Supersonic wind tunnel
Encyclopedia
A supersonic wind tunnel is a wind tunnel
that produces supersonic
speeds (1.2<M
<5)
The Mach number and flow are determined by the nozzle
geometry. The Reynolds number is varied changing the density level (pressure in the settling chamber). Therefore a high pressure ratio is required (for a supersonic regime at M=4, this ratio is of the order of 10). Apart from that, condensation or liquefaction can occur. This means that a supersonic wind tunnel needs a drying or a pre-heating facility.
A supersonic wind tunnel has a large power demand leading to only intermittent operation.
Pressure ratio
the total pressure ratio over normal shock at M in test section:
Examples:
with
= 330K: 
= 70K at 
= 4
The velocity range is limited by reservoir temperature
Other problems operating a supersonic wind tunnel include:
Tunnels such as a Ludwieg tube
have short test times (usually less than one second), relatively high Reynolds number, and low power requirements.
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
that produces supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
speeds (1.2<M
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
<5)
The Mach number and flow are determined by the nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
geometry. The Reynolds number is varied changing the density level (pressure in the settling chamber). Therefore a high pressure ratio is required (for a supersonic regime at M=4, this ratio is of the order of 10). Apart from that, condensation or liquefaction can occur. This means that a supersonic wind tunnel needs a drying or a pre-heating facility.
A supersonic wind tunnel has a large power demand leading to only intermittent 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
= 330K: = 70K at = 4The velocity range is limited by reservoir temperature
Power requirements
The power required to run a supersonic windtunnel is enormous, of the order of 50 MW per square meter of test section. For this reason most wind tunnels operate intermittently using energy stored in high-pressure tanks. These windtunnels are also called intermittent supersonic blowdown wind tunnels (of which a schematic preview is given below). 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.Other problems operating a supersonic wind tunnel include:
- adequate supply of dry air
- wall interference effects
- high-quality instruments capable of rapid measurements due to short run times on intermittent tunnels
Tunnels such as a Ludwieg tube
Ludwieg tube
A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached.-Principle:...
have short test times (usually less than one second), relatively high Reynolds number, and low power requirements.
See also
- Wind tunnelWind tunnelA wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
- Low speed wind tunnel
- High speed wind tunnel
- Hypersonic wind tunnelHypersonic wind tunnelA hypersonic wind tunnel is designed to generate a hypersonic flow field in the working section. The speed of these tunnels vary from Mach 5 to 15. As with supersonic wind tunnels, these types of tunnels must run intermittently with very high pressure ratios when initializing.Since the temperature...
- Ludwieg tubeLudwieg tubeA Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached.-Principle:...
- Shock tubeShock tubeFor the pyrotechnic initiator, see Shock tube detonatorThe shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale...