Talk:Vorticity

Edit wars and others

(William M. Connolley 19:16, 25 Jun 2004 (UTC)) I've made some minor changes, and also removed the ref (and hence its section). This needs justifiying. The justification is twofold: firstly the ref'd defn isn't very good. But more importantly, the ref def doesn't include anything that isn't in the wiki article. So there is no point in referring people to it: they will learn nothing new. If its there to bolster claims in the edit war, it belongs here on the talk page and we'll discuss it: but still not on the article page.

As to the edit war: vorticity *is* its definition. Its not a natural-language word. If the definition is difficult or confusing then some text trying to explain it may help. But in that case you have to be very careful that the explanatory text is accurate.

Pmurray bigpond.com 23:20, 22 February 2006 (UTC)

The article mentions "vorticity" moving from place to place. Is this related to the conservation of angular momentum? It might be worthwhile mentioning it if so. I suppose that angular momentum density would be equal to the vorticity times the density of the fluid or something.

There is indeed a close relation between the two ideas, because ω is twice the local angular rotation rate. So the angular momentum of a small spherical blob in the fluid, of moment of inertia I, is (0.5 I ω) (see Batchelor eqn 2.3.12 & 5.2.2). But you'ld need to keep tabs on I, as the fluid distorts, as well as ω. The constancy of the strength of a (small circular) vortex-tube in inviscid flow is essentially a statement of the conservation of the angular momentum within it (see Batchelor, eq 5.3.4). Linuxlad 09:55, 23 February 2006 (UTC)

Misprint or my bug?

Somewhat counter-intuitively, an irrotational fluid can have a non-zero angular velocity (e.g. a fluid rotating around an axis with its angular velocity inversely proportional to the distance to the axis has a zero vorticity)

It should probably be azimuthal velocity. For a simple cylindrical rotating case rot V = 1/r*(d(r V_phi)/dr ). When V_phi=1/r then rot V = 0.

I'm not changing the page because I may be wrong but still check this out, pls.

Best regards, Step.

Yes it's rv=constant in a 'free vortex'. The description of forced and free vortices in vortex uses the term 'tangential velocity' which may be preferable to 'azimuthal' (which suggests angular rather than linear measure). Linuxlad 12:57, 9 March 2006 (UTC)

Yep, I agree. 'Tangential' seems to be the correct word there... Although not to introduce linear velocity at all it may be better just to change

(e.g. a fluid rotating around an axis with its angular velocity inversely proportional to the distance to the axis has a zero vorticity)

to

(e.g. a fluid rotating around an axis with its angular velocity inversely proportional to the square of the distance to the axis has a zero vorticity)

or something like that.

--194.85.80.92 18:54, 9 March 2006 (UTC)