Wave Propagation on Turbulent Jets

Abstract

Results of experiments involving the propagation of acoustically generated waves on turbulent plane jets are presented. The jets are produced by a perspex reconstruction of an organ pipe flue and their behaviour is shown to conform to the predictions of similarity and self-preservation; i.e. the jet velocity V"' x-1/2 and the jet-width is proportional to x, where xis the distance from the slit. Thus they are fully turbulent and, as a consequence, well behaved and reproducible. The measured wave velocities for frequencies between 200 Hz and 1200 Hz and slit-widths between 0.5 mm and 1.0 mm are compared with similar mea$urements on laminar jets. However, the stable nature of the turbulent jet allows much higher blowing pressures, up to 1500 Pa, to be used. The wave velocities u for the turbulent jet vary as x-1/2 and so the ratio of the ·wave velocity to the jet centre-velocity is constant along the jet. This ratio is closely equal to 0.5 except for small values of the effiux velocity and slit-width wh3re it rises to 0.6.