Glossary - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 340

Normal stress Also referred to as pressure, it is the component of stress that is

perpendicular or normal to the material (compare with shear
stress )

Potential flow An idealised flow that is irrotational, and inviscid used for

simplifying analysis of fluid flow

Residual The measurement of the difference between the solutions

during CFD—this value should decrease in a convergins
solution

Shear stress The component of stress that occurs in plane with the material

(compare with normal stress )

Skewness A type of descriptor for the quality and shape of a mesh cell

Slip velocity The relative velocity between the particle and the surrounding

fluid

Stability Refers to the numerical stability of the chosen discretisation

scheme whereby with each numerical iteration the solution
converges rather than diverging

Static pressure The pressure based on local atmospheric conditions and is

independent of the flow conditions (compare with dynamic
pressure )

Stokes flow Also called creeping flow, where inertial forces are small com-

pared with viscous forces. Typically the Reynolds number is
less than 1, i.e. Re<<1

Streamline A path in a steady flow field along which a given fluid particle

travels

Surface tension Property of the surface of a liquid that allows it to resist an

external force

Total pressure The combination of static (local atmospheric conditions) and

dynamic (any moving velocity conditions) pressure

Transition regime The region where the flow changes from laminar to turbulent

within the boundary layer

Transport equation A generic equation that represents the various physical pro-

cesses of a flow variable as it moves (i.e. transports) through
a fluid (see Eq. 5.43 in Sect. 5.4)

Turbulent flow Flow where the fluid inertia is dominant and particles move

erratically, mixing greatly throughout the domain

Vapour pressure Pressure at which the vapor of that substance is in equilibrium

with its liquid or solid forms

Viscosity A measure of the resistance of a fluid which is being deformed

by shear stress

Vortex The swirling of a fluid and its reverse current

Vorticity The tendency for elements of the fluid to rotate or spin; defined

as the circulation per unit area at a point in the flow field

Wake The region of recirculating flow immediately behind a moving

solid body, caused by the flow of surrounding fluid around the
body