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Atmosphere

The atmosphere module provides standard atmosphere models.

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from flow_state import atmosphere

AtmosphereState

A named tuple returned by atmosphere models:

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from flow_state.atmosphere import AtmosphereState

# Fields
AtmosphereState(
    temperature: float,  # Temperature [K]
    pressure: float,     # Pressure [Pa]
    density: float,      # Density [kg/m^3]
)

USSA76

US Standard Atmosphere 1976. Valid from 0 to 86 km.

Function

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from flow_state import atmosphere

atmosphere.ussa76(altitude: float) -> AtmosphereState

Parameters:

  • altitude: Geometric altitude in meters (0 to 86,000)

Returns: AtmosphereState with temperature, pressure, and density

Example

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from flow_state import atmosphere

# Sea level
sl = atmosphere.ussa76(0)
print(f"Sea level: T={sl.temperature:.1f} K, p={sl.pressure:.0f} Pa")

# 30 km altitude
h30 = atmosphere.ussa76(30_000)
print(f"30 km: T={h30.temperature:.1f} K, p={h30.pressure:.1f} Pa")

CIRA86

COSPAR International Reference Atmosphere 1986. Valid from 0 to 120 km with latitude and seasonal variations.

Class

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from flow_state import atmosphere

cira = atmosphere.CIRA86(latitude: int = 45, month: int = 1)
state = cira(altitude: float) -> AtmosphereState

Parameters:

  • latitude: Latitude in degrees North (0, 10, 20, ..., 80)
  • month: Month (1 = January, ..., 12 = December)

Example

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from flow_state import atmosphere

# Winter polar atmosphere
winter_polar = atmosphere.CIRA86(latitude=70, month=1)

# Summer equatorial atmosphere  
summer_equatorial = atmosphere.CIRA86(latitude=0, month=7)

# Compare at 50 km
h = 50_000
polar = winter_polar(h)
equatorial = summer_equatorial(h)

print(f"Polar (70 deg N, Jan): T={polar.temperature:.1f} K")
print(f"Equatorial (Jul):  T={equatorial.temperature:.1f} K")

Registry

Get atmosphere models by name:

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from flow_state.atmosphere import get_atmosphere_model

get_atmosphere_model(name: str) -> Callable[[float], AtmosphereState]

Parameters:

  • name: Model name ("ussa76" or "cira86")

Returns: Callable that takes altitude and returns AtmosphereState

Available Models

Name Model
"ussa76" US Standard Atmosphere 1976
"cira86" CIRA86 (default: 45 deg N, January)

Custom Atmosphere Models

Any callable with signature (altitude: float) -> AtmosphereState can be used:

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from flow_state import solve
from flow_state.atmosphere import AtmosphereState

def isothermal_atmosphere(altitude: float) -> AtmosphereState:
    """Simple isothermal atmosphere for testing."""
    T = 250.0  # Constant temperature
    p = 101325 * math.exp(-altitude / 7400)  # Scale height 7.4 km
    rho = p / (287.05 * T)
    return AtmosphereState(temperature=T, pressure=p, density=rho)

state = solve(mach=7.0, altitude=30_000, atm=isothermal_atmosphere)