Quick math Q!

[Otispunkmeyer]

What value, in general/typically would you class as being much less than one?

I am just working some things out with creeping flow, but I just need to see what velocities for my particles give Reynolds number of much less than one. Re << 1 For stokes flow and therefore stokes drag (6*pi*mu*R*v). But what do you actually class as being much less than 1? is 0.01 much less than 1?

basically determining when I need to use the usual drag equation (+skin friction) and when to use stokes.

[Simpo Two]

I'd say that anything under a half is much less than one. But then the only thing I know about Reynolds numbers is Parsley sauce

[GadgeS3C]

Not sure if it applies to your situation but my copy of Fluid Mechanics (White) suggests creeping flow below Re <=1.

[Otispunkmeyer]

Going by a graph for the Cd of a sphere (for use in the normal drag equation) they go down to Re of 0.1. So I am going to assume Re << 1 is less than that even. My supervisor agrees, but I guess I should go knock on the door of the guy who teaches this stuff here. He should know!

[Devil2575]

Otispunkmeyer said:

Going by a graph for the Cd of a sphere (for use in the normal drag equation) they go down to Re of 0.1. So I am going to assume Re << 1 is less than that even.

Indeed, my interpretation of 'much less than' would be an order or magnitude less. However I suspect the use of the phrase 'much less than' is due to it not being an exact science and there being something of a fuzzy boundary.

Let us know what you decide to use and how you get on.

I've never played with Reynolds numbers that low, everything I do is in the turbulent region.