Plotting the dragforce vs the distance

lbergmann · July 31, 2015, 06:14

I have made a "drawing" of the plot that I was hoping to get. I am not completely convinced that it is possible to do. But if anyone knew it might be in here.
http://imgur.com/yMbtGki

I calculate the dragforce by integrating the pressure in the direction that I am interested in on the surface. Bur this only gives me the total drag force and as seen in the plot we are interested in showing in a 2d plot where this is on the body.

ghorrocks · July 31, 2015, 06:46

I do not understand what you are saying.

CFD usually returns pressure and shear force over surfaces. You then do area integrals to get the total force on the surface. You appear to show a simple integral (a line integral?) of force, where force exists at points. This does not make sense - or please explain further if I have missed something.

lbergmann · July 31, 2015, 06:49

If we imagine I cut the body I have into thin slices. I then want to plot the posistion of the slice along the x-axis and the drag on this particular slice on the y-axis. The integral (or sum) of the drag on all slices should then be the total drag on the body.

ghorrocks · July 31, 2015, 07:07

This can be done in CFD-Post.

I would do this by cutting the thin strip out of your body and calculating the drag force on it. Then export the data. Then advance the strip to the next location and repeat. You can automate this process using a session file.

The load the exported data in a maths package like matlab/python/excel whatever and draw your plot of drag versus X position.

July 31, 2015, 06:14	Plotting the dragforce vs the distance	#1
lbergmann New Member Line Bergmann Join Date: Sep 2013 Posts: 20 Rep Power: 13	I have made a "drawing" of the plot that I was hoping to get. I am not completely convinced that it is possible to do. But if anyone knew it might be in here. http://imgur.com/yMbtGki I calculate the dragforce by integrating the pressure in the direction that I am interested in on the surface. Bur this only gives me the total drag force and as seen in the plot we are interested in showing in a 2d plot where this is on the body.

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July 31, 2015, 06:46		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I do not understand what you are saying. CFD usually returns pressure and shear force over surfaces. You then do area integrals to get the total force on the surface. You appear to show a simple integral (a line integral?) of force, where force exists at points. This does not make sense - or please explain further if I have missed something.

July 31, 2015, 06:49		#3
lbergmann New Member Line Bergmann Join Date: Sep 2013 Posts: 20 Rep Power: 13	If we imagine I cut the body I have into thin slices. I then want to plot the posistion of the slice along the x-axis and the drag on this particular slice on the y-axis. The integral (or sum) of the drag on all slices should then be the total drag on the body.

July 31, 2015, 07:07		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	This can be done in CFD-Post. I would do this by cutting the thin strip out of your body and calculating the drag force on it. Then export the data. Then advance the strip to the next location and repeat. You can automate this process using a session file. The load the exported data in a maths package like matlab/python/excel whatever and draw your plot of drag versus X position.