Standard Atmosphere Freestream

Set freestream temperature, pressure, density, sound speed, Mach, and Reynolds number from altitude and speed.

visual calculatorCompressible Flow

Read the flow shape before trusting the number.

This page turns a CFD setup into regime, scale, and dominant-effect cues. Adjust the calculator below and compare the moving graphic with the computed result.

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standard atmospherefreestreamMachReynolds

formula

KaTeX rendered

\begin{aligned}\text{rho = p/(R T)}\\[0.35em]\text{a = sqrt(gamma R T)}\\[0.35em]\text{Re = rho U L / mu}\end{aligned}

ASCII source

rho = p/(R T), a = sqrt(gamma R T), Re = rho U L / mu

altitude (km)U (m/s)reference length (m)

T (K)

268.6500

p (Pa)

7.011e+4

rho (kg/m^3)

0.9091

speed of sound (m/s)

328.5779

Mach

0.2435

Re_L

4.294e+6

q (Pa)

2909.1900

nu (m^2/s)

1.863e-5

This simplified ISA model covers the troposphere and lower stratosphere up to 32 km. Use site weather data for final validation cases.

standard atmosphere freestream Mach Reynolds