Supersonic wind tunnel


A supersonic wind tunnel is a wind tunnel that produces supersonic speeds
The Mach number and flow are determined by the nozzle geometry. The Reynolds number is varied by changing the density level. Therefore, a high pressure ratio is required. Apart from that, condensation of moisture or even gas liquefaction can occur if the static temperature becomes cold enough. This means that a supersonic wind tunnel usually needs a drying or a pre-heating facility.
A supersonic wind tunnel has a large power demand, so most are designed for intermittent instead of continuous operation.

Restrictions for supersonic tunnel operation

Minimum required pressure ratio

Optimistic estimate:
Pressure ratio the total pressure ratio over normal shock at M in test section:
Examples:

Temperature effects: condensation

Temperature in the test section:
with = 330 K: = 70 K at = 4
The velocity range is limited by reservoir temperature

Power requirements

The power required to run a supersonic wind tunnel is enormous, of the order of 50 MW per square meter of test section cross-sectional area. For this reason most wind tunnels operate intermittently using energy stored in high-pressure tanks. These wind tunnels are also called intermittent supersonic blowdown wind tunnels. Another way of achieving the huge power output is with the use of a vacuum storage tank. These tunnels are called indraft supersonic wind tunnels, and are seldom used because they are restricted to low Reynolds numbers. Some large countries have built major supersonic tunnels that run continuously; one is shown in the photo.
Other problems operating a supersonic wind tunnel include:
Tunnels such as a Ludwieg tube have short test times, relatively high Reynolds number, and low power requirements.