drag coefficient

katiyon · August 7, 2009, 16:36

i have a simple pile in laminar flow in a flat surface , how can i execute drag coefficient?

ghorrocks · August 8, 2009, 07:32

Use CFD-Post to get the forces acting on the body. If you don't already know the area you can use CFD-Post to calculate the area. The velocity and density is usually the freestream values. Then stick it into the drag equation (see http://en.wikipedia.org/wiki/Drag_coefficient).

Be careful about the area you use. Most definitions use frontal area, but aerofoil work uses the wing area so that values are not comparable.

Glenn Horrocks

katiyon · August 8, 2009, 13:43

i can see force distribution on a contour on pipe surface, now how can i use this force distribution to compute drag co.? and then should i use whole area or the area of half-body?

paulo · August 8, 2009, 14:21

Hi,

CFX calculates the forces on every wall boundaries. This happens at the end of the simulation and is written on the OUT file.

Best Regards,

Paulo Rocha

ghorrocks · August 9, 2009, 06:38

Hi,

As Paulo said the total forces are reported in the output file. You can also get them in CFD-Post but using the function calculator. If you do it in CFD-Post you have more things you can do with it, for instance forces on geometric primitives or subsections of the mesh, working out the viscous and form drag components etc etc.

Have a look at the CFD-Post tutorials in the documentation. Pretty much all of them ends with some post-processing, choose one which uses the function calculator.

Glenn Horrocks

gcd2006 · August 11, 2009, 10:33

Quote:

Originally Posted by katiyon

i have a simple pile in laminar flow in a flat surface , how can i execute drag coefficient?

It's very easy,you can search the file which DAT is .out,in the file you can find the force and moment on your wall(which is your model).
Good Luck for you !

sharan · September 29, 2009, 05:56

Hi

I want to know how to calculate drag on a body in rotational flow. I have a rotor rotating with 1500 rpm. CFX is giving the torque (tangential and normal) but how to find out the drag. Do I need to give expressions for that.....
The cross sectional area and the velocity is varying along the span of the rotor. Angular velocity is constant 157.4 rad/s. I also want to plot the Cl and Cd graphs.

I have done the analysis considering two blades (arms) is this better or I should do the analysis for a single one......

Is it possible to export the results of CFX to Fluent ???

can anyone guide me please

thanks

sharantillu@gmail.com

ghorrocks · September 29, 2009, 07:23

Use the force_x/y/z CEL functions to get the forces.

You might be able to export CFX results to Fluent in Workbench V12, not sure I have never tried. If this does not do it then you cannot do it (except meshes, you should be abel to import CFX meshes into Fluent).

cfxmar · September 29, 2009, 08:06

Thank you, Glenn.

The results of force_x()@pile (to get the values of the drag force in the pile) can be exported as a fuction of time

ghorrocks · September 29, 2009, 18:38

I assume that is a question, not a statement - Yes, you can export it. Make a monitor point using the CEL expression. Then you can view the progress of the expression in Solver Manager as the simulation progresses. You can also right click on it and export it.

August 7, 2009, 16:36	drag coefficient	#1
katiyon New Member kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 16	i have a simple pile in laminar flow in a flat surface , how can i execute drag coefficient?

August 8, 2009, 13:43	ansys cfx-post	#3
katiyon New Member kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 16	i can see force distribution on a contour on pipe surface, now how can i use this force distribution to compute drag co.? and then should i use whole area or the area of half-body?

September 29, 2009, 05:56	Drag calculation in rotational flow	#7
sharan New Member sharanappa Join Date: Apr 2009 Location: INDIA (BHARAT) Posts: 8 Rep Power: 17	Hi I want to know how to calculate drag on a body in rotational flow. I have a rotor rotating with 1500 rpm. CFX is giving the torque (tangential and normal) but how to find out the drag. Do I need to give expressions for that..... The cross sectional area and the velocity is varying along the span of the rotor. Angular velocity is constant 157.4 rad/s. I also want to plot the Cl and Cd graphs. I have done the analysis considering two blades (arms) is this better or I should do the analysis for a single one...... Is it possible to export the results of CFX to Fluent ??? can anyone guide me please thanks sharantillu@gmail.com

September 29, 2009, 08:06		#9
cfxmar Member Join Date: Aug 2009 Posts: 42 Rep Power: 16	Thank you, Glenn. The results of force_x()@pile (to get the values of the drag force in the pile) can be exported as a fuction of time Last edited by cfxmar; September 29, 2009 at 08:07. Reason: Correction

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August 8, 2009, 07:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	Use CFD-Post to get the forces acting on the body. If you don't already know the area you can use CFD-Post to calculate the area. The velocity and density is usually the freestream values. Then stick it into the drag equation (see http://en.wikipedia.org/wiki/Drag_coefficient). Be careful about the area you use. Most definitions use frontal area, but aerofoil work uses the wing area so that values are not comparable. Glenn Horrocks

August 8, 2009, 14:21		#4
paulo Member Paulo Alexandre Costa Rocha Join Date: Mar 2009 Posts: 71 Rep Power: 17	Hi, CFX calculates the forces on every wall boundaries. This happens at the end of the simulation and is written on the OUT file. Best Regards, Paulo Rocha

August 9, 2009, 06:38		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	Hi, As Paulo said the total forces are reported in the output file. You can also get them in CFD-Post but using the function calculator. If you do it in CFD-Post you have more things you can do with it, for instance forces on geometric primitives or subsections of the mesh, working out the viscous and form drag components etc etc. Have a look at the CFD-Post tutorials in the documentation. Pretty much all of them ends with some post-processing, choose one which uses the function calculator. Glenn Horrocks

September 29, 2009, 07:23		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	Use the force_x/y/z CEL functions to get the forces. You might be able to export CFX results to Fluent in Workbench V12, not sure I have never tried. If this does not do it then you cannot do it (except meshes, you should be abel to import CFX meshes into Fluent).

September 29, 2009, 18:38		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	I assume that is a question, not a statement - Yes, you can export it. Make a monitor point using the CEL expression. Then you can view the progress of the expression in Solver Manager as the simulation progresses. You can also right click on it and export it.