EVALUATION OF THE K-GILL PROPELLER VANE

Dynamic properties of the K-GIII propeller vane (k vane) are assessed from perturbation theory, wind tunnel, and field comparison experiment s. Measurement errors for average wind speed are negligible. The dynam ic response of the k vane can be described with a single response leng th that is the propeller's distance constant at a 45 degrees angle of attack. Measurement errors in longitudinal and vertical wind speed var iances and the momentum fur due to propeller inertia can be described and corrected for as if the k vane were a simple first-order system. S tandard spectra as well as spectra measured by the k vane itself can b e used to calculate correction coefficients. In the latter case no inf ormation on atmospheric stability and boundary layer height is necessa ry. Transfer of lateral wind speed variance can be described as if the k vane were a damped harmonic oscillator. Measurement errors in later al wind speed variance, however, are usually negligible because loss o f high-frequency variance is compensated for by amplification of varia nce at the natural wavelength of the vane. The propeller's distance co nstant and the vane's natural wavelength derived from the field compar ison experiments are both smaller than those derived from the wind tun nel 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. Par ameters derived from the field experiments for the 35301 model are a r esponse 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 tha n 10%. This means that the k vane is a suitable sensor for flux measur ements on tall masts.