Evaluation of the K-Gill Propeller Vane

Abstract

Dynamic properties of the K-Gill propeller vane (k vane) are assessed from perturbation theory, wind tunnel, and field comparison experiments. Measurement errors for average wind speed are negligible. The dynamic response of the k vane can be described with a single response length that is the propeller?s distance constant at a 45° angle of attack. Measurement errors in longitudinal and vertical wind speed variances and the momentum flux due to propeller inertia can be described and corrected for as if the k vane were a simple first-order system. Standard spectra as well as spectra measured by the k vane itself can be used to calculate correction coefficients. In the latter case no information on atmospheric stability and boundary layer height is necessary. Transfer of lateral wind speed variance can be described as if the k vane were a damped harmonic oscillator. Measurement errors in lateral wind speed variance, however, are usually negligible because loss of high-frequency variance is compensated for by amplification of variance at the natural wavelength of the vane. The propeller?s distance constant and the vane?s natural wavelength derived from the field comparison experiments are both smaller than those derived from the wind tunnel experiments. When the k vane is used at elevated levels (z > 20 m), however, measurement errors become small and the exact values of the distance constant and the natural wavelength become insignificant. Parameters derived from the field experiments for the 35301 model are a response length of 2.9 m, a natural wavelength of 7.8 m, and a damping ratio of 0.49. When the k vane is used at levels higher than 20 m, the momentum flux lost due to instrument inertia will usually be less than 10%. This means that the k vane is a suitable sensor for flux measurements on tall masts.