[CFD] How does the Surface-to-Surface (S2S) Radiation Model Work?

[@shaunbentley8844]

First of all, I love your videos. I’m glad you take the time to really get into the weeds on important CFD topics. Slight inaccuracy at 2 minutes. Radiation does not scale with the fourth power of the temperature difference. It scales with the difference of the fourth power temperatures. Appreciating this difference in understanding means that you may consider radiation to be significant when temperature differences are still relatively small, but the absolute temperatures are large.

[@fluidmechanics101]

Amazing, thanks for the clarification. I have pinned the comment so everyone can see

[@谢岸峰-z4l]

Thank you Aidan, this video is very useful while trying to figure out the mechanism of the radiation model in Ansys Fluent.

[@karthikvigneshwar8742]

Very clear and concise explanation ! Thank you !!

[@shadabmohammed3115]

Thank you so much for the detailed explanation !!!👍

[@saianirudhkarumuri9779]

Amazing explanation, thank you so much !

[@wehavebiscuits]

You're a lifesaver dude

[@Lunamycat34]

Great video, Adian. What does internal emissivity and external emissivity mean in Fluent S2S radiation model? Thanks

[@fluidmechanics101]

Good question. I'd have to look this up in the user manual

[@vidyadharkarlapalem5824]

Hi. Its a nice video. It is mentioned that after calculating radiation heat fluxes from radiosity matrix equation, they are applied to the CFD energy equation as a boundary condition. Is it like convection flux at the wall= conduction flux at the wall + net radiation flux at the wall. How it will be implemented in Fluent. Is it taken care automatically when we select the wall as a participating surface in S2S model and provide emissivity values. Or is it done through any volumetric radiation source terms? Request you to kindly explain me this. Thanks.

[@fluidmechanics101]

Good question. I hesitate to answer because only ANSYS will know exactly how the boundary condition is applied. My guess is that it is accounted for automatically in the boundary condition (your first answer) rather than a volumetric source but that is my best guess 😅

[@vidyadharkarlapalem5824]

@@fluidmechanics101 Hi. Thanks for the reply. On the ASNYS Learning Forum, they replied to this question saying the radiation flux is applied as a source term in the energy equation. I have referred the user manual of COMSOL Multiphysics. They have also mentioned that the radiation flux is applied as an internal source term. I think they have applied the source term as divergence of radiation flux at the surfaces. I don't know if they have followed similar procedure given in section 4.2-6 Boundary conditions (Chapter on Heat Conduction) in Numerical heat transfer and fluid flow written by Patankar. Since we specify emissivity value at the participating surfaces, the source term would be applied only at the surfaces. Request you to kindly give your comments about this. Thanks.

[@SamarSinghal]

sir can you make video on ansys fluent or explain ray tracing method. it would be really helpful. thanks in advance.

[@siddharthaug10]

Hey, thanks a lot for explanation. one correction here, Kirchhoff's law does not state that absorptivity = emissivity for all the cases. its only for a very specific case. Is there a way to change the value of absorptivity in ANSYS Fluent if possible?

[@fluidmechanics101]

🤔 probably ... i think you will probably need to use a UDF

[@siddharthaug10]

Fluid Mechanics 101 could you please point me out to the right direction to write a UDF in Fluent?

[@erinsam7821]

@@siddharthaug10 You have probably found the answer to your question already, but for anyone else, Fluent has a seperate guide known as 'ANSYS Fluent UDF Manual'. Read the first few chapters and you'll obtain a general idea of writing UDFs. UDFs must be written and stored in the same directory that the Fluent Case files are located. There is a method of compiling the UDFs to create a UDF library from within Fluent itself (if I'm not mistaken, in older versions, it had to compiled by the user externally). Then the User-Defined Functions can be selected when selecting modeling parameters. This is only a rough outline and there is more to it than this process.

[@fluidmechanics101]

Thanks Erin, I am sure this will be useful to a lot of people who are new to Fluent

[@tejaskulkarni8639]

Brilliant! Thank you !

[@rafaortwein6646]

Nice explanation

[@alb8350]

Hi Very interesting video but I have a question How can I running long transient simulation with solar ray tracing? Regards

[@LokalTraveller]

Wonderful explanation sir. Can you please share transcripts of all your lectures?

[@fluidmechanics101]

You can get all the slides from my website

[@barsisklar5783]

Can I use this model if one of my body is transparent like glass?

[@fluidmechanics101]

Good question. Glass is quite refractive so I think you would probably need DO. Maybe drop ANSYS a quick email to ask?

[@rjw678]

Next time Maybe I can awake and listen carefully. I will listen this again snd again.

[@antanas9015]

Radiation is a surface phenomenon only in the case of a non-participating medium, i.e. when optical thickness of a medium = 0, or am i wrong?

[@SugusRedondo]

I think you are right. There is also volume radiation. it's not only a surface phenomena

[@fluidmechanics101]

Yes, correct!

[@Bx7o]

Great job thx, plz if you can explain these model of radiation (Discrete Ordinates (DO))

[@fluidmechanics101]

Hi Ayham, great im glad you found it useful! DO will be next, i just thought i would cover S2S first as it is most popular :)

[@pavansinghyadav9975]

Bro is doing the crime by providin such a great content for free, that is why Police is looking for him😛

[@rahulwadibhasme2119]

Hello thanks this is very useful, can you please make video on DOM and Montecarlo radiation. Thanks

[@fluidmechanics101]

Yep, DOM will be coming soon 😊

[@mohamednabil5149]

Thank you Aiden, Nice explanation 👍 you have any video explaining about MC radiation model?

[@fluidmechanics101]

Not yet 😞 working on it!

[@ichlasalpurqon7820]

awesome. cau u explain about weighted sum gray gases model (WSGGM)?

[@alexanderdanilin9510]

Thank you for the video. Do you know the models describing the radiative heat transfer inside the gas medium?

[@fluidmechanics101]

I havent looked into these models yet, as they arent as popular in most CFD applications but they are definitely something i will be looking into in the future!

[@Bx7o]

and Monte Carlo plz

[@jhkeum0124]

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