Local cylindrical coordinate system

dniem · July 9, 2018, 11:55

Hello, I hope, someone can help me.
I have a problem setting boundary conditions in a combustion simulation.
I try to simulate a combustion chamber with 8 inlets. I use velocity inlets and constant values for velocity components:

Radial-Velocity: 3.67 m/s
Tangential-Velocity: 3.72 m/s
Axial-Velocity: 7.42 m/s

I have set local cylindrical coordinate systems for each inlet, using coordinates derived from the mesh in ICEM.
In the first picture you can see the local axis of one inlet. I have used a line surface using the points "Axis Origin" and "Axis Direction" from the boundary conditions of one inlet, to check the axis. It is perfectly rectangular to the inlet surface.
In the second picture you can see the vectors of velocity magnitude. They are all going to the wrong direction. It seems that there is a mistake with the axis, but I cannot find it.
I changed the setting for Rotation-Axis Direction in the cell zone conditions from 0-1-0 to 1-0-0 or 0-0-1, but this didnt solve the problem.
If anyone knows a solution, please help me.
Rotation_Axis.jpg

Velocity_Vectors_Inlets.jpg

LuckyTran · July 9, 2018, 12:54

What seems wrong with your velocity vectors? They look somewhat right to me. Which direction do you want them to go at? You specify a radial and tangential velocity so of course they will point away from the local centers.

Rotation-axis is used to specify the coordinate system for the Fluent global variable Radial/Axial/Tangential velocity.

You should use the axis origin and axis direction in the velocity inlet tab. But you won't be able to visualize these in Fluent using radial/axial/tangential velocity variable names because those are attached to the rotation-axis and rotation-origin in the cell zone conditions.

dniem · July 9, 2018, 13:43

Thank you for your answer lucky tran.
The velocity vectors should form a swirling flow. I want to model swirl stabilized flames. So the vectors should be symmetric to the axis shown in the first picture.
I have used the axis origin and axis direction in the velocity inlet tab as you recommended.

July 9, 2018, 11:55	Local cylindrical coordinate system	#1
dniem New Member Join Date: Jul 2018 Posts: 2 Rep Power: 0	Hello, I hope, someone can help me. I have a problem setting boundary conditions in a combustion simulation. I try to simulate a combustion chamber with 8 inlets. I use velocity inlets and constant values for velocity components: Radial-Velocity: 3.67 m/s Tangential-Velocity: 3.72 m/s Axial-Velocity: 7.42 m/s I have set local cylindrical coordinate systems for each inlet, using coordinates derived from the mesh in ICEM. In the first picture you can see the local axis of one inlet. I have used a line surface using the points "Axis Origin" and "Axis Direction" from the boundary conditions of one inlet, to check the axis. It is perfectly rectangular to the inlet surface. In the second picture you can see the vectors of velocity magnitude. They are all going to the wrong direction. It seems that there is a mistake with the axis, but I cannot find it. I changed the setting for Rotation-Axis Direction in the cell zone conditions from 0-1-0 to 1-0-0 or 0-0-1, but this didnt solve the problem. If anyone knows a solution, please help me. Rotation_Axis.jpg Velocity_Vectors_Inlets.jpg

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July 9, 2018, 12:54		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,756 Rep Power: 66	What seems wrong with your velocity vectors? They look somewhat right to me. Which direction do you want them to go at? You specify a radial and tangential velocity so of course they will point away from the local centers. Rotation-axis is used to specify the coordinate system for the Fluent global variable Radial/Axial/Tangential velocity. You should use the axis origin and axis direction in the velocity inlet tab. But you won't be able to visualize these in Fluent using radial/axial/tangential velocity variable names because those are attached to the rotation-axis and rotation-origin in the cell zone conditions.

July 9, 2018, 13:43		#3
dniem New Member Join Date: Jul 2018 Posts: 2 Rep Power: 0	Thank you for your answer lucky tran. The velocity vectors should form a swirling flow. I want to model swirl stabilized flames. So the vectors should be symmetric to the axis shown in the first picture. I have used the axis origin and axis direction in the velocity inlet tab as you recommended.