sent: Thursday, October 11, 2018 2:05 PM
To: Runco, John J Capt USAF AETC AFIT/ENY
Cc: spa...@li...<mailto:spa...@li...>
Subject: Re: [sparta-users] Fix Ambipolar Question

Yes, if you are modeling electron density, then you need to use the "fix ambipolar" command, together with "collide_modify" command.

You will need to do something like this:

collide_modify   vibrate smooth  ambipolar yes        # active the ambipolar approximation for ionization reactions.
fix  ID  ambipolar   e NO+ N+ O+ N2+ O2+              # set which species is electron, which species are ions; ID is the fix id number.


Thanks!
Chonglin

On Thu, Oct 11, 2018 at 1:42 PM Runco, John J Capt USAF AETC AFIT/ENY <Joh...@af...<mailto:Joh...@af...><mailto:Joh...@af...<mailto:Joh...@af...>>> wrote:
If I am looking to verify electron densities, would accuracy also depend on incorporating the fix ambipolar command?


Thanks,

John




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