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 hellouch April 1, 2009 08:36

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

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 :confused:)
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.

 emad April 5, 2009 13:49

Quote:
 Originally Posted by hellouch (Post 211591) 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 :confused:) 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

 hellouch April 6, 2009 00:44

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) 493–509
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!

 emad April 21, 2009 03:03

Quote:
 Originally Posted by hellouch (Post 212007) 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) 493–509 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