
[Sponsors] 
November 20, 2017, 07:24 
drag coeff.

#1 
Senior Member
A. Min
Join Date: Mar 2015
Posts: 291
Rep Power: 9 
Hi foamers
I want to simulate flow around cylinder and calculate drag coeff. with openFoam. In papers calculated Cd is 1.9 but when I compute it with openfoam that is earned 4.3!! Re = 25 (U=1 , rho = 1 , D=1 , nu = 0.04) simpleFoam  my mesh is OK (I think!) Do you know why?! Thanks 

November 20, 2017, 07:36 

#2 
Senior Member
Oskar
Join Date: Nov 2015
Location: Poland
Posts: 185
Rep Power: 7 
It is probably because Your turbulence model assume there is fully turbulent flow in entire domain while in fact there is laminar flow in viscous sublayer. Turbulent viscous is higher than laminar viscous so drag coefficient is too high.
To prevent this You could try to use following transient turbulence model: LangtryMenter komega Shear Stress Transport (SST) If You succeed with Your simulation could You possibly share Your case? Have a nice day. Sheaker 

November 20, 2017, 07:39 

#3  
Senior Member
A. Min
Join Date: Mar 2015
Posts: 291
Rep Power: 9 
Quote:
Dear Oskar Thank you for your answer. as you know my Re number is 25 and in this Re flow regime is laminar. Also I should tell you that I did my simulation similar to : http://nbviewer.jupyter.org/github/s...m/README.ipynb thanks 

November 20, 2017, 08:38 

#4 
Senior Member
Oskar
Join Date: Nov 2015
Location: Poland
Posts: 185
Rep Power: 7 
I'm so sorry. I missed Your Re is 25!(I have just woke up...) I was trying to match drag coef of an airfoil that's why I assume Your case is similar.
Now when I think for a while there are some things You should ask Yourself:  Your coefficients depends on depth of Your mesh. Is Your mesh 1meter depth?  I'm not sure about Your nu value. You are sure?  Your case is incompressible and Your density is set to 1  this is right but as I remember calculation of coefficient is not the same way as in compressible case. You are sure You calculate it in right way? I'm sorry but I can't help better. Have a nice day. Sheaker 

November 20, 2017, 08:45 

#5  
Senior Member
A. Min
Join Date: Mar 2015
Posts: 291
Rep Power: 9 
Quote:
1 yes, my mesh 1meter depth 2 nu is calculated using Re. Re= 25 and other parameter is 1. so n=0.04 3 I'm not sure about this! I'm using the forces code of openFoam. however, thank you 

Tags 
drag, simplefoam 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Difficulty in understanding Coeff. of Drag of Airfoil  Mhrc  Main CFD Forum  0  April 9, 2017 01:38 
How to visualize lift and drag coeff  frossi  CFX  3  February 5, 2017 18:29 
Induced drag, pressure drag, viscous drag.  aleix.de.toro  FLUENT  2  August 24, 2015 18:00 
drag coeff to high  kOmegaSST turbulence model  RugbyGandalf  OpenFOAM  5  February 22, 2011 02:35 
High drag coeff. estimated by Gambit+fluent  M. suuri  FLUENT  6  November 6, 2006 08:02 