CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   CFX (https://www.cfd-online.com/Forums/cfx/)
-   -   CFX domain comparison (https://www.cfd-online.com/Forums/cfx/86782-cfx-domain-comparison.html)

 Kiat110616 April 1, 2011 15:08

CFX domain comparison

2 Attachment(s)
Dear All,

I'm a little confused about different domain condition.
First case study, I created the only one fluid model.

Domain Settings
- Domain Type @ Fluid domain
- Reference pressure @ 1 atm
- Domain motion @ stationary
- Mesh Deformation @ regions of motion specified

Boundary Condition
- Total pressure at an inlet surface
- Mass flow rate at an outlet surface
- Runner surface is set up with a angular velocity
- Other surface is set up to stationary wall (no slip wall)

Attachment 7127

Second case study, I created the two fluid models. I have separated the model into two domains is stationary and rotating domain.

First domain settings
- Domain Type @ Fluid domain
- Reference pressure @ 1 atm
- Domain motion @ stationary

Second domain settings
- Domain Type @ Fluid domain
- Reference pressure @ 1 atm
- Domain motion @ rotating along Z axis

Interface settings
- Interface models @ general connection
- Frame change @ Frozen rotor
- Pitch change @ none

Boundary Condition
- Total pressure at an inlet surface @ stationary domain
- Mass flow rate at an outlet surface @ rotating domain
- Other surface is set up to wall condition (no slip wall)

Attachment 7128

The results of both case studies are different. The total pressure different between inlet and outlet of the first case is 71 kPa and second case is 54 kPa. Also, the hydraulic efficiency of both case studies is different. It is important to determine which case study is accurate. Any feedback is greatly appreciated.

 ghorrocks April 3, 2011 06:52

I do not understand what the difference between the two simulations is. Also I do not understand what output is different. You will have to explain it more.

 Kiat110616 April 3, 2011 10:18

The both case studies, same boundary conditions: the total pressure at inlet and mass flow rate are applied at output but the fluid volume is different. The first case was created with only one of fluid volume domain. The second case was separated into two fluid volume domains. The results from these cases are different. The different total pressure at inlet and outlet are affected with the hydraulic efficiency.

I want to know, which case study is suitable for analyzing this problem. Thank you for your respond.

 ghorrocks April 3, 2011 19:00

But don't you have a rotor and a stator? In this case the only valid approach is to put the rotor in a rotating frame of reference and the stator in a staionary one, so the 2 domain approach is the only choice.

If you have only one domain then either everything is still or everything is rotating. That does not sound right to me.

 Kiat110616 April 3, 2011 22:43

Ghorrocks

Quote:
 Originally Posted by ghorrocks (Post 302052) But don't you have a rotor and a stator? In this case the only valid approach is to put the rotor in a rotating frame of reference and the stator in a staionary one, so the 2 domain approach is the only choice. If you have only one domain then either everything is still or everything is rotating. That does not sound right to me.