0
problem in results

Hi all, Greetings for the day I used gnuplot to plot the drag force and i got F(drag)=1.2*10^(-6), for flow past a cylinder with blockage ratio=0.3 and Re=100 and calculated Cd(drag coeff.) using it. I got the Cd value totally wrong. Is the unit of the Force in newtons? I have checked the problem specification again and again but still i can't find the problem. I am using parabolic profile velocity at inlet.I couldn't attach my case file here because i am not getting any options for that. Can anyone tell me where could have i gone wrong. Thanks in advance regards Subhankar


OpenFOAM 21-11-16, 12:40 p.m. SUBHANKAR

Answers:

0

Hi Subhankar,

I was facing the same problem a few days back. I was making a mistake while selecting the units for area. Use the same scale as you used for geometry creation for area. As you know, Drag co-eff= 2D/(rho*A*V^2), check the units for D, rho, A and V and you will solve your problem.
Viraj

21-11-16, 12:55 p.m. virajbelekar

Hi
thanks for the quick reply
I am doing 2-D simulations. So in place of area I am using diameter of the cylinder and i am taking the value of V =maximum velocity at inlet, Since i am using parabolic inlet velocity profile. But for calculating Reynolds number i am using Uavge. Are these steps correct? Also my Value of drag force, D is coming very small.
Subhankar


21-11-16, 2:29 p.m. SUBHANKAR

Also can u please share your email-id so that i can share my files. Otherwise you can ping me at subhankar2020@gmail.com
Thanks and regards
Subhankar


21-11-16, 2:35 p.m. SUBHANKAR

Hi biraj,
If you have problem sharing your email-id, understand completely but I seriously need your help. Please do reply soon.
regards
Subhankar


23-11-16, 2:29 p.m. SUBHANKAR

Hi Subhankar,


Your steps seem to be correct. I would suggest you refer to the below mentioned link for calculating the aerodynamic co-efficients of 2D airfoil: 
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2011/HamidrezaAbedi/report_task_3.pdf

Regards
Viraj


23-11-16, 2:58 p.m. virajbelekar

Login to add comment

0

Hi Viraj, http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2011/HamidrezaAbedi/report_task_3.pdf I was trying to work on this problem. First, for BlockMeshDict File, we need to define Vertices. For that in the PDF, a link is provided, which is not working now. Can you help me with that? it's really tough for me to form the vertices from the given diagram. Thank you very much. Regards, Ankur Garg

17-03-17, 12:58 p.m. ankur_garg

Login to add comment

Log-in to answer to this question.