force coefficient's amplitude

Konstantine · September 22, 2014, 05:59

hi
I am using the icofoam on a Re=100 around a cylinder flow. the frequency of the force coefficients is correct but i am getting wrong amplitude, meaning the oscillation happens around value much higher than it should be according to papers and books
it should be oscillating around 1.44 but it oscillates around 3. any ideas with this happens. I have checked the coefficient formula it is the usual one so no problem there.

pruthvi1991 · March 7, 2015, 15:23

Whats the depth of your domain? I'm referring to the Z-direction. Value of Aref should be chordlength*domaindepth

Konstantine · March 9, 2015, 08:16

thank you for your reply, the truth is that the depth is very small comparing to the diameter of the cylinder like 1/10 of the dimaeter and this possibly could explain the differnece in the forces, Aref should be the actual area against the flow which is the depth times the diameter, probably i have to change the coefficient calculations which i have done but then it was very small. any way good tip but i need to rerun which takes time

pruthvi1991 · March 9, 2015, 12:49

Hello Konstantine,

You do not need to rerun the case. Just use "execFlowFunctionObjects". It is a post processing tool. It will integrate the pressure over the surface. Type "execFlowFunctionObjects" in the directory which has all the time steps.

Konstantine · March 10, 2015, 07:00

i probably need to transform the forces results by dividing with the proper surface rather than Aref=1 which is commonly used. i guess the routine you propose is for the open-foam? i made some tries with the open foam managed to set up something 2d, but the forces were wrong in everything frequency and amplitude. i am running flow around circular cylinder 3d code non commercial or commonly used code. anyway currently i cannot run anything so when i can i will update thread if something did change to the better.

September 22, 2014, 05:59	force coefficient's amplitude	#1
Konstantine New Member Join Date: Sep 2014 Posts: 10 Rep Power: 12	hi I am using the icofoam on a Re=100 around a cylinder flow. the frequency of the force coefficients is correct but i am getting wrong amplitude, meaning the oscillation happens around value much higher than it should be according to papers and books it should be oscillating around 1.44 but it oscillates around 3. any ideas with this happens. I have checked the coefficient formula it is the usual one so no problem there.

March 9, 2015, 12:49	execFlowFunctionObjects	#4
pruthvi1991 Member Pruthvi Join Date: Feb 2014 Posts: 41 Rep Power: 12	Hello Konstantine, You do not need to rerun the case. Just use "execFlowFunctionObjects". It is a post processing tool. It will integrate the pressure over the surface. Type "execFlowFunctionObjects" in the directory which has all the time steps.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
ActuatorDiskExplicitForce in OF2.1. Help	be_inspired	OpenFOAM Programming & Development	10	September 14, 2018 12:12
Sectional force coefficients	tfuwa	OpenFOAM Post-Processing	1	June 27, 2013 07:49
[OpenFOAM] spatial distribution of force coefficients in paraview&openfoam	kkpal	ParaView	1	April 21, 2013 08:15
[General] spatial distribution of force coefficients in paraview&openfoam	kkpal	ParaView	0	April 17, 2013 05:43
Force can not converge	colopolo	CFX	13	October 4, 2011 23:03

March 7, 2015, 15:23		#2
pruthvi1991 Member Pruthvi Join Date: Feb 2014 Posts: 41 Rep Power: 12	Whats the depth of your domain? I'm referring to the Z-direction. Value of Aref should be chordlength*domaindepth

March 9, 2015, 08:16		#3
Konstantine New Member Join Date: Sep 2014 Posts: 10 Rep Power: 12	thank you for your reply, the truth is that the depth is very small comparing to the diameter of the cylinder like 1/10 of the dimaeter and this possibly could explain the differnece in the forces, Aref should be the actual area against the flow which is the depth times the diameter, probably i have to change the coefficient calculations which i have done but then it was very small. any way good tip but i need to rerun which takes time

March 10, 2015, 07:00		#5
Konstantine New Member Join Date: Sep 2014 Posts: 10 Rep Power: 12	i probably need to transform the forces results by dividing with the proper surface rather than Aref=1 which is commonly used. i guess the routine you propose is for the open-foam? i made some tries with the open foam managed to set up something 2d, but the forces were wrong in everything frequency and amplitude. i am running flow around circular cylinder 3d code non commercial or commonly used code. anyway currently i cannot run anything so when i can i will update thread if something did change to the better.