Airborne Hot-Wire Measurements of the Small-Scale Structure of Atmospheric Turbulence

Abstract

An experimental investigation of small-scale atmospheric turbulence is presented. Airborne measurements were made in the vicinity of the meterological tower of Brookhaven National Laboratory. Hot-wire probes mounted on the right wing tip of a Cherokee aircraft were used. The anemometer signals were recorded on an analog tape recorder in the aircraft after differentiation and filtering; they were digitized in the laboratory with a high-speed analog-to-digital converter, and recorded on magnetic tape. All data were processed with an IBM-360. A fast Fourier transform program was used to compute the spectra. The average Kolmogoroff constant computed from the small-scale spectra was α = 2.0. The cospectra and quadrature spectra of the small-scale turbulence were virtually zero. The skewness and kurtosis of ∂ui/∂x (the derivative of a velocity vector with respect to the coordinate in the direction of aircraft heading) ranged from -0.03 to -0.50 and from 4.5 to 14, respectively, at Reynolds number (Rλ) from 2280 to 5330. The spectra of (∂ui/∂x)2 were found to exhibit a -0.3 power law in the inertial subrange. The probability distribution of (∂ui/∂x)2 was nearly a straight line in log-normal coordinates.