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Plane poiseuille flow between 2 flat plates

Posted Mar 27, 2017, 6:19 p.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD) Version 5.2a 3 Replies

Anindita Bhattacharya
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Hi everyone,
I am new to COMSOL. I am trying to simulate a plane Poiseuille flow between 2 flat plates with a gap of 0.05 m and a pressure difference of 0.1 Pa over 0.1 m length (giving dP/dx=-1 Pa/m). The fluid is water- dynamic viscosity is 8.9*10^(-4) Pa s.
So, according to ocw.mit.edu/courses/mechanical-engineering/2-25-advanced-fluid-mechanics-fall-2013/equations-of-viscous-flow/MIT2_25F13_Couet_and_Pois.pdf
my maximum velocity should be 0.35 m/s but according to the simulation file I have attached, I am getting
something close to 0.2 m/s.
Could you please tell me what I am doing wrong?

Best Regards
Anindita
3 Replies Last Post Mar 28, 2017, 12:03 a.m. EDT
Mohammad Amin Kazemi
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Posted: 7 years ago Mar 27, 2017, 6:46 p.m. EDT

Hi everyone,
I am new to COMSOL. I am trying to simulate a plane Poiseuille flow between 2 flat plates with a gap of 0.05 m and a pressure difference of 0.1 Pa over 0.1 m length (giving dP/dx=-1 Pa/m). The fluid is water- dynamic viscosity is 8.9*10^(-4) Pa s.
So, according to ocw.mit.edu/courses/mechanical-engineering/2-25-advanced-fluid-mechanics-fall-2013/equations-of-viscous-flow/MIT2_25F13_Couet_and_Pois.pdf
my maximum velocity should be 0.35 m/s but according to the simulation file I have attached, I am getting
something close to 0.2 m/s.
Could you please tell me what I am doing wrong?

Best Regards
Anindita

I think the difference arises from the fact that the formulas in the link you sent are derived for 1D flows. But your model is 3D. Try to increase the aspect ratio and see if the difference vanishes.
I didn't check anything else though.
Also, do not expect to get the same answer as the analytical solution when using numerical methods.
Amin,

[QUOTE] Hi everyone, I am new to COMSOL. I am trying to simulate a plane Poiseuille flow between 2 flat plates with a gap of 0.05 m and a pressure difference of 0.1 Pa over 0.1 m length (giving dP/dx=-1 Pa/m). The fluid is water- dynamic viscosity is 8.9*10^(-4) Pa s. So, according to https://ocw.mit.edu/courses/mechanical-engineering/2-25-advanced-fluid-mechanics-fall-2013/equations-of-viscous-flow/MIT2_25F13_Couet_and_Pois.pdf my maximum velocity should be 0.35 m/s but according to the simulation file I have attached, I am getting something close to 0.2 m/s. Could you please tell me what I am doing wrong? Best Regards Anindita [/QUOTE] I think the difference arises from the fact that the formulas in the link you sent are derived for 1D flows. But your model is 3D. Try to increase the aspect ratio and see if the difference vanishes. I didn't check anything else though. Also, do not expect to get the same answer as the analytical solution when using numerical methods. Amin,
Anindita Bhattacharya
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Posted: 7 years ago Mar 27, 2017, 7:20 p.m. EDT
Hi Amin,
Thank you so much. I get much better results, if I have length and depth=0.1 m and width =0.005m. So I guess aspect ratio was the culprit here. What mesh would you however suggest to get a smoother velocity profile?

Best Regards
Anindita
Hi Amin, Thank you so much. I get much better results, if I have length and depth=0.1 m and width =0.005m. So I guess aspect ratio was the culprit here. What mesh would you however suggest to get a smoother velocity profile? Best Regards Anindita
Mohammad Amin Kazemi
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Posted: 7 years ago Mar 28, 2017, 12:03 a.m. EDT

Hi Amin,
Thank you so much. I get much better results, if I have length and depth=0.1 m and width =0.005m. So I guess aspect ratio was the culprit here. What mesh would you however suggest to get a smoother velocity profile?

Best Regards
Anindita

Of course the finer, the better.
You may also play with shape orders and discretization (P2+P1, P3+P2) and see if it gives what you want.
Amin,
[QUOTE] Hi Amin, Thank you so much. I get much better results, if I have length and depth=0.1 m and width =0.005m. So I guess aspect ratio was the culprit here. What mesh would you however suggest to get a smoother velocity profile? Best Regards Anindita [/QUOTE] Of course the finer, the better. You may also play with shape orders and discretization (P2+P1, P3+P2) and see if it gives what you want. Amin,

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