Organized motions in a plane turbulent jet under controlled excitations.

The organized motion in the near field of a plane turbulent jet under controlled excitation has been investigated by employing hot-wire techniques. Sinusoidal excitation is induced in the jet by a loud-speaker 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 Strouhal number range 0.15-0.60 and a Reynolds number 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 of 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 Strouhal number 0.18 at a streamwise distance of 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. (A)