September 25, 2023 at 7:51 amCanh DoanSubscriber
I have a simple 2D mesh as the figure below.
I want to directly assign the laser intensity (W/m2) to a particular cell.
Is it possible in fluent?
If possible, how should I do it?
Thank you so much.
September 25, 2023 at 7:53 am
September 25, 2023 at 7:54 am
September 25, 2023 at 4:12 pmRobForum Moderator
Have a look at source terms.
September 27, 2023 at 4:08 amCanh DoanSubscriber
Hi Rob, thank you for your reply.
Can you explain more about source terms? I am a fresh student in this field so I might misunderstood your words.
September 27, 2023 at 5:26 amCanh DoanSubscriber
Hi Rob, Do you mean the DEFINE_SOURCE term is UDF code?
As the UDF manual, it is possible except for the discrete ordinates radiation model. However, as far as I know, the radiation heat transfer and the interaction between laser radiation and gas should use the DO model.
September 27, 2023 at 9:20 amRobForum Moderator
Yes, but you can assign a source term directly without needing a UDF or expression. For energy absorbion by the media you want DO or Monte Carlo radiation models.
If you just want to add energy into those cells (heat source) I'd split them out (register and separate option) and then use a fixed source term.
October 2, 2023 at 4:37 amCanh DoanSubscriber
I have tried to add directly the radiation source to a gas medium as you said. I set the divergence angle is 0 degree (collimated beam). But the result is a diverged beam as in the picture below. I don't understand why that happens because as theory, the radiation source go into a gas with a refractive index is 1 will not change direction. Can you help me correct it?
October 3, 2023 at 9:01 amRobForum Moderator
In 2d don't select any surfaces to display on, you'll get the contours then.
I suspect you're getting the beam (left) and that's warming the glass up (right). What conductivity did you set in the glass? Refine the mesh around the beam too - adaption may be a good choice.
October 3, 2023 at 11:32 am
October 3, 2023 at 12:27 pmRobForum Moderator
What did you set the divisions as in the main DO panel? You may find you need more mesh too - look at the resolution as the beam reaches the glass.
October 3, 2023 at 12:37 pmCanh DoanSubscriber
This is my DO model setting. I set only one band because I assume that my laser has only 1 wavelength is 1.07 um.
I just want to find the trend of the solution so I think a coarse mesh is better to save time.
I am curious that
- Could I set a collimating beam in my model?
- Could I assign the intensity to a particular cell inside the domain via UDF?
Please tell me is it possible or not?
Thank you so much
October 3, 2023 at 12:55 pm
October 3, 2023 at 1:03 pmRobForum Moderator
Increase the Discretisation. The DO model uses an angular discretisation and the default is a little low. Don't go over 3-4 or the cpu overhead gets excessive.
October 3, 2023 at 1:29 pmCanh DoanSubscriber
It doesn't work. I don't think it is a problem.
October 3, 2023 at 1:32 pmRobForum Moderator
Why do you need a wavelength band for one wavelength? What absorbtion coefficient is set?
October 3, 2023 at 2:28 pmCanh DoanSubscriber
It is only for a test case. My final target is a gas domain that absorbs laser irradiance and generates heat. Each gas has an absorption coefficient depending on wavelength so I need to indicate the wavelength band here.
The absorption coefficient was set in the air is 0 and glass is 0.05.
My target in the DO model is to make a collimating beam or a focusing beam into a gas domain. But up to now I cannot control the beam direction and divergence angle so I ask here.
Maybe you also don't know how to set a collimated beam inside a gas domain.
October 3, 2023 at 2:40 pmCanh DoanSubscriber
Hi Rob, is it possible by using the UDF code?
October 3, 2023 at 2:51 pmRobForum Moderator
Have you tried refining the mesh down the beam as well as increasing the discretisation?
October 3, 2023 at 4:47 pm
October 4, 2023 at 7:58 amRobForum Moderator
Is that with the angle on the beam as before?
October 4, 2023 at 12:01 pmCanh DoanSubscriber
Yes. I set 2 cases with the same angle.
October 4, 2023 at 1:00 pmRobForum Moderator
Rotate the domain by a degree or so. Then read the DO documentation to explain why.
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