A Turbulence Indicator Utilizing the Diffusion of Heat

In cooperation with the National Advisory Committee for Aeronautics, the National Bureau of Standards for several years has been studying methods of determining the turbulence in wind tunnels, especially by the "hot-wire" method and the sphere method. This paper describes a third method.

The effect of turbulence upon the diffusion of heat from a small electrically heated wire in an air stream was investigated. The turbulence of the stream was introduced by a series of geometrically similar screens placed one at a time across the upstream section of the tunnel. With the wire set at various distances from the screens, curves of temperature distribution were obtained by traversing the heated wake at a distance of 2 inches behind the wire with a small thermocouple. A single relation was found to exist between the width of the wake at half maximum and distance in screen wire diameters from the several screens. The correlation of width at half maximum with percentage turbulence, as measured by the "hot-wire" method, could be represented approximately by a single curve.