Learning Forum

[teguhhady]

Dear all  
I simulate flow in curved pipe in FLUENT 17.2. The velocity contour is good but streamline and velocity vectors are not good. It should be same as sample secondary flow in pipe elbow.
 
Do you have any suggestion about my result?
 
Thank you

[Rob]

Please can you post the images into the message: as staff we can't download attachments. Also label the "not good" bits!

[teguhhady]

[teguhhady]

I am sorry that the figure is not attached. Here, I post the pictures. 

The velocity magnitude contour is ok. The left side of pipe is outer side of spiral coil. I see the velocity vectors and streamline are not like the bottom picture. I the axial velocity contribute this. I think to capture the secondary flow i should only use radial and tangential velocity. But, I dont know how to choose the axis because my case is spiral pipe.

Thank you for your help

Teguh

[Keyur Kanade]

are these images at the same section?

is your flow converged?

can you please insert you inlet & outlet conditions images 

[teguhhady]

dear kkanade, 

 

Thank you for your reply. yes, all of them in the same location (downstream of coils). The flow is also converged. I am using inflation on the wall. My inlet is velocity inlet and outlet is outflow.

Thank you for your help

[Keyur Kanade]

can you please check by using pressure outlet. 

[Rob]

Change the vector options to "in plane". That will show the flow as per the section on your images. 

[teguhhady]

Dear rwoolhou

 

Thank you for your reply. The picture of velocity vector I display in the previous post is already using vector option "in plane".  I still do not know why velocity vector and streamline are not good. I have tried some ways but it does not work

 

thank you for your help

[teguhhady]

Dear kkanade

 

Before doing spiral case, I have tried straight ribbed tube to generate the secondary flow. secondary flow velocity vector and streamline are acceptable by using outflow boundary condition. So, I thought it was ok to use outflow BC. I will try pressure outlet.

Thank you for your help

[Rob]

Can you show why you'd expect to get flow like in the diagram? Flow around tight bends tends to generate swirl, I'd not expect two symmetrical flows unless there's something else going on. 

[teguhhady]

Dear rwoolhou

Thank you for your reply. Well, Actually I am thinking about there is something happens. I was thinking that this is torsional effect of the coil but my supervisor does not agree with my reason. I see a paper "Numerical investigation of heat transfer and entropy generation of laminar flow in helical tubes with various cross sections" (I attach the result of their simulation). There is clear explanation about that. The paper also presents the secondary flow of the coil tube velocity contour and velocity vectors also same as mine. My supervisor tells me that my result is not correct. I am still trying to find how this happens.

 

Thank you so much for your help

[Rob]

Is your model single phase and laminar?  Assuming there is an inflation layer and y+ is about 1 (or less that 5) and you've done a mesh refinement study then I'd suggest your CFD result is correct. The bulk flow above looks sensible, I'm unsure of the secondary flow without running the model (and I'm not going to do that!). What does your supervisor think is going on? 

As staff we're somewhat limited in how much engineering help we can offer as this is a public forum. In this case I don't know what the exact flow will be which avoids that issue! 

[teguhhady]

Dear rwoolhou

 

Thank you for your assistance. I am modeling single phase, laminar and turbulent flow. I do the inflation layer and my y+ is 1. I am still looking for the r5eason. Finnally, I find a paper which has same case and same streamline as mine. 

I post the link if any other people have the same case as mine.

https://journals.sagepub.com/doi/pdf/10.1177/1687814017700059

Thanks you so much for your help.

Best regards