FLOW-FIELD CHARACTERISTICS IN A TURBULENT JET: EXPERIMENTAL DETERMINATION OF SOUND SOURCE LOCATIONS

摘要

On the basis of known experimental data, the general concepts of flow-field structure in turbulent subsonic axisymmetric jets are discussed. The complicated processes of turbulent mixing such as unsteady flow, turbulence intermittence, and interference of different regions of the flow are illustrated. Special attention is paid to the existence of a thin region of "turbulent fluid" within the mixing layer. Unsteady motion of this region forms the general structure of the mixing layer. Results of our experimental investigation of flow structure and pulsation characteristics of turbulent jets in the jet initial region are presented. These experimental data are compared to the results of measuring pressure pulsations outside the jet flow. A certain interconnection of characteristic dimensions of dynamic inhomogeneities (vortices) with a frequency value is shown to take place in the locations of sound sources of a certain frequency. The transverse dimension of vortex coincides with the thickness of the turbulent fluid layer. On the basis of this fact, and taking into consideration the analysis of the known data, it is concluded that the acoustic wave generation can be attributed to the unsteady motion of the turbulent fluid layer.