Fluid dynamics is the branch of Fluid mechanics that describes the causes of motion, i.e. the forces and torques that can affect fluids, and how these affect their motion.
The equations of fluid dynamics can be derived from the principles of Mechanics (in particular continuum mechanics). More recently they have also been derived from the microscopic statistical picture of moving and interacting particles thanks to the development of Kinetic theory.
Navier-Stokes equation
https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations
Oxford course. Bachelor's book, etc.
https://www.youtube.com/watch?v=pqWwHxn6LNo&list=PL0EC6527BE871ABA3&index=2
https://en.wikipedia.org/wiki/Strain_rate_tensor
See table I made for 3rd year revision
of heat, particles, etc.
https://en.wikipedia.org/wiki/Convection%E2%80%93diffusion_equation
http://www.cfm.brown.edu/people/gk/chap9/node1.html
https://twitter.com/BeamManP/status/1064533238218014726