ABSTRACT
Many properties of fluid flows can be understood based on very general conservation laws. Some of these laws are universal in physics, such as the energy and the momentum conservation laws. Each of them represents a global conservation property, i.e. the total amount of energy and momentum remain unchanged in the system. The other type of conservation laws in fluids are local or Lagrangian: they refer to conservation of a field along fluid trajectories (e.g. the vorticity in 2D) or conservation over a selected set of moving fluid particles (e.g. the velocity circulation over contours made out of moving fluid particles).
