Experimental study of free turbulent jet

Abstract

In the article the results of studying the dynamics of the development of a free turbulent jet flowing out of a square-shaped nozzle are presented. The studies were conducted both in the presence of external influence, and without influence. The average and pulsation values of the velocity were measured using a thermoanometer, and the turbulence level was analyzed. Dimensionless temperature profiles on the axis of the free jet emerging from the nozzle were studied. To study the vortex structure of the flow, the
method of instantaneous velocity pulsation measured by a hot-wire anemometer and recorded on an oscilloscope screen was used. Average and pulsation values of speed, level of turbulence (intensity of turbulence) were measured using a hot-wire anemometer. Based on the analysis of the oscillograms of instantaneous pulsations, the development frequencies were calculated for the appearance of large-scale first-order eddies and for their distance from the nozzle. The analysis of the oscillograms of the transverse instantaneous pulsation showed that the speed fluctuations have certain frequencies. These oscillations of the velocity, which manifest themselves in the initial part, coincide exactly with the frequencies of large-scale discrete vortices formed in the free boundary layer. Since downstream, with distance from the nozzle exit section, large-scale first-order eddies interact with each other and, as a result of an increase, this leads to the appearance of high-amplitude low-frequency oscillations of velocity.