Real-time measurements of turbulence quantities with a triple hot-wire system.

This paper describes a technique for measuring turbulence quantities in highly turbulentflows whose mean-flow direction is not well known. Three orthogonal hot-wire anemometers are used, with individual linearizers. Their signals are simultaneously processed, in realtime, by a network of high-speed analog devices. Instantaneous values of u,v, and w (velocity components in laboratory coordinates) are calculated, using the directional characteristics of each wire and its orientation within the test tunnel. The instantaneous velocity signals can be either processed by a digital computer or introduced into a second analog network which separates the signals into mean and fluctuating components amd forms any desired dou ble or triple correlation, again in real time. Electrical qualification tests of the analog system have shown the output amplitude to be independent of frequency to within 0.1% up to 20 kHz and the phase shift between components to be less than 1% up to 7kHz. Fluid dynamic qualification tests were conducted in a two-dimensional channel flow whose mean and turbulence quantities are believed to be well known. A standard triple-wire probe was used and traverses made with various combinations of pitch and roll on the probe. Progress is being made in the development of a compact triple-wire probe, which is expected to improve the near-wall behaviour. (A)