No abstract

No abstract

Free turbulent jets produce disturbances in the ambient medium which at a certain distance from the jet are perceived as sound waves. These disturbances are due to unsteady fluctuating motion of the medium in the jet flow (intermittance). The origin of the acoustic disturbances can be attributed to turbulence intermittance. Due to lowered pressure in the movable dynamic inhomogeneities of the turbulent fluid, they induce air ejection by the jet, which turns out to be fluctuating in nature, since the turbulent fluid flow is unsteady. The proposed mechanism of the generation of acoustic disturbances accompanying turbulent jet propagation is verified in numerical and experimental studies; in particular, the formation of acoustic fluctuations in the half-space over a surface which contains an embedded fluctuating finite-size sink is considered on the basis of the numerical solution of the unsteady Reynolds equations. From the results of the numerical experiment performed using large eddy simulation the fluctuating characteristics of the flow in a swirling jet and the direction of the disturbance energy flux in the ambient medium are determined. An experimental investigation of the disturbances produced by a strongly swirling jet is also carried out. Fig. 8. Profiles of the mean velocity components at a distance X = 40 mm from the nozzle exit; (1) IDDES and (2) experiment. FLUID DYNAMICS Vol. 50 No. 3 2015 FLUID DYNAMICS Vol. 50 No. 3 2015 386 KRASHENINNIKOV et al.According to the data obtained for the swirling jet the flux of the sound fluctuation energy is formed in the ejected flow, starting from the region boundary, on which ⟨p ′ v ′ ⟩ = 0. It increases with decrease in the phase difference between the velocity and pressure fluctuations, upon transformation of the fluctuating motion energy in the ejected flow to the acoustic energy. In the case of free turbulent jets the process is apparently analogous, since, according to [7,8], the ejection effects are similar in both cases.The study was carried out with the support of the Russian Foundation for Basic

No abstract

No abstract