Initial turbulence effect on jet evolution with and without tonal excitation

The effect of the initial turbulence level on the development of an axisymmetric jet was experimentally investigated. The turbulence intensity at the jet exit was varied, over the range 0.15%–5%, by using screens and grids placed upstream of an 8.8 cm diam nozzle. Top‐hat initial mean velocity profiles with approximately identical boundary layer states were ensured in all cases; the turbulence was homogeneous and the spectra were broadband. It was found, contrary to earlier reports, that the natural jet evolution remained essentially unchanged for varying initial turbulence intensities. The response of the jet to single frequency, plane wave excitation was then studied over the full range of initial turbulence intensities. It was found that for even the highest turbulence (5%), the jet was quite excitable and could be influenced measurably by a tone of small amplitude. However, the jet ‘‘excitability,’’ as assessed from the variations of the mean velocity as well as the total and fundamental rms amplitude...