Velocity Component Measurements by X Hot-wire Anemometry

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 V_eff. The authors demonstrate that these errors cannot be neglected, even at low turbulence intensity, if accurate flow measurements are required.