Glossary - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 338

CFL Courant-Friedrichs-Lewy is a value or condition used to de-

termine the convergence condition for solving hyperbolic
partial differential equations. The CFL number should al-
ways be checked when dealing with transient simulations
(i.e. explicit time marching schemes)

Coanda effect Is the tendency for a stream of fluid to remain attached to a

surface

Compressible flow Fluid flow is considered compressible if there is variation in

its density within the flow domain. This is important when
setting up a CFPD problem so that the density changes are
accounted for

Continuity Is the name given to the mass conservation equation, (e.g.

describes how mass in = mass out)

Convergence When the solution being iterated does not change with each

successive iteration

The mass of fluid per unit volume (kg/m 3 ) Density

Diffussion The process whereby random motion of molecules move

from regions of higher concentration to regions of lower
concentration

Domain The entire region where the mesh encompasses

Drag coefficient An opposing force in the flow direction exerted on an ob-

ject by the fluid flowing around it, normalised by dynamic
pressure and frontal area

Dynamic pressure The pressure relative to a velocity reference

Eddy See vortex

Euler equations Simplified equations of fluid motion which describe the flow

of a compressible inviscid fluid

Eulerian description Describes fluid motion by following an individual fluid par-

ticle as it moves through space and time (compare with
Eulerian description )

Favourable pressure When the static pressure decreases in the direction of the flow

gradient i.e. when the rate of change in pressure is negative (compare

with favourable pressure gradient)

Finite difference A numerical technique to solve differential and integral

(FD) equations (see Sect. 7.21 of topic)

Finite element A numerical technique to solve differential and integral

equations. An alternative to the finite difference and finite
volume

Finite volume (FV) A numerical technique to solve differential and integral

equations (see Sect. 7.22)

Flow separation The fluid boundary layer detaches from a surface when an

adverse pressure gradient dominates the flow

Gauss divergence From vector calculus, which states that the outward flux

theorem through a closed surface (how much fluid flows out of a vol-

ume through its surface) is equal to the volume integral of the
divergence of the vector field inside the volume (total sources