Fluctuations in Forces in OpenFOAM

joana0 · June 15, 2023, 09:31

Hello.

I'm running a simulation of a funnel, in a cylindrical domain, using RANS in combination with κ-ω SST model.

After developing several meshes using ANSA, due to problems with high yPlus values, I've managed to get good values, and converging residuals.

The only thing that's not according to my expectations is the forces I'm getting. I used a python script to calculate these, and attached are the forces vs Iteration.

Is this acceptable? Considering there's some recirculation and separation of the flow, some fluctuations are expected, but I believe this is not the case. I've also attached my residuals.

https://ulisboa-my.sharepoint.com/:f...eaJIg?e=jWdkA5

Magistrane · June 16, 2023, 03:06

Hello Joana,

It's difficult to answer your question without more details. Could you be more precise about your simulation and include some screenshots ?

Nevertheless, you are using a dynamic model, the variations are not shocking to me. For Fx for example, the variation is "only" 3%. Also, forces in the y and z directions seems very weak compared to Fx. Also, what is the time step of the plots ? Have you investigated the pressure field on your structure to try to understand the origin of this variation ?

What do you mean by : "developing several meshes using ANSA". Is it a mesh convergence study ?

Hope I can help,

Have a good day

June 15, 2023, 09:31	Fluctuations in Forces in OpenFOAM	#1
joana0 New Member Joana Viegas Join Date: Jun 2023 Posts: 1 Rep Power: 0	Hello. I'm running a simulation of a funnel, in a cylindrical domain, using RANS in combination with κ-ω SST model. After developing several meshes using ANSA, due to problems with high yPlus values, I've managed to get good values, and converging residuals. The only thing that's not according to my expectations is the forces I'm getting. I used a python script to calculate these, and attached are the forces vs Iteration. Is this acceptable? Considering there's some recirculation and separation of the flow, some fluctuations are expected, but I believe this is not the case. I've also attached my residuals. https://ulisboa-my.sharepoint.com/:f...eaJIg?e=jWdkA5

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June 16, 2023, 03:06		#2
Magistrane Member Ilan Join Date: Dec 2018 Posts: 52 Rep Power: 7	Hello Joana, It's difficult to answer your question without more details. Could you be more precise about your simulation and include some screenshots ? Nevertheless, you are using a dynamic model, the variations are not shocking to me. For Fx for example, the variation is "only" 3%. Also, forces in the y and z directions seems very weak compared to Fx. Also, what is the time step of the plots ? Have you investigated the pressure field on your structure to try to understand the origin of this variation ? What do you mean by : "developing several meshes using ANSA". Is it a mesh convergence study ? Hope I can help, Have a good day