Question

Which of these is an acceptable tag for Lagrangian parcels?

(a) Parcel’s centre of mass at instantaneous time

(b) Parcel’s centre of pressure at instantaneous time

(c) Parcel’s centre of mass at initial time

(d) Parcel’s centre of pressure at initial time

I have been asked this question in an internship interview.

Enquiry is from Governing Equations topic in portion Governing Equations of Fluid Dynamics of Computational Fluid Dynamics

Answer 1

The correct answer is (c) Parcel’s centre of mass at initial time

To elaborate: Parcel’s centre of pressure is not suitable as it depends not only on position but on many variables too. Instantaneous time continuously varies along with the path. So, it cannot be a tag.