Pulsatile Inlet & Opening Outlet

zxcvbnm2010 · April 8, 2015, 03:19

Hi everyone

I have a trouble. I run model as a straight tube. When I set the pulsatile inlet and constant pressure outlet, it will be overflow.
So, I change the constant pressure outlet to opening outlet. But the results are really strange. The flow is reverse. How could I get the normal flow direction(In→Out) at any timestep?

Thanks a lot for your help and time.
Best Regards

0.png

1.jpg

2.jpg

ghorrocks · April 8, 2015, 05:52

In the post processor draw a contour of the normal component of velocity on the boundary. Then use it to draw a contour of velocity =0. All the flow in one direction will be one colour, all the flow in the opposite direction will be another colour.

zxcvbnm2010 · April 8, 2015, 08:16

Quote:

Originally Posted by ghorrocks

In the post processor draw a contour of the normal component of velocity on the boundary. Then use it to draw a contour of velocity =0. All the flow in one direction will be one colour, all the flow in the opposite direction will be another colour.

Sorry, you misunderstood what I meant. My problem is how to solve the flow direction correct (In→Out)?
At some timestep result, the flow direction is wrong (Out→In).
Thank you.

ghorrocks · April 8, 2015, 17:54

If you mean the backflow is wrong, so how to stop the back flow? Well, the backflow is a result of the conditions you apply. If you are applying a pulsing flow then it sounds like backflow is inevitable.

I think you need to go back to basics on this simulation. What are you actually trying to model? What do you know about the flow?

zxcvbnm2010 · April 8, 2015, 22:13

Quote:

Originally Posted by ghorrocks

If you mean the backflow is wrong, so how to stop the back flow? Well, the backflow is a result of the conditions you apply. If you are applying a pulsing flow then it sounds like backflow is inevitable.

I think you need to go back to basics on this simulation. What are you actually trying to model? What do you know about the flow?

Sorry, I know backflow is inevitable. But as you could see the picture, my inlet is change into outlet.

I want to try a pulsatile flow in a stright tube. I setup inlet boundary conditions as a function of timestep. Inlet is always be inlet, but this picture result inlet flow direction is oppsite. I need to get inlet flow direction is a fixed direction, how could I solve this problem.

Thank you in advance.

zxcvbnm2010 · April 9, 2015, 02:01

I think I found the problem. Is my expression too complex?

Plot it.

I really need this wave of inlet velocity. If my expression is incorrect, please help me.

Many thanks.

ghorrocks · April 9, 2015, 06:08

Can you post your CCL?

FrankW · April 9, 2015, 08:40

Why do you use Current Time Step (ctstep) instead of time (t)?

zxcvbnm2010 · April 9, 2015, 09:31

I misunderstand ctstep mean...
Thank you all. I use time(t) instead of Current Time Step (ctstep).
And it does work. The flow direction is correct.
Really pretty thanks!!!

April 8, 2015, 03:19	Pulsatile Inlet & Opening Outlet	#1
zxcvbnm2010 New Member Guan Join Date: Jul 2014 Posts: 6 Rep Power: 11	Hi everyone I have a trouble. I run model as a straight tube. When I set the pulsatile inlet and constant pressure outlet, it will be overflow. So, I change the constant pressure outlet to opening outlet. But the results are really strange. The flow is reverse. How could I get the normal flow direction(In→Out) at any timestep? Thanks a lot for your help and time. Best Regards 0.png 1.jpg 2.jpg

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
elbow: boundary conditions for inlet and outlet	cgoe	OpenFOAM Running, Solving & CFD	1	November 8, 2014 13:26
Outlet Backflow problem in simulating pulsatile flow	a.sarami	CFX	0	August 31, 2013 09:41
boundary condition for coupled inlet and outlet	xxxx	OpenFOAM Pre-Processing	2	August 13, 2013 15:51
Unsteady pressure differential between inlet and outlet of the pipe for single phase	joshi20h	FLUENT	0	September 26, 2012 12:41
total pressure boundary problem ==> flow from outlet to inlet!!	mrshb4	OpenFOAM	0	November 20, 2010 12:41

April 8, 2015, 05:52		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	In the post processor draw a contour of the normal component of velocity on the boundary. Then use it to draw a contour of velocity =0. All the flow in one direction will be one colour, all the flow in the opposite direction will be another colour.

April 8, 2015, 17:54		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you mean the backflow is wrong, so how to stop the back flow? Well, the backflow is a result of the conditions you apply. If you are applying a pulsing flow then it sounds like backflow is inevitable. I think you need to go back to basics on this simulation. What are you actually trying to model? What do you know about the flow?

April 9, 2015, 02:01		#6
zxcvbnm2010 New Member Guan Join Date: Jul 2014 Posts: 6 Rep Power: 11	I think I found the problem. Is my expression too complex? Plot it. I really need this wave of inlet velocity. If my expression is incorrect, please help me. Many thanks.

April 9, 2015, 06:08		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can you post your CCL?

April 9, 2015, 08:40		#8
FrankW Member Frank Weise Join Date: Mar 2009 Location: Germany Posts: 55 Rep Power: 17	Why do you use Current Time Step (ctstep) instead of time (t)?

April 9, 2015, 09:31		#9
zxcvbnm2010 New Member Guan Join Date: Jul 2014 Posts: 6 Rep Power: 11	I misunderstand ctstep mean... Thank you all. I use time(t) instead of Current Time Step (ctstep). And it does work. The flow direction is correct. Really pretty thanks!!!