No abstract

The authors deal with the use of X hot-wire probes for measurements of two velocity components. Using the effective velocity concept, four different analytical expressions for the yaw response of the hot wire signals have been considered. Using a set of reference calibration data the curve-fit accuracy of the four methods are first investigated. Then the related sum and difference signal analysis methods are compared and finally the velocity component errors caused by uncertainty in the value of the mean yaw angle are established.

The authors are concerned with the interpretation of the instantaneous signals from an X hot-wire probe used for velocity component measurements. A detailed calibration study was carried out to identify the correct velocity and yaw response of a typical plated X hot-wire probe. The calibration data identified an accurate calibration relationship for the X hot-wire probe, and enabled the development of a related look-up inversion method. This provided a reference for the assessment of the accuracy of common signal analysis methods. Using a step-by-step approach, the errors caused by the assumptions of constant values for the offset and exponent in a power law relationship were first identified. Then, the errors relating to the introduction of the concept of an effective velocity Veff and analysis in terms of Veff2 were determined and finally the errors in the sum and difference method based on Veff. The authors demonstrate that these errors cannot be neglected, even at low turbulence intensity, if accurate flow measurements are required.