Learning Forum

[Arijit Saha]

Hello everyone, hope everyone is doing fine and simulating well. I am here today with an issue related to radiation model which I just started getting my hands on. My problem statement is described as below:

I am trying to simulate an Urban Farming module with a 78 million cells and 44 million nodes. In the domain the Urban Farming module is surrounded by buildings and ground where shell conduction b.c is applied. The complication arrives when I switch to solar ray tracing model along with DO model used as the radiation model. Until initialization things are so far so good but when I try to run the simulation it gives an error " Divergence detected in DO intensity". But when I switch off the solar load or switch to Solar Irradiation model and run simply with the DO radiation it is running fine. So, now my doubt is what really is happening with the physics involved that it is running fine with Solar Irradiation model and not Solar Ray Tracing model? Or what is the absolute distinction between these two solar load model?

If anyone is aware or have any slightest idea about the proble please let me know, will be of great help.

Thank you 

[C N]

 

Hello ,

The Solar Ray Tracing Model

The solar load model’s ray tracing algorithm can be used to predict the direct illumination energy source that results from incident solar radiation. It takes a beam that is modelled using the sun position vector and illumination parameters, applies it to any or all wall or inlet/outlet boundary zones that you specify, performs a face-by-face shading analysis to determine well-defined shadows on all boundary faces and interior walls, and computes the heat flux on the boundary faces that results from the incident radiation. The solar ray tracing model includes only boundary zones that are adjacent to fluid zones in the ray tracing calculation. In other words, boundary zones that are attached to solid zones are ignored. The resulting heat flux that is computed by the solar ray tracing algorithm is coupled to the ANSYS FLUENT calculation via a source term in the energy equation.

DO Irradiation Model

The solar load model’s discrete ordinates (DO) irradiation option provides you with an easy means of applying a solar load directly to the DO model. Unlike the ray tracing solar load option, the DO irradiation method does not compute heat fluxes and apply them as heat sources to the energy equation. Instead, the irradiation flux is applied directly to semi-transparent walls (which you specify) as a boundary condition, and the radiative heat transfer is derived from the solution of the DO radiative transfer equation.

I hope now you would have understood the physics and the difference between the two models. Hope this helps you to solve your problem.

Thanks

 

 

 

[Arijit Saha]

Thanks for your reply but this is simply present in fluent manual I guess. I have tried to understand beforehand but didnt get it completely. If anyone can help in explaining it in simple terms will be of more help. Bdw, the model ran completely fine with 2019 fluent version but not with 2020 or 2021.

[C N]

Try changing the under relaxation factor and specific controls to avoid the divergence in DO intensity. In simple terms , check your boundary zones if attached to solid zones it will not take into account in solar ray tracing model. In ray tracing heat flux is calculated and in DO irradaition model irradaition flux is applied to walls. Hope this may help you . In latest version also you should get converged solution. 

Thanks

[Arijit Saha]

Much thanks for your reply and sorry for getting back so lately. By "In simple terms , check your boundary zones if attached to solid zones it will not take into account in solar ray tracing model" is not clear to me. Is it possible you can describe a little more?

[C N]

I mean some of the boundary conditions (wall areas assignd to solid region ) in solid cell zones like heat flux , temperature etc given will not be taken into consideration in ray tracing model for radiation transfer calculation . also to avoid divergence error. Go to operating controls - changing the scaling factor of momentum , energy equation . Under relaxation factors. 

[Arijit Saha]

Hi C N, I have been trying constantly to reach to a solution but still not succesful in that regard. Somehow while initializing I am getting this warning -

The neighboring cell thread 865403 of semi-transparent wall zone 129 is non-fluid.

In the solar load model, boundary zones adjacent to non-fluids are not included in the ray tracing algorithm.

The solution will proceed however results might not be as expected.

Just wondering does this warning have any crucial role in leading the solution to 'floating point error'?

[Arijit Saha]

Also to add, this error is only appearing when I am assigning the boundary condition in radiation setup as semi-transparent. Will be really helpful if you can suggest a possible way out.

Thank you