vorticity

Marco

Hello. The definition of vorticity, for curved closed streamlines,according to my understanding, is local spin, local rotation of a fluid parcel on its own axis.

The math definition is twice the angular velocity, but is it the angular velocity of whole fluid around a specified origin or the angular velocity of the fluid element on its own axis?

For example, a planet could orbit another bigger planet in a certain time, but orbit on itself at a much slower or faster speed, completing multiple revolution on itself in justone turn around the bigger planet. So, to me,for vorticity, we are talking about the angular velocity relative to the fluid element axis and not to the fixed origin.

thanks for any clarification.