Fluid mechanics is the study of the macroscopic physical behaviour of fluids. Fluids are specifically liquids and gases though some other materials and systems can be described in a similar way. The solution of a fluid dynamic problem typically involves calculating for various properties of the fluid, such as velocity, pressure, density, and temperature, as functions of space and time. Fluid mechanics is a subdiscipline of continuum mechanics, as illustrated in the following table:

Fluid mechanics has a wide range of applications. For example, it is used in calculating forces and moments on aircraft, the mass flow of petroleum through pipelines, and in prediction of weather patterns. Fluid mechanics offers a mathematical structure that underlies these practical discipines which often also embrace empirical and semi-empirical laws, derived from flow measurement, to solve practical problems.

Overview of fluid mechanics

Newtonian versus non-Newtonian fluids

Sir Isaac Newton showed how stress and the rate of change of strain are related in a simple way for many familiar fluids, such as water and air. These Newtonian fluids are characterised by a simple viscosity.

However, some other materials, such as milk and blood, and also some plastic solids, have more complicated non-Newtonian stress-strain behaviours. These are studied in the sub-discipline of rheology.

Applications

• Acoustics
• Aerodynamics
• Aeroelasticity
• Aeronautics
• Fluid power
• Hemodynamics
• Hydraulics
• Meteorology
• Oceanography
• Pneumatics

Fluid phenomena

The following observed fluid phenomena can be characterised and explained using fluid mechanics:

• Boundary layer
• Coanda effect
• Convection cell
• Rossby wave
• Shock wave
• Soliton
• Turbulence
• Venturi effect
• Vortex
• Wave drag