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Non-Newtonian Flow: Power law (2D BFS)

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Old   April 1, 2009, 08:36
Exclamation Non-Newtonian Flow: Power law (2D BFS)
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Harsh Chaudhary
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Hi everyone,
I am a student at IIT Roorkee in India.
I am trying to stimulate 2-Dimensional non-Newtonian flow over a backward facing step. I'm using power law model. But I am not getting the correct results. (Interestingly the values of the recirculation length for a particular Re (say 100) match with the value given for twice the value of Re (Here 200) in my reference paper )
The same mesh is generating very good results for Newtonian flow.

Re: 50 to 400.
n=0.25
Inlet Vel: 2
Inlet Temp: 275k
Density and consistency index are manipulated to give Re the desired value.
Min Viscosity= e(-10)
Max Viscosity= e(+10)
Ref Temp= 0 k (This was 273 earlier , no difference occurred)

Pressure-Velocity coupling: SIMPLE
Discretization>
Pressure: Standard
Momentum: Power Law
Energy: Power Law

Please if anyone can spot any problem in these values do inform me.
Also if you happen to have some study material\Fluent tutorials related to non-Newtonian flow/Backward Facing step/Power Law or Heat transfer for laminar flow in fluent, please do forward it to me.
Any kind of suggestion/guidance will be highly appreciated.

Thanks.
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Old   April 5, 2009, 13:49
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emad khazal
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Quote:
Originally Posted by hellouch View Post
Hi everyone,
I am a student at IIT Roorkee in India.
I am trying to stimulate 2-Dimensional non-Newtonian flow over a backward facing step. I'm using power law model. But I am not getting the correct results. (Interestingly the values of the recirculation length for a particular Re (say 100) match with the value given for twice the value of Re (Here 200) in my reference paper )
The same mesh is generating very good results for Newtonian flow.

Re: 50 to 400.
n=0.25
Inlet Vel: 2
Inlet Temp: 275k
Density and consistency index are manipulated to give Re the desired value.
Min Viscosity= e(-10)
Max Viscosity= e(+10)
Ref Temp= 0 k (This was 273 earlier , no difference occurred)

Pressure-Velocity coupling: SIMPLE
Discretization>
Pressure: Standard
Momentum: Power Law
Energy: Power Law

Please if anyone can spot any problem in these values do inform me.
Also if you happen to have some study material\Fluent tutorials related to non-Newtonian flow/Backward Facing step/Power Law or Heat transfer for laminar flow in fluent, please do forward it to me.
Any kind of suggestion/guidance will be highly appreciated.

Thanks.
Dear Mr. Harsh Chaudhary
I can help you if Please, send me all dimesion of your backward facing step and your reference
AND send me your using Re equation
With best regards
EMAD
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Old   April 6, 2009, 00:44
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Harsh Chaudhary
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The dimensions of the (2D) grid are :
upstream 1hX15h
downstream 2hX30h
here h is the upstream inlet breadth
So the step height is 1h.

Re= (2h)^n (u)^(2-n) ρ / μ
u: inlet velocity (uniform at inlet)
n= 0.25 (for validation with ref)
rest information is given in my prev post.

My reference is a paper by Choi et al. "Numerical study of the impact of non-Newtonian blood behavior on flow over a two-dimensional backward facing step" Biorheology 42 (2005) 493509
They have taken blood as the reference fluid and used the Carreau model for non-Newtonian flow.
I was trying to use power fluid model to regenerate results close to this. I also tried using Carreau model but again the results didn't match.

Some of my results:

Re=100
Choi (Xr/s) : 2.8
Our result (carreau) (Xr/s): 1.938
Our result (Power law)(Xr/s): 4.82
Re=200
Choi (Xr/s) : 4.8
Our result (carreau) (Xr/s) : 3.877
Our result (Power law)(Xr/s): 8.6
Xr : Reattachment length from step

Please do help me out if you find something wrong in this....
Thanks a LOT!
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Old   April 21, 2009, 03:03
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emad khazal
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Quote:
Originally Posted by hellouch View Post
The dimensions of the (2D) grid are :
upstream 1hX15h
downstream 2hX30h
here h is the upstream inlet breadth
So the step height is 1h.

Re= (2h)^n (u)^(2-n) ρ / μ
u: inlet velocity (uniform at inlet)
n= 0.25 (for validation with ref)
rest information is given in my prev post.

My reference is a paper by Choi et al. "Numerical study of the impact of non-Newtonian blood behavior on flow over a two-dimensional backward facing step" Biorheology 42 (2005) 493509
They have taken blood as the reference fluid and used the Carreau model for non-Newtonian flow.
I was trying to use power fluid model to regenerate results close to this. I also tried using Carreau model but again the results didn't match.

Some of my results:

Re=100
Choi (Xr/s) : 2.8
Our result (carreau) (Xr/s): 1.938
Our result (Power law)(Xr/s): 4.82
Re=200
Choi (Xr/s) : 4.8
Our result (carreau) (Xr/s) : 3.877
Our result (Power law)(Xr/s): 8.6
Xr : Reattachment length from step

Please do help me out if you find something wrong in this....
Thanks a LOT!
Dear Mr. Hellouch
Iam very sorry to late for reply quickly, I run your case and i have same your result.

Sorry
Many thanks
emad
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