Forcecoeffs Cd = Total or skin

kaaja · April 16, 2018, 05:42

H
The Cd that is produced by "forceCoeffs", is the coefficient for total drag (both skin and pressure) or only skin-friction?

tomf · April 17, 2018, 09:19

In principle total, but the description on openfoam.com would indicate that the viscous, pressure and porous parts can be obtained separately as well.

This is not found in the openfoam.org description. So it depends on what version you are using.

Regards,
Tom

kaaja · April 17, 2018, 10:41

Thanks for replying!
I use openFoam 5.0.
The variable name I get out is Cd, which I guess indicates that it is total, but I am not sure.
edit: I am using openfoam.org's version, so I guess it is total then?

tomf · April 17, 2018, 12:26

Hi,

Yes it is.

Regards,
Tom

kaaja · April 17, 2018, 14:51

Ok.
Thank you very much for helping!

Another question.
Do you know if there is some way to obtain the viscous, pressure and porous parts separately in the openfoam.org version?

tomf · April 18, 2018, 04:51

Yes, if you use the forces functionObject. That will split it directly in several force and moment vectors in Cartesian coordinates. You would have to get the coefficients yourself based on the correct direction, surface area and velocity reference.

Regards,
Tom

kaaja · April 18, 2018, 05:25

Ok. Thanks again!

April 16, 2018, 05:42	Forcecoeffs Cd = Total or skin	#1
kaaja Member Join Date: Apr 2017 Posts: 68 Rep Power: 9	H The Cd that is produced by "forceCoeffs", is the coefficient for total drag (both skin and pressure) or only skin-friction?

April 17, 2018, 09:19		#2
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 647 Rep Power: 32	In principle total, but the description on openfoam.com would indicate that the viscous, pressure and porous parts can be obtained separately as well. This is not found in the openfoam.org description. So it depends on what version you are using. Regards, Tom kaaja likes this.

April 17, 2018, 12:26		#4
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 647 Rep Power: 32	Hi, Yes it is. Regards, Tom kaaja likes this.

April 18, 2018, 04:51		#6
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 647 Rep Power: 32	Yes, if you use the forces functionObject. That will split it directly in several force and moment vectors in Cartesian coordinates. You would have to get the coefficients yourself based on the correct direction, surface area and velocity reference. Regards, Tom kaaja likes this.

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April 17, 2018, 10:41		#3
kaaja Member Join Date: Apr 2017 Posts: 68 Rep Power: 9	Thanks for replying! I use openFoam 5.0. The variable name I get out is Cd, which I guess indicates that it is total, but I am not sure. edit: I am using openfoam.org's version, so I guess it is total then?

April 17, 2018, 14:51		#5
kaaja Member Join Date: Apr 2017 Posts: 68 Rep Power: 9	Ok. Thank you very much for helping! Another question. Do you know if there is some way to obtain the viscous, pressure and porous parts separately in the openfoam.org version?

April 18, 2018, 05:25		#7
kaaja Member Join Date: Apr 2017 Posts: 68 Rep Power: 9	Ok. Thanks again!