On the error-sensitivity of calibration procedures for normal hot-wire probes

The results of an investigation on the sensitivity of various hot-wire calibration procedures to errors in probe positioning are described. The analysis was carried out by means of a computer simulation procedure and regarded, in particular, methods for the evaluation of the direction sensitivity coefficients. It is shown that the classical calibration procedures are characterized by a high sensitivity to experimental errors, and this may explain both the large scatter usually found in the values of the direction sensitivity coefficients and, at least partially, their variation with yaw and pitch angle. New calibration procedures are also described which appear to be significantly less sensitive to errors in probe positioning and velocity setting. The practical application of the various procedures to the calibration of a typical commercial probe seems to confirm the results of the computer simulation analysis.