The R.A.E. 4-ft x 3-ft experimental low-turbulence wind tunnel. Part II measurements of turbulence intensity and noise in the working-section

Abstract

Measurements are given of the turbulence in the working-section together with measurements of the noise. With all the screens fitted in the tunnel, the intensities of lateral components are of the same order as the longitudinal component and range from about 0.01 per cent to 0.03 per cent of the mean speed. Frequency analyses have shown the longitudinal components to consist of fan frequencies and a low-frequency contribution at about 5 to 10 c.p.s. The lateral components consist almost entirely of a similar low-frequency contribution. With all the screens in the tunnel the low level of turbulence is confined to a restricted area near the centre of the tunnel with flashes of high-intensity turbulence spreading a considerable distance from the walls. Noise measurements with the hot-wire microphone in the middle of the working-section showed that above a tunnel speed of 150 ft/sec the longitudinal component consisted mainly of noise. Some measurements were also made with the hot-wire microphone in the turbulent boundary layer on the walls.