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-   -   Fluent no longer know their Drag vs. Re curves ? (http://www.cfd-online.com/Forums/fluent/41267-fluent-no-longer-know-their-drag-vs-re-curves.html)

 R. Koeman June 5, 2006 16:32

Fluent no longer know their Drag vs. Re curves ?

What a stupid article on fluent.com main page:

http://www.fluent.com/news/pr/pr132.htm

They compare:

Evolution of soccer ball drag at high speeds for different ball designs - 1960's to the present day â€" zero degrees orientation to oncoming flow.

At what speed? is it the same Reynold number?

This is not how you would represent drag curve for a spherical object moving in the air: it depends on the Reynold number. They showed last time that Drag can change a lot with a small change in Reynolds number:

http://www.fluent.com/news/pr/img/pr43i3_lg.gif

They should plot the Drag vs Reynold number for the four balls as above, other wise it does not mean anything.

I can bet you they have all about the same curve Drag vs. Re.

The kicker just need more force for the old ball because it is heavier. The heavier ball will also keep a higher speed longer as it will be more difficult for the air to stop it once in flight.

Also I'd rather belive the streamline there: http://www.fluent.com/news/pr/pr43.htm than there: http://www.fluent.com/news/pr/pr132.htm

What do you think?

R.K.

 RiKR0K May 3, 2010 12:43

The links don't work

Quote:
 Originally Posted by R. Koeman ;132961 What a stupid article on fluent.com main page: http://www.fluent.com/news/pr/pr132.htm They compare: Evolution of soccer ball drag at high speeds for different ball designs - 1960's to the present day â€" zero degrees orientation to oncoming flow. At what speed? is it the same Reynold number? This is not how you would represent drag curve for a spherical object moving in the air: it depends on the Reynold number. They showed last time that Drag can change a lot with a small change in Reynolds number: http://www.fluent.com/news/pr/img/pr43i3_lg.gif They should plot the Drag vs Reynold number for the four balls as above, other wise it does not mean anything. I can bet you they have all about the same curve Drag vs. Re. The kicker just need more force for the old ball because it is heavier. The heavier ball will also keep a higher speed longer as it will be more difficult for the air to stop it once in flight. Also I'd rather belive the streamline there: http://www.fluent.com/news/pr/pr43.htm than there: http://www.fluent.com/news/pr/pr132.htm What do you think? R.K.

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