Glossary

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Glossary of Terms for Fluid Dynamics

Add as you feel necessary. When needed, provide a link to a reference page or other terms.

Purpose: Many of the terms on this list have multiple definitions depending on context. The context for these definitions is geophysical and environmental fluid dynamics.

Disclaimer: this list is mostly the result of googling, and as such should not be referenced directly.

Note: The AMS Glossary is a good source for definitions, should the definition that you seek not be available below.


A-D

Barotropic fluid
A fluid in which density is only a function of pressure. Fluids with constant density are necessarily barotropic.
Baroclinic motion
Motion caused by the misallignment of the surfaces of constant pressure and constant density.
Boundary Layer
Region near a surface in which friction becomes important.
- plane
The - plane approximation assumes that the Coriolis frequency varies linearly with latitude i.e. . and where is the period of Earth's rotation, is the reference latitude, and is the mean radius of the Earth. Wikipedia's entry on this is a good one. cf. -plane
Capillary Wave
Waves in which the dominant restoring force is due to surface tension. Typical length scales are under 7cm.
Chaotic Advection
The advection of particles under a chaotic flow map or dynamical system.
Characteristic Scale
This scale is context dependent. In an engineering situation like a jet out of a small hole one scale is given by the size of the hole, and another, less easily quantifiable scale will be the length over which the jet mixes with the ambient fluid.
Correlation Time
The time it takes for the auto correlation function of a process to decrease by a given amount.
Direct Numerical Simulation (DNS)
Simulation in which you make no assumption on turbulence, and typically attempt to resolve as much as possible. cf. LES

E-J

Energy Cascade
When the coherent structures of the continuum move to smaller and smaller scales until viscosity causes dissipation.
Enstrophy
, the norm squared of the vorticity over a given domain.
- plane
The - plane approximation assumes that the Coriolis frequency is constant in latitude i.e. . Where , is the period of Earth's rotation, and is the reference latitude. cf. -plane
Isentropic Surface
A surface of constant entropy.
Gravity Wave
A wave in which the dominant restoring force is due to gravity acting to restore displaced mass.
Gyre
A vortex, a region dominated by a coherent rotating structure.
Halocline
Region with a high gradient in salinity. See also pycnocline and thermocline
Internal Wave
Waves in which the displaced quantity is an isopycnal. These can include gravity waves and Rossby waves.

K-Q

Large Scale Flow
In geophysical fluid dynamics this refers to the flow dominated by the Earth's rotation, so almost geostrophic flow.
Large Eddy Simulation
A simulation in which a turbulence model has been included to approximate small scale motion and thus reduce the complexity of the problem.
Normal Mode
For a linear PDE, the normal modes are the functions which describe the spatial structure of the standing waves that solve that PDE. We can then approximate any wave that solves the PDE, including non-standing waves, by using the normal modes as a basis
Pycnocline
Region with a high gradient in density. See also halocline and thermocline

R-Z

Rossby Wave
Waves in which the dominant restoring force is to due the conservation of potential vorticity.
Surface Wave
Waves in which the displaced quantity is a water-air interface. These can include gravity waves, Rossby waves, and capillary waves.
Thermocline
Region with a high gradient in temperature. See also halocline and pycnocline