ISA Atmosphere Model

Implement International Standard Atmosphere (ISA)

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Libraries:
Aerospace Blockset / Environment / Atmosphere

Description

The ISA Atmosphere Model block implements the mathematical representation of the international standard atmosphere values for ambient temperature, pressure, density, and speed of sound for the input geopotential altitude.

The ISA Atmosphere Model and Lapse Rate Model blocks are identical blocks. When configured for ISA Atmosphere Model, the block implements ISA values. When configured for Lapse Rate Model, the block implements lapse rate values.

The ISA Atmosphere Model block icon displays the input and output port labels in metric units.

Limitations

• Below the geopotential altitude of 0 km and above the geopotential altitude of the tropopause, temperature and pressure values are held.

• Density and speed of sound are calculated using a perfect gas relationship.

Ports

Input

h (m) — Geopotential height

scalar | array

Geopotential height, specified as a scalar or array.

Data Types: double

Output

T (K) — Temperature

scalar | array

Temperature, returned as a scalar or array, in K.

Data Types: double

a (m/s) — Speed of sound

scalar | array

Speed of sound, returned as a scalar or array, in m/s.

Data Types: double

P (Pa) — Air pressure

scalar | array

Air pressure, returned as a scalar or array, in Pa.

Data Types: double

ρ (kg/m³) — Air density

scalar | array

Air density, returned as scalar or array, in kg/m³.

Data Types: double

Parameters

Change atmospheric parameters — Customize parameters

off (default) | on

Customize various atmospheric parameters to be different from the ISA values. Selecting this check box converts the block from ISA Atmosphere Model to Lapse Rate Model.

Dependencies

Selecting this check box enables the parameters:

• Acceleration due to gravity (m/s^2)

• Ratio of specific heats

• Characteristic gas constant (J/Kg/K)

• Lapse rate (K/m)

• Height of troposphere (m)

• Height of tropopause (m)

• Air density at mean sea level (Kg/m^3)

• Ambient pressure at mean sea level (N/m^2)

• Lowest altitude (m)

Programmatic Use

Block Parameter: custom

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Acceleration due to gravity (m/s^2) — Acceleration

9.80665 (default) | scalar

Acceleration from gravity (g). in m/s², specified as double scalar.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: g

Type: character vector

Values: double scalar

Default: 9.80665

Ratio of specific heats — Ratio of heats

1.4 (default) | scalar

Ratio of specific heats γ, specified as a double value.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: gamma

Type: character vector

Values: double scalar

Default: 1.4

Characteristic gas constant (J/Kg/K) — Gas constant

287.0531 (default) | scalar

Characteristic gas constant (R), specified as double scalar, in J/Kg/K.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: R

Type: character vector

Values: double scalar

Default: 287.0531

Lapse rate (K/m) — Lapse rate

0.0065 (default) | scalar

Lapse rate of the troposphere, specified as double scalar, in K/m.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: L

Type: character vector

Values: double scalar

Default: 0.0065

Height of troposphere (m) — Troposphere height

11000 (default) | scalar

Height of the troposphere (range of decreasing temperatures), specified as double scalar, in m.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: h_trop

Type: character vector

Values: double scalar

Default: 11000

Height of tropopause (m) — Tropopause height

20000 (default) | scalar

Height of the tropopause (range of constant temperature), specified as double scalar, in m.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: h_strat

Type: character vector

Values: double scalar

Default: 20000

Air density at mean sea level (Kg/m^3) — Air density

1.225 (default) | scalar

Air density at mean sea level, specified as double scalar, in Kg/m³.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: rho0

Type: character vector

Values: double scalar

Default: 1.225

Ambient pressure at mean sea level (N/m^2) — Ambient pressure

101325 (default) | scalar

Ambient pressure at mean sea level, specified as double scalar, in N/m².

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: P0

Type: character vector

Values: double scalar

Default: 101325

Ambient temperature at mean sea level (K) — Ambient temperature

288.15 (default) | scalar

Ambient temperature at mean sea level (T₀), specified as double scalar, in K.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: K

Type: character vector

Values: double scalar

Default: 101325

Lowest altitude (m) — Lowest altitude

0 (default) | scalar

Lowest altitude above which temperature and pressure lapse, specified as double scalar, in m. Lowest altitude (m) must be below Height of tropopause.

Dependencies

This parameter is enabled when the Change atmospheric parameters check box is selected.

Programmatic Use

Block Parameter: h0

Type: character vector

Values: double scalar

Default: 0

References

[1] U.S. Standard Atmosphere., Washington, D.C.: U.S. Government Printing Office, 1976.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a