An X-array hot-wire technique for heated turbulent flows of low velocity

A calibration and signal analysis technique has been developed for a multiple-sensor probe, comprising an X-array hot wire and a cold wire, to account for the effects of both yaw angle and temperature on the instantaneous output signals of the X-wire. The technique assumes the response equation first proposed by Collis and Williams (1959) and involves a series of velocity calibrations at different flow angles producing independent sets of the calibration coefficients which thus describe the yaw angle dependence. The complexity of the calibration is comparable to variable angle methods which use a look-up table approach, but the present technique offers complete separation of the temperature and velocity effects on the X-wire signals over a large range of temperature without requiring additional calibration. The instantaneous velocity vector is unambiguously resolved within the full 90 degrees included angle between the sensors of a standard gold-plated X-wire, and in addition, the technique identifies the occurrence of rectification errors. The signal analysis technique is verified in the calibration apparatus and has been applied successfully in an inclined heated plane jet of low mean velocity.