The perfomance characteristics are specified by two
characteristic equations: the first relates the flow number
`phic`, the pressure ratio `PR` and the referred
speed `N_T`; the second relates the efficiency `eta`,
the flow number `phic`, and the referred speed `N_T`
[1]. To avoid singularities, the two characteristic equations are
expressed in parametric form by adding a further variable
`beta` (method of beta lines [2]).

The performance maps are thus tabulated into three differents
tables, `tablePhic`, `tablePR` and `tableEta`,
which express `phic`, `PR` and `eta` as a
function of `N_T` and `beta`, respectively, where
`N_T` is the first row while `beta` is the first
column. The referred speed `N_T` is defined as a percentage
of the design referred speed and `beta` are arbitrary lines,
usually drawn parallel to the surge-line on the performance
maps.

`Modelica.Blocks.Tables.CombiTable2D` interpolates the
tables to obtain values of referred flow, pressure ratio and
efficiency at given levels of referred speed and beta.

**Modelling options**

The following options are available to determine how the table is defined:

`Table = 0`: the table is explicitly supplied as matrix parameter.`Table = 1`: the table is read from a file; the string`fileName`contains the path to the files where the tables are stored, either in ASCII or Matlab binary format.

**References:**

- S. L. Dixon:
*Fluid mechanics, thermodynamics of turbomachinery*, Oxford, Pergamon press, 1966, pp. 213. - P. P. Walsh, P. Fletcher:
*Gas Turbine Performance*, 2nd ed., Oxford, Blackwell, 2004, pp. 646.

*13 Apr 2005*by Francesco Casella:

New method for calculating performance parameters using tables.*14 Jan 2005*by Francesco Casella:

Adapted to Modelica.Media.

Compressor model restructured using inheritance.*5 Mar 2004*by Francesco Casella:

First release.

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