Simulating continuous laser at a point in a domain?

Sorabh · July 27, 2018, 04:43

Hello,

I am trying to implement a scenario in Fluent where a continuous laser hits a point on a 5mm X 25mm tissue piece. I have applied this method:

https://imgur.com/HBjiDE2

If you follow the aforementioned image, the laser will hit the small 0.1x0.1 mm square and the heat generated by the laser will then warm up the surrounding zone. That is the general idea.

In order to do this, I made a 2D 5mmx25mm surface body in design modeller, followed by four points, and then a new line body from the four points, and finally a new surface body from the line body that I created.

https://imgur.com/6BDy4ix
(this image depicts the four points,lines and the resulting surface)

On applying heat flux(a substitute for laser heating) on the surface body, the FLUENT results show that only that surface body is heated, and that the surrounding domain has not been affected at all.

Is this approach correct? If yes, then what should I do to remedy the aforementioned scenario?

Any help or advice will be highly appreciated. Thank you.

LuckyTran · July 27, 2018, 10:31

The surface heat flux idea to a small surface is correct. You just have to figure out what's wrong with your setup. Can you describe the rest of it? i.e. what the final mesh looks like, # cell zones, etc.

Sorabh · July 27, 2018, 12:03

Quote:

Originally Posted by LuckyTran

The surface heat flux idea to a small surface is correct. You just have to figure out what's wrong with your setup. Can you describe the rest of it? i.e. what the final mesh looks like, # cell zones, etc.

Thanks for the reply, and yes of course. (It will be a long read, so bear with me please!)

First up is the mesh, this is what it looks like:

(A standard mesh with a mesh refinement value of 3)

While making the new surface, a contact region was established:

You can observe the main domain and the new, small surface.

In the FLUENT solver, this is what the general setup looks like:

I switched on the Energy Model for this problem.
In materials, I applied a new 'Tissue' material, with density and specific heat varying linearly with temperature.

Now, because of the contact established above, there are now 2 cell zones:

Here, the 'contact-region-src' refers to the larger area; while 'contact_region-trg' refers to the smaller area where flux is being provided.

Now, for the boundary conditions:

The 'interior-contact_region-src' is of the type interior. (The bigger domain)
While the 'surface-body'(the smaller section) is of the type wall. A heat flux of 5e08 W/m2 is applied onto it.

After initialization, and running the calculations, I get the following results:

The solution neither converges nor diverges! Also, in the console of the solver, the message "Temperature limited to 5e+03 in 1 cells on zone23 in domain1" keeps appearing, repeatedly after each iteration! (zone23 refers to the smaller surface)

This is all the info I have at the moment. I am currently a newbie, so I hope I dont test a lot of your patience!!

AlexanderZ · July 30, 2018, 00:44

switch to TRANSIENT solver
looks like you do not need any contacts here
my opinion: to simulate laser welding heat source is applied in most cases, not the heat flux

best regards

LuckyTran · July 30, 2018, 16:32

Well if you have temperature errors then you shouldn't trust any result you get.

I think you can do this problem with only 1 cell zone, but somehow you ended up with two. Multiple cell zones are still doable, but then you need interfaces between them. Where are these interfaces? Or you can try merging all your cell zones so that you have only 1 cell zone (but still different boundaries).

Btw, I'm not sure where to apply the surface heat flux boundary condition in 2D (whether it is a heat flux boundary condition or a volumetric heat rate cell zone condition). You'll have to tinker a bit and figure out what works.

Sorabh · August 2, 2018, 02:39

I took an alternative approach, I split the domain by using facesplit, so now there are 2 faces, the smaller face, and the bigger domain. I apply volumetric heat generation to the smaller face and once again the results are not what I want them to be.

What is the correct way to simulate a continuous laser though?

July 27, 2018, 04:43	Simulating continuous laser at a point in a domain?	#1
Sorabh Member Saurabh Das Join Date: Jul 2018 Posts: 43 Rep Power: 8	Hello, I am trying to implement a scenario in Fluent where a continuous laser hits a point on a 5mm X 25mm tissue piece. I have applied this method: https://imgur.com/HBjiDE2 If you follow the aforementioned image, the laser will hit the small 0.1x0.1 mm square and the heat generated by the laser will then warm up the surrounding zone. That is the general idea. In order to do this, I made a 2D 5mmx25mm surface body in design modeller, followed by four points, and then a new line body from the four points, and finally a new surface body from the line body that I created. https://imgur.com/6BDy4ix (this image depicts the four points,lines and the resulting surface) On applying heat flux(a substitute for laser heating) on the surface body, the FLUENT results show that only that surface body is heated, and that the surrounding domain has not been affected at all. Is this approach correct? If yes, then what should I do to remedy the aforementioned scenario? Any help or advice will be highly appreciated. Thank you.

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July 27, 2018, 10:31		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	The surface heat flux idea to a small surface is correct. You just have to figure out what's wrong with your setup. Can you describe the rest of it? i.e. what the final mesh looks like, # cell zones, etc.

July 30, 2018, 00:44		#4
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	switch to TRANSIENT solver looks like you do not need any contacts here my opinion: to simulate laser welding heat source is applied in most cases, not the heat flux best regards

July 30, 2018, 16:32		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Well if you have temperature errors then you shouldn't trust any result you get. I think you can do this problem with only 1 cell zone, but somehow you ended up with two. Multiple cell zones are still doable, but then you need interfaces between them. Where are these interfaces? Or you can try merging all your cell zones so that you have only 1 cell zone (but still different boundaries). Btw, I'm not sure where to apply the surface heat flux boundary condition in 2D (whether it is a heat flux boundary condition or a volumetric heat rate cell zone condition). You'll have to tinker a bit and figure out what works.

August 2, 2018, 02:39		#6
Sorabh Member Saurabh Das Join Date: Jul 2018 Posts: 43 Rep Power: 8	I took an alternative approach, I split the domain by using facesplit, so now there are 2 faces, the smaller face, and the bigger domain. I apply volumetric heat generation to the smaller face and once again the results are not what I want them to be. What is the correct way to simulate a continuous laser though?