CHT Problem with moving solid part

MaxHeat · November 27, 2012, 11:31

Hi everybody,

I am currently doing my masters thesis about conjugate heat transfer in an annular gap with the inner cylinder rotating at a fairly high speed (10000 rpm, 630 rad/s). There is also a constant axial velocity assigned.
I want to investigate the temperature distribution in the rotor aswell as the heat transfer from the hot fluid to the rotor.
Since it's a CHT problem I meshed both, the fluid domain and the solid rotor. I attached a picture of the mesh used for my case with some more explanations: http://imageshack.us/photo/my-images/138/chtproblem.jpg

I modelled a 15 degree part and set pediodic boundary conditions at the side walls. I know that modelling only a cutout might be inappropriate for the problem since the solution for a Taylor-Couette-Flow with axial flow is like to be an assymetric one.

The more urgent problem is: I don't manage get the rotor-mesh to move.

Here is what I tried so far:
Declare the surfaces where the two meshes touch eachother as interfaces and set them to "coupled wall". I can't set the rotor-walls to "moving wall" since they are adjecent to a solid domain. So I tried to assign a rotational speed to the whole solid domain by selecting: cell zone conditions -> solid domain -> edit -> enable frame motion AND mesh motion -> select the rotational axis (X in this case) and my desired rotational speed.

But in the results file I see no rotation whatsoever, the annular gap acts as if both cylinders stand still.

Do I need to work with a dynamic mesh? Is my case even applicaple in Fluent?

Sorry for the long text, but I hope a precise question will produce precise answers

.

Regards,

Max

Karl · November 28, 2012, 04:06

Hallo Max,

in may opinion you don't need to set the solid as rotating zone. If you have access to the Ansys Customer Portal you can find the following answer.

"Unless you need to include the the convective term in the solid there is no need to set this as rotating. Though this is a common mistake that people make when setting up models.

As far as the calculation is concerned the walls of the solid are moving with the fluid but the conduction would occur the same way if
it is rotating or stationary.

An example where you would need to include the convective term would be
a billet of steel moving through a furnace where you have cumulative
heat build up along the direction of travel.

The manual reference that mentions this is provided below:

Section 10.2.2 of the user's guide.

"For solid zones, you only need to activate the Moving Reference Frame
option if you intend to include the convective terms in the energy
equation for the solid ( this equation (in the separate Theory
Guide)). Normally, this is not required if you wish to do a conjugate
heat transfer problem where the solid and fluid zones are moving"

November 27, 2012, 11:31	CHT Problem with moving solid part	#1
MaxHeat New Member Max Join Date: Nov 2012 Posts: 3 Rep Power: 14	Hi everybody, I am currently doing my masters thesis about conjugate heat transfer in an annular gap with the inner cylinder rotating at a fairly high speed (10000 rpm, 630 rad/s). There is also a constant axial velocity assigned. I want to investigate the temperature distribution in the rotor aswell as the heat transfer from the hot fluid to the rotor. Since it's a CHT problem I meshed both, the fluid domain and the solid rotor. I attached a picture of the mesh used for my case with some more explanations: http://imageshack.us/photo/my-images/138/chtproblem.jpg I modelled a 15 degree part and set pediodic boundary conditions at the side walls. I know that modelling only a cutout might be inappropriate for the problem since the solution for a Taylor-Couette-Flow with axial flow is like to be an assymetric one. The more urgent problem is: I don't manage get the rotor-mesh to move. Here is what I tried so far: Declare the surfaces where the two meshes touch eachother as interfaces and set them to "coupled wall". I can't set the rotor-walls to "moving wall" since they are adjecent to a solid domain. So I tried to assign a rotational speed to the whole solid domain by selecting: cell zone conditions -> solid domain -> edit -> enable frame motion AND mesh motion -> select the rotational axis (X in this case) and my desired rotational speed. But in the results file I see no rotation whatsoever, the annular gap acts as if both cylinders stand still. Do I need to work with a dynamic mesh? Is my case even applicaple in Fluent? Sorry for the long text, but I hope a precise question will produce precise answers . Regards, Max

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November 28, 2012, 04:06		#2
Karl New Member Karl Kargl Join Date: Mar 2009 Location: Austria Posts: 9 Rep Power: 17	Hallo Max, in may opinion you don't need to set the solid as rotating zone. If you have access to the Ansys Customer Portal you can find the following answer. "Unless you need to include the the convective term in the solid there is no need to set this as rotating. Though this is a common mistake that people make when setting up models. As far as the calculation is concerned the walls of the solid are moving with the fluid but the conduction would occur the same way if it is rotating or stationary. An example where you would need to include the convective term would be a billet of steel moving through a furnace where you have cumulative heat build up along the direction of travel. The manual reference that mentions this is provided below: Section 10.2.2 of the user's guide. "For solid zones, you only need to activate the Moving Reference Frame option if you intend to include the convective terms in the energy equation for the solid ( this equation (in the separate Theory Guide)). Normally, this is not required if you wish to do a conjugate heat transfer problem where the solid and fluid zones are moving"