FLAIR is a special-purpose version of PHOENICS, designed to provide an air- and heat-flow simulation facility for the Heating, Ventilating and Air-Conditioning community.

It predicts air-flow patterns and temperature distributions in buildings and other enclosed spaces and so can be used during the design process to detect and avoid uncomfortable air speeds or temperatures.

In addition it can predict effects
of smoke movement, or any other gaseous pollutant, helping to
achieve safe design of buildings, underground systems, aircraft
or train cabins *etc*. It is therefore often used both by regulatory
bodies and by safety consultants.

The data required for the simulation are input to the package
*via* a menu system, in which common terms (such as 'aperture',
'partition', 'heater' and 'fan') are used. Little CFD knowledge
is therefore required to operate FLAIR.

**FLAIR Features:**

**Dimensionality:**
FLAIR allows the simulation of systems which are two- or
three-dimensional in space, and either time-dependent or steady.

**Geometrical features:**
FLAIR can employ three types of coordinate systems:

- Cartesian,
- polar and
- general curvilinear (or body-fitted).

In the case of Cartesian and polar-coordinate systems, the geometry is defined before and independently of the computational grid.

In body-fitted coordinates (BFC's), the geometry is defined with the computational grid, but in such a way as to allow salient features to be identified as separate regions of the grid which are later used for locating boundary conditions.

**Boundary conditions:**
For Cartesian and polar grids, boundary conditions may be linked
to geometrical features; they are then independent of the
computational grid.

For BFC grids, boundary conditions are defined in terms of regions of the grid, but these remain dependent on the rest of the geometry and the computational grid.

**Library of materials:**
Buildings and equipment can be built up from differing materials,
and these can be selected from a built-in library. It is based
on the materials listed in the CIBSE Guide.

**User-defined materials:**
FLAIR allows users to add materials to the existing library if
this does not meet the requirements for a particular simulation.

**Predicted quantities:**
The simulation performed by FLAIR computes values of pressure,
temperature, velocity, turbulent quantities and marker variable
(e.g. smoke concentration), within the domain of interest defined
by the extent of the computational grid (i.e. within and/or
around the enclosure being modelled).

**Gravity:**
FLAIR has a built-in gravity force model; this acts in the
y-direction in 3-dimensional coordinates and in 2-dimensional
x-y or y-z coordinates, or in the z-direction in 2-dimensional
x-z coordinates, depending on the plane in which users choose
to set up their simulation.

**Turbulence modelling:**
FLAIR has a built-in turbulence model, which takes into account
the effect of turbulence on the velocity, temperature and
marker-variable values. The activation and operation of this
turbulence model is automatic, but the user can switch the
turbulence model off, if it is desired, with a press of a button.

Further information on turbulence models is provided, for the benefit of the CFD specialist, in the Encyclopedia.

**Post-processing:**
The post-processor PHOTON allows the results of the calculation
to be viewed graphically, in two or three dimensions, by
displaying contour plots (of temperatures, marker variable or
any other scalar quantity), velocity vectors, streamlines *etc* .

**Units:**
FLAIR works in SI units only (kilograms, seconds, Watts and
degrees Celsius/Kelvin).