What conditions should be given to a coupled wall in ansys fluent?

cfdquery · November 14, 2018, 11:59

I am trying to model a trapezoidal cavity receiver and trying to find the heat losses from it.
The inner part of the trapezium has 3 walls with air on one side and insulation on the other. In the boundary conditions dialog box of fluent solver i have given the boundary condition for the wall as heat flux condition. what should i put as the boundary condition for its shadow?
I tried giving the shadow the same conditions as the wall but it results in the area in the insulation to reach ridiculous temperatures of 5000k.

LuckyTran · November 14, 2018, 14:37

If you have a wall and shadow-wall then that means it's an interface. It should be a coupled wall (both of them) and neither of them should have a boundary condition.

Can you post a sketch of your domain? Is it a wall that needs a BC or is it an interface between two cell zones?

cfdquery · November 14, 2018, 14:59

the inner walls(horizontal and incline walls) are the receivers of my geometry. They receive solar flux from mirrors. The bottom edge is a glass cover to keep the air inside. The inner region is air and on the other side is insulating material. what should the boundary condition be for incident heat flux on the receivers?

LuckyTran · November 14, 2018, 15:32

coupled walls don't have boundary conditions, they are not boundaries. There is an option in Fluent that allows you to impose a temperature, heat flux, etc. on a coupled wall, but that is a feature for you to constrain the problem in non-physical ways.

cfdquery · November 15, 2018, 00:00

Any idea on how i should impose the boundary conditions in my case. If i give 0 heat flux to the shadow it behaves as a adiabatic wall and if it the same heat flux conditions as the wall is given to the shadow the temperature will be very high.

November 14, 2018, 11:59	What conditions should be given to a coupled wall in ansys fluent?	#1
cfdquery New Member Join Date: Nov 2018 Posts: 3 Rep Power: 8	I am trying to model a trapezoidal cavity receiver and trying to find the heat losses from it. The inner part of the trapezium has 3 walls with air on one side and insulation on the other. In the boundary conditions dialog box of fluent solver i have given the boundary condition for the wall as heat flux condition. what should i put as the boundary condition for its shadow? I tried giving the shadow the same conditions as the wall but it results in the area in the insulation to reach ridiculous temperatures of 5000k.

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November 14, 2018, 14:37		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	If you have a wall and shadow-wall then that means it's an interface. It should be a coupled wall (both of them) and neither of them should have a boundary condition. Can you post a sketch of your domain? Is it a wall that needs a BC or is it an interface between two cell zones?

November 14, 2018, 15:32		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	coupled walls don't have boundary conditions, they are not boundaries. There is an option in Fluent that allows you to impose a temperature, heat flux, etc. on a coupled wall, but that is a feature for you to constrain the problem in non-physical ways.

November 15, 2018, 00:00		#5
cfdquery New Member Join Date: Nov 2018 Posts: 3 Rep Power: 8	Any idea on how i should impose the boundary conditions in my case. If i give 0 heat flux to the shadow it behaves as a adiabatic wall and if it the same heat flux conditions as the wall is given to the shadow the temperature will be very high.