Re: [sparta-users] [EXTERNAL] Validation chemical reactions in a box

[Gallis, M. A. <ma...@sa...>]

Marc

The equilibrium DSMC simulations maintain the gas at equilibrium, so there is no flow, transport or a transient. As said, all the code does is a numerical, Monte Carlo integration of the reaction cross section over the velocity distribution function.

You can easily calculate the reaction rate at equilibrium, for any reaction. You can just suspend product creation and energy release. The gas will stay at equilibrium and you just tally the reactions for any particular temperature.

So for example for O2+O2 -> O2 + O +O  just simulate : O2+O2 -> O2 + O2 with zero energy release.

Michael


From: Marc Vives Massana <mar...@kr...>
Date: Thursday, September 19, 2024 at 6:25 AM
To: Gallis, Michael A. <ma...@sa...>
Cc: spa...@li... <spa...@li...>
Subject: Re: [EXTERNAL] [sparta-users] Validation chemical reactions in a box
Dear Michael,

Thank you again for the clarifications! After reading more about what you suggested, I've realised that what I actually want to do is to compare the analytical QK model expression for reaction rates at equilibrium against the results from the DSMC simulation. This would effectively verify the set up and then compare the results with the experimental data you provided in your papers to validate for example.

Do you know a way to compute the reaction rates in equilibrium when using the QK model? Furthermore, is it possible to obtain an analytical expression for the transient properties in a "closed box" when using the QK model.

Thanks in advance,
Marc

El mié, 18 sept 2024 a las 0:51, Gallis, Michael A. (<ma...@sa...<mailto:ma...@sa...>>) escribió:
Marc

For the “closed box” cases like the one you are simulating the code works as a Monte Carlo integrator of the reaction probability over the velocity distribution function. For the TCE model the reaction probability is extracted from the reaction probability using an identical albeit analytical integration. So, if the code is not reproducing analytical results or is not in agreement with other codes, is because you are using different reaction rates. All these are clearly described in Bird 1994, Chapter 5. Make sure you are familiar this before you attempt any code-to-code comparisons.

The reaction rates that come with Sparta are taken from Park (1990). However, other authors have proposed different reaction rate sets. Thus, they are not unique nor are they supposed to agree with any other set.

For surface chemistry I think the NASA/Ames folk would be better positioned to answer your questions. None of the test cases in the 2015 tutorial included surface chemistry or gas phase chemistry validation.

Michael





From: Marc Vives Massana <mar...@kr...<mailto:mar...@kr...>>
Date: Tuesday, September 17, 2024 at 6:18 AM
To: Gallis, Michael A. <ma...@sa...<mailto:ma...@sa...>>
Cc: spa...@li...<mailto:spa...@li...> <spa...@li...<mailto:spa...@li...>>
Subject: Re: [EXTERNAL] [sparta-users] Validation chemical reactions in a box
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Dear Michael,

Thanks for the feedback. The comparison I'm trying to do is not only against other codes but also analytical data. Therefore, I took the reaction parameters described in sparta/examples/chem example which I believe is a similar case. My next question would be where the Arrhenius activation energy Ea, prefactor A, and exponent b, used in the example case are obtained from. Is a general database stating these parameters for all chemical reactions at different temperatures publicly available?

The next cases that I wanted to replicate are the validated test cases that were used to validate SPARTA and presented in the slides from the short course in 2015 available from the website. To better understand the chemical reactions taking place on the surface and to have a reference, is it possible to obtain the cases set up that were used for those validations?  This would validate the chemical reactions on the surface which requires some input data for the reactions that I'm struggling to find. Do you know where I can find reliable data for the reactions taking place on the surface?

Thanks in advance,
Marc

El jue, 12 sept 2024 a las 16:41, Gallis, Michael A. (<ma...@sa...<mailto:ma...@sa...>>) escribió:
Marc

This is a very interesting comparison you are trying to do. However, before you make a code-to-code comparison you need to make sure both codes are using the same molecular parameters, relaxation rates and most importantly reaction rates.

Michael

From: Marc Vives Massana <mar...@kr...<mailto:mar...@kr...>>
Date: Thursday, September 12, 2024 at 6:42 AM
To: spa...@li...<mailto:spa...@li...> <spa...@li...<mailto:spa...@li...>>
Subject: [EXTERNAL] [sparta-users] Validation chemical reactions in a box
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Dear SPARTA users,

I've been working on a validation case for the chemical reactions but the results are not as good as expected.

The case is based on the work done by Scanlon et al. (see: https://doi.org/10.2514/1.J053370) who were validating dsmcFoam. The case basically consists of a box of side length 1e-5 m with gas at 20.000 K and 0.0063 atm. The boundaries are specular and adiabatic walls. Initially, there is only O2 present in the box and only the dissociation reactions are considered:
O2 + O2 --> O + O + O2
O2 + O --> O + O + O

I tested the TCE and QK models and the results for the temperature and species fractions are not so good, see the figures below. Therefore, I kindly ask if someone could help me in implementing the chemical reactions or finding some validated cases with SPARTA so I could take a look at them.

Thanks in advance,
Marc Vives

I'll also leave the input file in case it helps:

## INITIALISATION ##

seed 12345
dimension 3

global gridcut 1e-5 comm/sort yes

global mem/limit 1024

units si

boundary        r r r


# PROBLEM DEFINITION ##

variable l equal 1e-5/2
create_box      -$l      $l       -$l      $l       -$l      $l
create_grid     10 10 10       block * * *

global          nrho 2.3118406573249943e+22 fnum 463

species         air.species O2 O
mixture         air O2 O vstream 0.0 0.0 0.0 temp 20000
mixture         air O2 frac 1.0
mixture         air O frac 0.0

create_particles air n 0

## SETTINGS ##

collide vss air air.vss
react tce air.tce

timestep        1e-9

## RUN ##

compute counts count O2 O
compute temp temp
fix output print 1 "$(step) $(c_temp) $(c_counts[1]) $(c_counts[2])" file output screen no

stats_style step np ncoll nreact c_temp

stats 1000

run 10000

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