How to create the length of the recirculation zone in post-processing in ansys

Gkchpa · June 23, 2020, 16:49

hello, I would like to Give a length scale of circulation zone for the turbulent flow aster generating Streamlines as shown in the picture.
Do anyone has an idea how to give than in Ansys or do I need to Use any other MS office application

Thank you

flotus1 · June 23, 2020, 19:19

The usual way to determine the reattachment point is through the sign change of wall shear stress.
With the images of streamlines you have here, one could only eyeball an approximate value. Not exactly the most scientific approach.

FMDenaro · June 24, 2020, 03:26

I agree, the point of zero normal derivative of the streamwise component is a correct quantitative measure.

Gkchpa · June 24, 2020, 18:22

Thank you for the reply,

I had plotted skin friction but didn't get any negative values? might be the solution wrong?

FMDenaro · June 24, 2020, 18:26

Quote:

Originally Posted by Gkchpa

Thank you for the reply,

I had plotted skin friction but didn't get any negative values? might be the solution wrong?

You did something wrong in the evaluation

Gkchpa · June 24, 2020, 18:31

surface streamlines ..
Incompressible flow
Inlet velocity 4.5m/s
Atmospheric outlet pressure
K epsilon , wall enhanced

solution converged at around 450 iter

flotus1 · June 25, 2020, 01:37

Almost there. What we need here is the streamwise component of the wall shear stress. Alternatively, the wall-normal derivative of the streamwise velocity will do.
You are plotting skin friction coefficient, which Fluent derives from the magnitude of the wall shear stress vector. Hence why it only has positive values.

Gkchpa · June 25, 2020, 11:29

Thanks for your reply, Can We assume point where Cf is Zero as flow separation point?

flotus1 · June 25, 2020, 12:39

That should also work.

June 23, 2020, 19:19		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	The usual way to determine the reattachment point is through the sign change of wall shear stress. With the images of streamlines you have here, one could only eyeball an approximate value. Not exactly the most scientific approach. FMDenaro and Gkchpa like this.

June 24, 2020, 03:26		#3
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	I agree, the point of zero normal derivative of the streamwise component is a correct quantitative measure. Gkchpa likes this.

June 25, 2020, 01:37		#7
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Almost there. What we need here is the streamwise component of the wall shear stress. Alternatively, the wall-normal derivative of the streamwise velocity will do. You are plotting skin friction coefficient, which Fluent derives from the magnitude of the wall shear stress vector. Hence why it only has positive values. Gkchpa likes this.

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June 25, 2020, 11:29		#8
Gkchpa Member kumar Join Date: Dec 2019 Posts: 33 Rep Power: 6	Thanks for your reply, Can We assume point where Cf is Zero as flow separation point?

June 25, 2020, 12:39		#9
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	That should also work.