Organized motions in a plane turbulent jet under controiled excitation.

The organised motion in the near field %f a plane turbulent jet under controlled excitation has been investigated experimentally by employing hot-wire techniques. Sinusoidal excitation is induced in the jet by a loudspeaker attached to the settling chamber and driven at the settling chamber cavity resonance fundamental frequency. The experiments were carried out at an exit pulsation amplitude of 1.4% of the exit velocity and cover a Strouhalnumber range 0.15-0.60 and a Reynoldsnumber range 8,000-31,600. The effect of the excitation on the mean velocity is much smaller than that on the turbulent field. But unlike in a circular jet, the wave fundamental amplitude is a small fraction bf the total rms turbulent velocity. The amplitude and phase distributions of the wave fundamental show that the disturbance which is induced as a symmetric mode remains symmetric at downstream stations. The wave fundamental reaches its maximum relative amplitude at the Strouhalnumber 0.18 at a streamwise distance at about 4 slit-widths downstream from the exit. The wave growth rate is much higher and the wave-length much smaller in the shear layer than on the centerline of the jet. The wave amplitude and phase data in the near field free shear layer agree with the spatial stability theory of Michalke.