Standard Atmosphere

Reliable atmospheric data is an important necessity in aerodynamics. Design of aeroplanes, missiles and spacecraft depends on values of atmospheric pressure, density, temperature and other variables. It is impossible to arrive at analytical expressions for these. One has to rely on correlations of experimental data. Scientists have been making extensive measurements of atmospheric data at different location upon the earth and at different times. The result is the database The US Standard Atmosphere, which of course undergoes frequent updating.

The sealevel properties of air according to U.S. Standard Atmosphere are as shown in Table below.

Table 2.1 : Sealevel Properties according to US Standard Atmosphere

 

Property	Value in SI units
Temperature,T	288.15 K
Pressure,p	101.33kPa
Density, $\rho$	1.25 $kg/m^3$
Specific Weight, $\gamma$	12.014 $N/m^3$
Viscosity, $\mu$	$1.789\times 10^{-5}N.s/m^2$

The temperature variation with altitude is also given by the U.S. standard atmosphere and is shown plotted in Fig.2.5. The region of interest for aerodynamic work (up to a height of 20kms above sealevel)divides itself into two parts - Troposphere and Stratosphere. These have been sketched in Fig.2.

 

Figure 2.5 : Atmospheric temperature at different altitudes

Figure 2.6 : Troposphere and Stratosphere

 

Figure 2.5 : Atmospheric temperature at different altitudes

Figure 2.6 : Troposphere and Stratosphere