The motion of fluids and gases are described with the Navier-Stokes
equation and the equation of
continuity
[11, ]:

These two equations describe the motion of fluids in both two- and
three-dimensional systems.

is the velocity field. denotes the derivative of a
quantity when you follow the flow (as opposed to
) and can be expanded to
. is the density of
the fluid. *p* is the pressure. is the kinematic viscosity and
is the second viscosity. The viscosity of a fluid can under most
circumstances, including the experiments presented in this thesis, be
considered constant. *F* represents external forces such as gravity and the
Coriolis-force.

sparre@cats.nbi.dk