Presentations of Surface Wind and Turbulence Using the Cathode-Ray Tube

Abstract

A combined analogue-digital technique is described for displaying the surface wind at various positions in the field, as vectors, correspondingly arranged, on the screen of a cathode-ray tube. Portable photoelectric anemometers and resolvers are used as sensors, and voltages representing two orthogonal wind velocity components are passed from each field position to the display equipment. Electrical filters are employed to reject the higher frequency fluctuations when time-smoothed vector winds are required and simple analogue averaging circuits are introduced for displaying the spatial-mean vector. Turbulence displays are obtained by the use of high-pass or band-pass filters which extract the time-mean flow and emphasize wind fluctuations in prescribed frequency ranges. Photographic recording of fluctuation vectors produce patterns of eddy structure and some examples, showing implied vortex-like motions, are presented. A scheme is suggested for displaying the vector winds at important points near the runways of an airfield, together with the spatial-mean vector, in the appropriate positions on the cathode-ray tube, and a method of presenting residual vectors by subtraction of the spatial mean is described. The techniques are further developed to represent on the tube, in graphical form, the variation of wind velocity with distance, and simulated three-dimensional oscillograms of wind fluctuations within the micro-scale range are shown.