DieselFoam spray model
 

Dear All,

I'd like to simulate diesel spray and ignition for
my diploma thesis . SInce im a beginner i want to run some test case like Aachenbomb.
Where can I find these test cases ?
or hat anyone some spray cases, and can you so kindly share with me?
qndfekjb@gmail.com

Thank you.
Sincerely,

Viliya

Hi,

there is a very good presentation detailing spray breakup using spray breakup models ETAB, TAB, CAB using ANSYS CFX, the presentation contains images of the spray development at specific instants as well as certain quantitative data. So you might check that out, it will be better to ensure that your models as correctly simulating the spray breakup and development before going for a combustion simulation.

You will find aachenBomb
OpenFOAM-1.5-dev:
https://openfoam-extend.svn.sourcefo...am/aachenBomb/
OpenFOAM-1.6-ext:
http://openfoam-extend.git.sourcefor...39082b;hb=HEAD

can you give some links about those presentation.I shall be highly greatfull.

thanks
shk

If you want to run diesel spray simulations in OF 2.1.x, be aware that the dieselSpray class has been deprecated and is not longer included. The new solver sprayFoam is now used, you can find the AachenBomb tutorial in $FOAM_TUTORIALS/lagrangian/sprayFoam/aachenBomb.

Be careful using sprayFoam.
Due that boiling is not included, the lagrangian spray model is only for low temperature effects.
Check this link: http://www.openfoam.org/mantisbt/view.php?id=346

not if you're using git, its been added

https://github.com/OpenFOAM/OpenFOAM...26abd04b29c583

Thank you very much niklas.
I did not know that

multi-hole nozzle
 

By the way.
Is there a multi-hole nozzle model (5 to 7).
So far I just used the coneNozzleInjection and did not found any multi-hole nozzle model (/src/lagrangian/intermediate/submodels/Kinematic/InjectionModel)

No there is no multihole injector available at the moment.

I have written my own injector though.
It works almost the same as the one available in the old dieselSpray library.
The difference is that it doesnt inject a parcel from each hole every time,
but it randomly picks one of the available holes to inject the parcel from.
That means that you should increase the injected parcels to get better
statistics and that you can have small differences in the injected mass
between the holes.

If you want to test it, you can unpack it under
src/lagrangian/intermediate/submodels/Kinematic/InjectionModel

and then, in the file
src/lagrangian/intermediate/parcels/include/makeReactingParcelInjectionModels.H

you add
#include "MultiHoleInjector.H"
to the include-statements

and a bit lower you add the MultiHoleInjection-line to the makeInjectionModel templates.

then its simplest to just do a wclean, wmake libso, in the intermediate directory, to recompile
the library with the new injector type.
You might have to recompile sprayFoam as well, but you will see that yourself
if the MultiHoleInjector doesnt appear among the available injector types)

Thank you very much niklas. I wiil have a look.
Actually do you use the "ORourke" stochasticCollisionModel.
If you use use, which coalescence is sensible. I do not really understand this value even though I had a look at the ORourke equations.

coalescence is just a boolean
so if you set it to on, parcels can coalesce,
if you set it to off, they will not exchange mass, only momentum.

Droplet coalescence when collision model is off
 

Dear Niklas,

I simulated a non-evaporating spray and turn off the collision model,
evaporation model, and heat transfer. I'm using TAB breakup model.
However, when I sample the number of droplets in axial direction over
a period of steady spray, I have a decrease in droplet number as shown
below (The number of droplet has been normalized, it is in the order of 1000).Is the decrease in droplet number due to coalescence?
Please comment.

Best,
Fairus

How can it be if it is turned off?
how do you do the sampling?

Once the number of parcel reached steady state, I start outputting the result over a period of time.
Than, I sample the droplets from each time directory according to their axial positions and the number of droplet is the same as the total number of parcel in respective axial position.

I'm not sure how the droplet number can be reduced. Obviously, we expect the droplet number to increase in axial direction since there is no means for it to decrease since evaporation and coalescense are off. No droplets are removed through the domain boundaries between the spray BC location and
the outlet.

Fairus

how do you do the sampling?
code please

Niklas,

I'm using the following shell scripts to do the sampling. There are 2 main scripts that need to be run in the following sequence:

1) from the case directory:

./runppc2Atom (sample and put droplets in different axial positions in "ppd" folder)

2) from the ppd folder:
./breakupDropletSample (output the number of droplet vs axial position)

Sorry if it appears a bit untidy. I've to separate them because the script need to serve multiple purposes, so I need to have them separated.

Fairus

Hey mfmohdyasin, Usually for cfd codes involving sprays and specifically breakup models, its very costly to simulate a droplet with a diameter with order say for e.g 1E-6, and its rather pointless. With brekaup models, hundreds of these small droplets would be produced especially if your spray is supposed to be steady state. So if a droplet get to this size, the code usually adds its mass and momentum to the continuous phase and subsequently removes it from the computation.

This might explain what you are seeing. Look for some sort of parameter in openfoam that specifies a minimum droplet diameter before removal from domain. Myt be better to look into D10 and D32 droplet diameters sampled across your domain space.

Also are you counting droplet parcels (the lagrangian objects) or the number of real droplets contained within each parcel?? Breakup models modify the latter parameter depending on the new droplet diameter computed via the breakup model procedure in order to conserve mass in the parcel.