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How to simulate surface roughness in CFD simulation?

Posted Feb 14, 2019, 3:30 a.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD), Heat Transfer Version 5.4 3 Replies

H. LI
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Dear Mr./Miss.,

We manufactured a liquid cooled heat sink by 3DP, and we intend to experimentally and numerically study the thermal and flow performances of the heat sink. The problem is that the roughness of cooling channel surface is not perfectly smooth due to the uncertainty during 3DP process. Therefore, is it possible to use any boundary condition setup to simulate such kind of rough surface in CFD simulation?

Kind regards, Hao LI

3 Replies Last Post May 31, 2019, 11:31 a.m. EDT
Michael Rembe Certified Consultant
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Posted: 6 years ago Feb 14, 2019, 10:04 a.m. EST

Hi Hao,

the two equation turbulence models of COMSOL provide wall functions for rough walls. You can find it in the COMSOL documentation (for example: Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model).

Best regards

Michael

-------------------
Michael Rembe
Rembe Consulting PartG mbB
www.rembe-consulting.de


Hi Hao, the two equation turbulence models of COMSOL provide wall functions for rough walls. You can find it in the COMSOL documentation (for example: Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model). Best regards Michael
H. LI
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Posted: 6 years ago Feb 15, 2019, 2:55 a.m. EST
Updated: 6 years ago Feb 15, 2019, 2:55 a.m. EST

Hi Hao,

the two equation turbulence models of COMSOL provide wall functions for rough walls. You can find it in the COMSOL documentation (for example: Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model).

Best regards

Michael

Thanks very much Michael.

>Hi Hao, > >the two equation turbulence models of COMSOL provide wall functions for rough walls. You can find it in the COMSOL documentation (for example: Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model). > >Best regards > >Michael Thanks very much Michael.
Cameron Parvini
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Posted: 6 years ago May 31, 2019, 11:31 a.m. EDT
Updated: 6 years ago May 31, 2019, 11:32 a.m. EDT

Hello All,

Sorry to revive the topic after it appears to have been resolved, but I have a similar lack of understanding.

I'm attempting to implement a given roughness height in my k- turbulent flow models of hydrazine and xenon.

I've read through the documentation and it sounds like there should be a location in the standard COMSOL GUI to insert or modify the value of to account for varying wall roughnesses---the documentation specifies that modifying and is the appropriate way to adjust for different sand roughness heights.

I cannot seem to find a means to insert the appropriate node under the Wall boundary condition, or introduce an appropriate choice in the turbulent model settings, such that the roughness height is available for me to modify. The back-end equations view shows no such value or in the Wall node.

Is there a way to activate such that I can easily modify it, or are we supposed to manually modify the friction roughness equation according to the theory provided in Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model?

I appreciate your time, thank you!

Hello All, Sorry to revive the topic after it appears to have been resolved, but I have a similar lack of understanding. I'm attempting to implement a given roughness height k_s in my k-\epsilon turbulent flow models of hydrazine and xenon. I've read through the documentation and it *sounds* like there should be a location in the standard COMSOL GUI to insert or modify the value of k_s to account for varying wall roughnesses---the documentation specifies that modifying C_s and k_s is the appropriate way to adjust for different sand roughness heights. I cannot seem to find a means to insert the appropriate node under the Wall boundary condition, or introduce an appropriate choice in the turbulent model settings, such that the roughness height is available for me to modify. The back-end equations view shows no such value k_s or C_s in the Wall node. Is there a way to activate k_s such that I can easily modify it, or are we supposed to manually modify the friction roughness equation u_\tau according to the theory provided in Theory for the Turbulent Flow Interfaces -> The k-ε Turbulence Model? I appreciate your time, thank you!

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