Heat generation due to viscosity/wall friction

Altosmos · March 25, 2023, 09:52

Hey everyone,

I doing a sensitivity analysis in turbomachinery by changing the wall roughness. I also have static wall temperatures defined as boundary conditions. I would like to calculate the heat generation (in Watts) generated due to friction and compare it to the heat flux through conduction in CFX-Post.

How can I build the relation for the heat generation due to viscosity?

Thanks in advance and have a nice day

(Any literature would also be highly appreciated)

Gert-Jan · March 25, 2023, 11:04

Shouldn't you just select the item "Viscous work' in CFX-Pre?

Altosmos · March 26, 2023, 11:19

Hi,

I do enable the viscous work option but that only makes the software account for it. I also want to qualitatively calculate the heat generated by friction. Herefore, I probably need the right equation to convert the shear stress force to power or dissipation.

ghorrocks · March 26, 2023, 18:58

It might be easier to do one simulation with viscous work option activated and another simulation with it turned off. Then you can compare the results. And in CFD-Post there is a difference option which gives you the difference between two simulations which might be useful.

Altosmos · March 26, 2023, 19:31

Thank you for your answer but that might not be a reliable way for my case since I also have conduction heating and the lack of viscous work may increase the heat flux through conduction and degenerate the results.

ghorrocks · March 26, 2023, 21:03

It depends on exactly what you are trying to do. If you want to know what difference the viscous work makes then my suggestion works well. If you want to know how much heating power is coming from viscous heating then you need a different approach.

The viscous work term is discussed in the CFX Theory Manual, in equation 1-86. Note that it is not a "shear stress force" effect as your last post suggested but a stress tensor and velocity vector effect.

Altosmos · March 27, 2023, 06:22

Yeah, I am trying to calculate how much heating power is coming from viscous heating and looking for a way.

Thanks, I will check the Theory Manual and see if I can find a way.

Opaque · March 27, 2023, 12:41

http://www.owlnet.rice.edu/~ceng501/Chap6.pdf

March 25, 2023, 09:52	Heat generation due to viscosity/wall friction	#1
Altosmos New Member Altay Join Date: Nov 2019 Posts: 6 Rep Power: 7	Hey everyone, I doing a sensitivity analysis in turbomachinery by changing the wall roughness. I also have static wall temperatures defined as boundary conditions. I would like to calculate the heat generation (in Watts) generated due to friction and compare it to the heat flux through conduction in CFX-Post. How can I build the relation for the heat generation due to viscosity? Thanks in advance and have a nice day (Any literature would also be highly appreciated)

March 26, 2023, 18:58		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	It might be easier to do one simulation with viscous work option activated and another simulation with it turned off. Then you can compare the results. And in CFD-Post there is a difference option which gives you the difference between two simulations which might be useful. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 26, 2023, 21:03		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	It depends on exactly what you are trying to do. If you want to know what difference the viscous work makes then my suggestion works well. If you want to know how much heating power is coming from viscous heating then you need a different approach. The viscous work term is discussed in the CFX Theory Manual, in equation 1-86. Note that it is not a "shear stress force" effect as your last post suggested but a stress tensor and velocity vector effect. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 27, 2023, 12:41		#8
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	http://www.owlnet.rice.edu/~ceng501/Chap6.pdf __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 25, 2023, 11:04		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	Shouldn't you just select the item "Viscous work' in CFX-Pre?

March 26, 2023, 11:19		#3
Altosmos New Member Altay Join Date: Nov 2019 Posts: 6 Rep Power: 7	Hi, I do enable the viscous work option but that only makes the software account for it. I also want to qualitatively calculate the heat generated by friction. Herefore, I probably need the right equation to convert the shear stress force to power or dissipation.

March 26, 2023, 19:31		#5
Altosmos New Member Altay Join Date: Nov 2019 Posts: 6 Rep Power: 7	Thank you for your answer but that might not be a reliable way for my case since I also have conduction heating and the lack of viscous work may increase the heat flux through conduction and degenerate the results.

March 27, 2023, 06:22		#7
Altosmos New Member Altay Join Date: Nov 2019 Posts: 6 Rep Power: 7	Yeah, I am trying to calculate how much heating power is coming from viscous heating and looking for a way. Thanks, I will check the Theory Manual and see if I can find a way.