Fluid dynamics is the study of fluid flow. It has two subdisiciplines, aerodynamics and hydrodynamics. Fluid dynamics is used in a wide range of applications. One can calculate the forces on aircrafts, determine flow through pipes or predict weather patterns by using fluid dynamics. Some principles from fluid dynamics are even used in traffic engineering. Fluid dynamics is cross disciplinary and studied in a wide variety of ways.

The foundation of fluid dynamics is the conservation laws. These laws are based off classical mechanics but modified in quantum mechanics and general relativity. From these principles the Reynolds Transport Theorem was created. To model more complex equations of Newtonian fluids, physicists use the Navier-Stokes equations which model the behavior of fluids in a series of differential equations. Computational physics is often used in order to solve these complex problems in which stress and velocity are dependent on linearity.

Definitions

**Compressible Fluid** – The density changes with a change in pressure or temperature.

**Incompressible Fluid** – The density change is negligible with a change in pressure or temperature.

**Viscous Flow** – The fluid friction does not have significant effects on the fluid motion. Viscous flow indicated the Reynolds number is low.

**Inviscid Flow** – The fluid Friction has significant effects on fluid motion. The Reynolds number is high.

**Steady Flow** – The fluid properties throughout the system do not change.

**Unsteady Flow** – The fluid properties change through the system.

**Laminar Flow** – The fluid flow is in parallel layers with no disruptions. The Reynolds number is less than one.

**Turbulent Flow** – There is recirculation and apparent randomness of flow. The Reynolds number is greater than one.

**Newtonian Fluid** – The viscous stresses arise from the flow at every point. These stresses are proportional to the local strain rate over time.

**Non-Newtonian Fluid** – The viscosity of the fluid is dependent on shear rate.