On the rotating, slanted, hot-wire technique

The purpose of this paper is to convey information and experience gained in the use of a rotating slanted hot-wire probe to measure the complete Reynolds stress tensor and the mean velocity vector. The technique is limited to nearly one-dimensional flows with turbulence intensities less than 10%. This paper extends the description of the method and discusses potential problems and difficulties one my encounter with this technique. In particular, the use of an appropriate least-squares technique (singular value decomposition) is suggested as this gives a more accurate fitting than simply using a matrix inversion of the normal equations. The covariance matrix is used to determine the slant angle and rotation positions of the probe most favorable to the least squares fitting and provides a measure of the uncertainties in the solution for the Reynolds stresses. The technique presented was used to determine the anisotropy of a turbulent flow with no mean shear. The results compare well with cross-wire measurements.