measurement: a complete fan, or an impeller on a hydraulic installation. Two measuring tubes enable measurements of lower air currents (< 30,000 m3/h) as well as higher air currents (< 60,000 m3/h). The determination of the Q/h curve of the fan is one of the main objectives. To determine this curve (and to define other parameters) air technical, mechanical as well as electro technical data are measured: Air technical: Static pressure difference (Pa) Amount of moved air (m3/h) Average air speed (m/s) Specific efficiency (W/1000 m3/h) Efficiency Electro technical: Tension (V) Current (A) Cos φ Admitted power (W) fan / impeller Rotations per minute (RPM) The measurement can take place on the fan or in the application in which the fan is used. Wind engineering testing In wind engineering, wind tunnel tests are used to measure the velocity around, and forces or pressures upon structures. Very tall buildings, buildings with unusual or complicated shapes (such as a tall building with a parabolic or a hyperbolic shape), cable suspension bridges or cable stayed bridges are analyzed in specialized atmospheric boundary layer wind tunnels. These feature a long upwind section to accurately represent the wind speed and turbulence profile acting on the structure. Wind tunnel tests provide the necessary design pressure measurements in use of the dynamic analysis and control of tall buildings. See also Arsenal (Vienna), climatic wind tunnel centre used by the rail industry Automobile design Doriot Climatic Chambers, climatic wind tunnel centre operated by the United States military Frank Wattendorf Sting (fixture) Water tunnel, the hydrodynamics-oriented version of a wind tunnel List of wind tunnels References Further reading Jewel B. Barlow, William H. Rae, Jr., Allan Pope: Low speed wind tunnels testing (3rd ed.) External links Aerodynamics Articles containing video clips 19th-century introductions