A Wind Tunnel is tool used in Aerodynamics research to study the effect of air moving past solid objects. A wind tunnel consists of a tubular passage with the object under test mounted in the middle. Air is made to move past the objects by a powerful fan system or other means. The test object, often called a wind tunnel model is instrumented with suitable sensors to measure aerodynamic forces, pressure distribution, or other aerodynamic related characteristics.
1.2 History:- The earliest wind tunnels were invented towards the end of the 19th century, in the early days of aeronautic research, when many attempted to develop successful heavier than air flying machines. The wind tunnel was envisioned …show more content…
Sir George Cayley (1773-1857) also used a whirling arm to measure the drag and lift of various airfoils. His whirling arm was 5 feet long and attained top speed between 10 to 20 feet per second. Francis Herbert Wenham (1824-1908), a council member of Aeronautical Society of Great Britain, addressed issues of wind tunnel by inventing, designing and operating the first enclosed wind tunnel in 1871. Wenham and his colleague Browning are credited with many fundamental discoveries, including the measurement l/d ratios, and the revelation of the beneficial effects of a high aspect …show more content…
Classification By Speed Range:- Wind tunnels are often denoted by the speed in the test section relative to the speed of sound. The ratio of the air speed to the speed of sound is called the Mach number. The tunnels are classified as
i. Subsonic (< 0.8) ii. Transonic (0.8 to 1.2) iii. Supersonic (1.2 to 5.0) iv. Hypersonic ( > 5.0)
For subsonic flows, the effect of compressibility is neglected and has smallest test section area.
For Transonic and Supersonic Flows, the effect of compressibility must be considered. In Supersonic Tunnels, the throat of the nozzle has the smallest c\s area and the test section area is chosen to achieve a desired Mach number in the test section.
For Hypersonic Flows, the effect of compressibility and additionally the chemical state of the gas is must be consider.
2. Classification By Tunnel Geometry:-
i. Open Return Tunnel:-
A Wind Tunnel which is open on both ends and draws air from the room into the test section is called open return tunnel. ii. Closed Return Tunnel:-
A Wind Tunnel that is closed and re-circulates the air through the test section is Closed Return tunnel iii. Blow down