Fluid dynamics

The fluid dynamics is a branch of fluid mechanics and deals with moving liquids and gases. It examines, for example, laminar and turbulent flows in open and closed flumes and movements and force ratios in pressure lines.

The basic equation of hydrodynamics is the continuity equation:

With the mass density and the velocity vector

This equation says, among other things, that the mass flow is always the same by a surface. This can be graphically explained as follows: Derive in a tube of water. He does not burst because it accumulates water, the same amount of water needs to come out at the end of the hose, as to flow. If the tube is narrowed at one point, the same amount of water still needs to come out in the end. This means that the water has to flow faster in the narrow piece of tubing as in the wider.

In general, movement of a fluid is described by the Navier-Stokes equations. In the case of low viscosity, the friction effects can be neglected and it is a good approximation, the Euler equation

Which relates the change in velocity of the fluid at a place with the pressure prevailing in the ambient pressure in combination. Thus, it is the equation of motion of the fluid at a high Reynolds number.