ISA Atmosphere Model
Implement International Standard Atmosphere (ISA)
Libraries:
Aerospace Blockset /
Environment /
Atmosphere
Description
The ISA Atmosphere Model block implements the mathematical representation of the International Standard Atmosphere (ISA) values for ambient temperature, pressure, density, and speed of sound for the input geopotential altitude.
The ISA Atmosphere Model, Extended ISA model, and Lapse Rate Model blocks are identical blocks. The ISA Atmosphere Model block has three implementations:
The default ISA model implements the mathematical representation of the ISA values for ambient temperature, pressure, density, and speed of sound for the input geopotential altitude between sea level (0 m) and tropopause (20000 m).
The extended ISA model implements the mathematical representation of the ISA values for ambient temperature, pressure, density, and speed of sound for the input geopotential altitude between -5000 m and mesopause (84852 m).
The Lapse rate model implements custom lapse rate atmosphere model using the input parameters.
The ISA Atmosphere Model block icon displays the input and output port labels in metric units.
Limitations
In the default model, the block limits the implementation to the geopotential altitude of 0 m (minimum) and 20000 m (maximum). In the extended model, the limits are -5000 meters (minimum) and 84852 meters (maximum). The limits are inclusive.
Density and speed of sound are calculated using a perfect gas relationship.
Ports
Input
Output
Parameters
Algorithms
The dynamic viscosity is computed using [1]:
The kinematic viscosity is computed using [1]:
where:
β — A constant dependent on the reference temperature and dynamic viscosity.
T — Kelvin kinetic temperature.
S — Sutherland constant.
ρ — Mass density of air.
Note
In the Lapse Rate model, the dynamic and kinematic viscosities are computed using the β and S values of air.
References
[1] U.S. Standard Atmosphere., Washington, D.C.: U.S. Government Printing Office, 1976.