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Incorrect introduced mass in sprayFoam?

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Old   December 8, 2012, 07:33
Question Incorrect introduced mass in sprayFoam?
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Hi all,

When I run any case in sprayFoam (OF 2.1.x) the introduced mass after the end of injection is never equal to the specified totalMass in constant/sprayCloudProperties. This applies also to the unmodified aachenBomb case, the introduced mass grows over time and becomes constant at ~ 1.8mg whereas a value of 6.0mg is specified.

I am running the Sandia spray H constant-volume case, which is very similar to the tutorial aachenBomb. The case is non-reactive, with chemistry/combustion turned off. The liquid penetrations predicted by sprayFoam agree very well with the measured values. However the vapour length is way behind what you would see in the measurements: it is under-predicted by as much as two-thirds. Again the output shows the introduced mass as ~2.7mg, which is further confirmed by an integration of the term "rho*C7H16" in Paraview at the last time step (which is far beyond the end of injection). I have set totalMass = 17.8mg in the sprayCloudProperties.

I changed the totalMass (by a lot of trial and error) to 44.77mg, and the introduced mass comes close to 17.76mg and results are comparable. My mass flow rate profile for the spray H case is:
(
(0.0000 1.0)
(0.0068 1.0)
)

For the unmodified aachenBomb (2.1.x), totalMass 11.1mg results in injected mass ~ 6mg at the end.

I must be going wrong somewhere to have to resort to this. Am I missing or misunderstanding something, does the totalMass mean something else? How can I get the correct amount of mass into the system to get an acceptable vapour length?

(Pressure convergence criterion is absolute tolerance = 1E-06)

Regards,
Sushant

P.S. I calculate vapour length as the farthest cell along the injection axis that has C7H16 > 1E-06, directly in the solver by using a cell loop (very slow) or from Paraview's 'plot over line' after solving.
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Last edited by sushant; December 9, 2012 at 06:36. Reason: Pressure conv. criteria
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Old   December 8, 2012, 14:51
Default On 1.6-ext
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Dear all,

On OpenFOAM 1.6-ext dieselFoam does not have this problem, i.e. the injected amount matches the one specified.

However, the aachenBomb tutorial in 1.6-ext has 'mass' specified as 2mg. When this is increased to 6mg, the solver crashes midway because temperature (lower) goes below 200K and JANAF limits are crossed.

There was a discussion on the forum about replacing therm.dat (because C7H16 in it had a common-temperature of 1391K) with an entry that has a common-temperature of 1000K. I tried using this modified therm.dat (which by the way solves the issue with the reacting case on 2.1.x) but it does not help here.

I would really appreciate any suggestions as to where I am going wrong.

Best regards,
Sushant
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Old   January 10, 2013, 02:06
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hi sushant,

I also had same doubt as you posted here....
did u g get any clue taht how the mass flow rate profile in spray cloud properties is calculated?
it is also not matching with total mass
i addd all mass flow rate values as given n it comes around 211.89.

plz share if you had any idea

regards,
Pushkaraj
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Old   February 11, 2013, 12:18
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Hello pushkaraj,

Your problem is slightly different and hopefully easier to solve. You can search around on the forum, there are many posts about the specification of the mass flow rate profile including a very good explanation by niklas. It does not matter what the values add up to because it is normalized later by the totalMass.

My issue is that the totalMass specified is not attained at the end of the simulation: liquid mass + gas mass of fuel in the closed volume ends up much less than specified.

Regards,
Sushant
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Old   February 11, 2013, 12:26
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This is also seen on OpenFOAM 2.0.x (dieselFoam), integrating the fuel mass inside the closed volume (aachenBomb) much after the spray has all evaporated, falls well short of the specified totalMass: again ~1.8mg for 6mg specified.

I have tried tightening the pressure tolerance in both 2.0.x and 2.1.x but it doesn't seem to help. Does anyone have any idea where things are going wrong? I would really really appreciate any suggestions.

Regards,
Sushant
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Old   February 12, 2013, 09:25
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With regards to injection of mass, I had the same problem of a smaller amount being injected in OF2.1.x running sprayEngineFoam. I managed to solve the problem by reducing the parcelsPerSecond variable in the sprayCloudProperties file. Try reducing this value to 2e+6 and see what happens.

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Old   February 12, 2013, 11:55
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Hi ris,

This solves the issue! That's indeed what was wrong with my case setup.

Thanks a ton,
Sushant
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Old   March 19, 2013, 07:55
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Quote:
Originally Posted by sushant View Post
Hi ris,

This solves the issue! That's indeed what was wrong with my case setup.

Thanks a ton,
Sushant
Hi Sushant and Ris,

I am having the exact same problem. I ran my case perfectly in dieselFoam 20x but facing this issue after I migrate to sprayFoam 21x. That means the total number of parcel that can be injected is somehow constrained?

Please advise. Thanks in advance.

Carl.

Last edited by carl_xw4; March 19, 2013 at 08:31.
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Old   March 19, 2013, 10:28
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Hi Carl,

Change the parcelPersecond value in sprayCloudProperties to 200e+6 and reduce the minParticleMass in sprayCloudProperties to 1e-21. this will give you a larger number of parcels.

regards,

ris
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Old   March 19, 2013, 17:52
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Or you can use 2.2.x, where it should run without any changes needed. See: http://www.openfoam.org/mantisbt/view.php?id=785
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Old   May 26, 2013, 21:57
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Hi sushant,
can u pls share the "Sandia spray H constant-volume" case if you don't mind??
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Old   July 16, 2013, 20:10
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Quote:
Originally Posted by sushant View Post
Or you can use 2.2.x, where it should run without any changes needed. See: http://www.openfoam.org/mantisbt/view.php?id=785
Hi sushant,

Are you sure that the mass problem is resolved?
I'm trying to simulate spray H as well. The mass I'm injecting is 17.5mg.
It stops at somewhere around 13.4mg. I tried using both pressure driven velocity and flow rate profile. They both comes to almost the same result.

I'm using openfoam 2.2.x. Do you happen to know where the problem comes from?
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Old   August 2, 2013, 04:13
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At the moment i'm experiencing the same problem on my project. I'm using OpenFoam 2.2.x and the introduced mass is way off the value I specified in the sprayCloudProperties.

Are there any new informations about the problem?
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Old   August 8, 2013, 13:50
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After some trial and error i found out that unlike described in the OpenFoam-Wiki http://openfoamwiki.net/index.php/Co...ertiesNParcels
the amount of parcels have a great influence over the injected mass. Seems that the problem from OF 2.0.x reoccurred.
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Old   September 8, 2013, 00:20
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Does anyone happen to know why Aachen bomb is set to constant volume false and at the same time specific heat and density is set to a value resembles water?
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Old   May 29, 2014, 21:17
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Hello Ris
Sorry for bother you, but I have one similar problem and I read you're answer and seems correct for Sushant.
I want to change the mass in the spraycloudproperties the original mass is 6.0e-6 and I need to be 4.0e-5, 40 mg, and when I try to run the code, the code break saying FOAM Warning :
From function janafThermo<EquationOfState>::limit(const scalar T) const
in file /home/opencfd/OpenFOAM/OpenFOAM-2.2.2/src/thermophysicalModels/specie/lnInclude/janafThermoI.H at line 108
attempt to use janafThermo<EquationOfState> out of temperature range 200 -> 6000; T = 157.091

I trying changing, at you're advise, the parcels per second but the error continuous.
Any advice my friend.

Kind regards
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