golfball drag coefficient

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thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

golfball drag coefficient

Postby thschrader » Sun Nov 18, 2018 3:50 pm

Motivation:
https://forum.freecadweb.org/viewtopic.php?f=8&t=32285

Golfball: diameter 45 mm, weight 40 gramms, gives a free-fall speed of 130 km/h (at cf=0,3).
At 130 km/h I get a force of 0,6 N, wich gives a drag-coefficient of 0,49.
Seems a little bit to high. Maybe the dimples are to rough. Or the mesh. Or both.

I ran a laminar steady-state simulation (Re=105000), because cfmesh puts the boundary-elements on a wrong face.
The elements are put at one side of the cube, not at the golfball. Cant figure out why.
Thats the real stuff for a rainy sunday...
model.JPG
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velocity.JPG
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chrisb
Posts: 15808
Joined: Tue Mar 17, 2015 9:14 am

Re: golfball drag coefficient

Postby chrisb » Sun Nov 18, 2018 6:10 pm

Thanks for sharing this. It would be great if you can provide the same for pure sphere of the same diameter.
thschrader
Posts: 1394
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: golfball drag coefficient

Postby thschrader » Sun Nov 18, 2018 9:11 pm

The golfball travels at speeds between 250 (start) and 100 kmh (free-fall),
For a 45 mm ball the Re-numbers are between 100000-200000.
At Re=100000 a smooth sphere has a drag-coefficient of 0,5.
At Re=200000 the drag-coefficient begins to drop down due to flow change from laminar to turbulent.
For rough balls, the flow change happens at much lower Re-numbers (=speed).
https://www.grc.nasa.gov/www/k-12/airpl ... phere.html
https://www.mne.psu.edu/cimbala/me325we ... /intro.pdf

@chris:
I ran a simulation for a smooth sphere (laminar flow, drag-coeffient should be around 0,5 at
Re=100000), but I got a drag of only 0,04, which is obviously wrong.
Here is a nice tutorial, I will try to do that with FC first.
https://mycourses.aalto.fi/pluginfile.p ... enfoam.pdf
sphere_drag.JPG
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UR_
Posts: 844
Joined: Tue Jan 03, 2017 8:42 pm

Re: golfball drag coefficient

Postby UR_ » Sun Nov 18, 2018 9:33 pm

A comparative study of golf ball aerodynamics.png
A comparative study of golf ball aerodynamics.png (45.09 KiB) Viewed 578 times

That's from here: https://people.eng.unimelb.edu.au/imaru ... _Paper.pdf :roll: