In many technical units pressure of gaseous fluids is reduced in turbulent jets with high subsonic velocities. In addition to broadband noise of the jets individual frequencies are sometimes observed. Those frequencies are caused by formation of periodic vortex structures in the jet. In some cases vortex formation can be influenced by sound waves which are emitted upstream of the discontinuity.
This effect is been investigated experimentally at velocities between Ma = 0.3 and Ma = 0.9 in several nozzles. The effect of the excitation on the turbulence in the jet is been measured by means of a dynamic pressure probe. It is shown that the turbulent vortex formation is influenced by the sound wave over a wide frequency range. A visualization of the density field shows regular vortex structures in the jet.
The noise emission is simultaneously investigated with condenser microphones. In addition to the frequency peak at the excitation frequency an increase of the broadband jet noise level can be observed.