Reflection BC for DO Model
 

Hi there,

I've a little question. Is there a boundary condition in OF(1.7 or what ever) that includes reflection of radiation?

I'm trying to use the DO model. Does anyone have some easy explanation of the Marshak Radiation BC?

Thanks and best regards
Jim

hi Jim,

Did you find anything?

This is all I know :

MarshakRadiation uses calculated temperature from the case as a temperature for deriving radiation intensity.


I need to understand how it does it, using which equations ?

No absorption of radiation boundary conditions present
 

Hi,

I was looking into OpenFOAM 1.7 and 2.1 to see if there are any boundary conditions which allow the temperature to rise as an effect of incident radiation from other boundaries. I was quite surprised to see that this is not already implemented?:eek:
Indeed it seems that all the OpenFOAM radiation models are meant for absorbing continua ... ?

If anyone knows hat I'm doing wrong - please comment.

at eh boundaries you may have, for instance:
the value in red is usually set to 1, meaning the surface won't reflect any radiation. In this case it will absorve 50% of what a blackbody would at the frequency. I guess this parameter is what you're looking for.. no? :confused:

Hi,

I think that the question about the BC that includes reflection of JimKnopf refers to "specular reflection". That is, if there is any BC that acts as a mirror, in this case a ray is defined as a vector (magnitud and direction) and the reflected ray will have a lower magnitud (part of it is absorbed) and will be reflected with the same angle of the incoming ray (Snell law of reflection). As far as I know there is not a BC implemented in Openfoam that can deal with this, but in the fvDOM model it could be implemented (I don't know how...)
If it is not the case, defining the emissivity as above is enough... in this case there is difusse reflection, that is, no matter the direction of the incoming ray, it will be reflected in all directions.

Regards,

There are boundaries that allow to do what you want, the zeroGradient boundary would act as a adiabatic surface, the fixedGradient allow to define a gradient in the wall (you have to calculate the value that adapt better to your problem) or the want I think works great, the groovyBC, it is not directly implemented, you can find more about it here
http://openfoamwiki.net/index.php/Contrib_groovyBC

regards

Hi Jim,

I am user of Fluent CFD software. And I want to try out the Openfoam for radiation modelling of irradiating lamp. In Fluent i can do this using he DO-model. Is it possible to simulate such a problem in Open-FOAM??
Can you please provide me some information on this. It would be great if you can guide me.

Thanks in advance.

Best Regards,

Novice

hi!
try searching for "fvDOM" inside the heatTransfer tutorials folder

i guess there's the hotroom tutorial you can work on. Most of settings are inside the constant folder in the "radiation" file.

you can find more about the settings with the combustion/flame tutorials.. just search for radiation inside the combustion file..

but here's a note and a question.. are you trying to model "light scattering"? (candelas..etc?) or just the influence of the radiation (heat?) myself havent tried modeling light in OF but i intend to .. as soon as i get some time :)

gl

Hi Mauricio,

Thanks for a quick response...
I want to model a UV lamp irradiation in side a closed vessel filled with water. My aim is to get the accumulated UV dose by the water at the outlet. In fluent I do this by modelling the flow first and then the UV intensity distribution with DO model and then get the dose accumulated by the water by multiplying the UV intesity with the time of irradiation.
Is it possible to do the same using OF.

Thanks in Advance.

well... i'm not an expert in radiation but i have this feeling...

radiation is a heat transfer physics.. then i guess you can try the buoyantSimpleRadiationFoam solver and use the discrete ordinate radiaton model..

set the fluid files and the radiation ones too..

try this pdf also http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2009/AlexeyVdovin/Radiation_in_OpenFoam_final.pdf

it might aid u with the settings

i'm assuming your running a steady-state case? yes?

in openfoam intensity is named "G" i guess.. its file, naturally is named G.

i guess you can try this solver then do the same calculation by hand, using this the results for the G variable and the time of exposure..

as for the settings of radiation themselves i can try to be of some help if you have any doubts concerning the sintaxe.. but i tell you u i'm not that good..lol

if you decided to give it a try maybe if you share you polymesh folder i can try to model it too on the weekend :p

sry i can't be of more help
gl