Has the kind of mesh influence on the solving method used by software?

fshak92 · March 12, 2012, 10:07

1) In a conjugate heat transfer case for finding the HTC and LocalHTC I've meshed my model(a body surrounded by air) in two ways(first polyhedral and second Trimmer).
There isn't any velocity and i've used the segregated solver and all the conditions are same for both cases.
In trimmer case Just the energy equation is solved but for polyhedral, the momentum and continuity equations are solved as well.
I wonder if someone tells me how the kind of mesh influences on solving equations in my case.

2)And also do you know how Heat transfer coefficient and LocalHTC are calculated by the software? the tutorial hasn't explained in a good way.

Thank you in advance.

siara817 · March 13, 2012, 12:35

How was the quality of the mesh for the both cases?
If the quality of the mesh is low in any case, then the solution will not converge.
I hope you know how to check for example Cell quality in STAR CCM.
Good luck

MFitl · March 14, 2012, 02:07

Quote:

Originally Posted by omid88

1)

2)And also do you know how Heat transfer coefficient and LocalHTC are calculated by the software? the tutorial hasn't explained in a good way.

The definition of the HTC is:

$\alpha$ = $\frac{\Delta T}{\Delta Q} = \frac{T - T_{ref}}{\Delta Q}$

Depending on $T_{ref}$ the $\alpha$ is different for the same $\Delta Q$ .

For the HTC $T_{ref}$ is the temperature you need to set in Tools|FieldFunctions|Heat Transfer Coefficient.

For the LocalHTC $T_{ref}$ is the local temperature of the cell next to the wall.

abdul099 · March 15, 2012, 03:27

The solver should do the same for both meshes. Can you create a summary report on both cases and compare them for different settings (apart from mesh settings)?

fshak92 · March 15, 2012, 07:02

Thank you all for your answers

To Abdul099 : Firstly i set some constant temperature on the body as a heat source and let the wall be adiabatic(i know its not realistic) and the above mentioned problem was occured. but after setting some constant temperature to the wall , both of poly and trimmer behave in a same way and just an energy eqation is solved(not Momentum and Continuity).I dont know why in first case the difference in solution method was seen...

To Siara817: Thank you for your explanation but i cannot understand exactly the meaning of 'the local temperature of the cell next to the wall'. Because in spite of same reference temperature with the wall temperature,,the LHTCs are 1000times more than HTCs.

Again Thank you all for your considerations.

March 12, 2012, 10:07	Has the kind of mesh influence on the solving method used by software?	#1
fshak92 Senior Member Join Date: Dec 2011 Posts: 121 Rep Power: 14	1) In a conjugate heat transfer case for finding the HTC and LocalHTC I've meshed my model(a body surrounded by air) in two ways(first polyhedral and second Trimmer). There isn't any velocity and i've used the segregated solver and all the conditions are same for both cases. In trimmer case Just the energy equation is solved but for polyhedral, the momentum and continuity equations are solved as well. I wonder if someone tells me how the kind of mesh influences on solving equations in my case. 2)And also do you know how Heat transfer coefficient and LocalHTC are calculated by the software? the tutorial hasn't explained in a good way. Thank you in advance.

March 13, 2012, 12:35		#2
siara817 Senior Member siamak rahimi ardkapan Join Date: Jul 2010 Location: Copenhagen, Denmark Posts: 220 Rep Power: 17	How was the quality of the mesh for the both cases? If the quality of the mesh is low in any case, then the solution will not converge. I hope you know how to check for example Cell quality in STAR CCM. Good luck fshak92 likes this.

March 15, 2012, 03:27		#4
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 21	The solver should do the same for both meshes. Can you create a summary report on both cases and compare them for different settings (apart from mesh settings)? fshak92 likes this.

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March 15, 2012, 07:02		#5
fshak92 Senior Member Join Date: Dec 2011 Posts: 121 Rep Power: 14	Thank you all for your answers To Abdul099 : Firstly i set some constant temperature on the body as a heat source and let the wall be adiabatic(i know its not realistic) and the above mentioned problem was occured. but after setting some constant temperature to the wall , both of poly and trimmer behave in a same way and just an energy eqation is solved(not Momentum and Continuity).I dont know why in first case the difference in solution method was seen... To Siara817: Thank you for your explanation but i cannot understand exactly the meaning of 'the local temperature of the cell next to the wall'. Because in spite of same reference temperature with the wall temperature,,the LHTCs are 1000times more than HTCs. Again Thank you all for your considerations.