Unit II High Speed Wind TUnnels

High-Speed Wind Tunnels

• High-speed tunnels are those with test-section speed more than 650 kmph. 
• The power to drive a low-speed wind tunnel varies as the cube of the test-section velocity. Although this rule is not valid for the highspeed regime, the implication of rapidly increasing power requirement with increasing test-section speed is true for high-speed tunnels also.
•  Because of the power requirements, high-speed wind tunnels are often of the intermittent type in which energy is stored in the form of pressure or vacuum or both and is allowed to drive the tunnel only a few seconds out of each pumping hour.
• Even though the flow in the Mach number range from 0.5 to 5.0 is usually termed high-speed flow, the tunnels with test–section Mach number less than 0.9 are generally grouped and treated under subsonic wind tunnels. 
• Wind tunnels with Mach numbers from 1.5 to 5.0 are classified as supersonic tunnels 
• And those with Mach number more than 5 are termed hypersonic tunnels. 
• The wind tunnels in the Mach number range from 0.9 to 1.5 are called transonic tunnels.

High-speed tunnels are generally grouped into intermittent and continuous operation tunnels, based on the type of operation. The intermittent tunnels are further divided into blow down tunnels and induction tunnels, based on type of the operational procedure.

The intermittent blowdown and induction tunnels are normally used for Mach numbers from 0.5 to about 5.0, and the intermittent pressure-vacuum tunnels are normally used for higher Mach numbers. The continuous tunnel is used throughout the speed range. Both intermittent and continuous tunnels have their own advantages and disadvantages.