No abstract

The main goal of the paper is to assess the contribution of large-scale vortices to the noise of the subsonic turbulent jet (M = 0.35, Re = 3.2•10 5) in the selected frequency bands (Sh~0.2-0.45). The mechanism of sound radiation according to which a separate vortex structures itself can be a significant sound source is considered. Vortex core eigen-modes are responsible for noise radiation according to this mechanism. The work is subdivided on three coupling items: (i) theoretical investigation of noise radiation of separate vortex ring (especially little-known octupole contribution to sound radiation), (ii) visualization of large vortices in excited jet and (iii) experimental investigation of turbulent jet noise (subsonic jet with velocity 120m/s excited at 2000Hz) decomposed on the separate azimuthal components with the help of azimuthal decomposition technique (ADT). On the final stage the careful comparison of these results gives the quantitative assessment of the contribution of vortex rings to the jet noise in a tone-excited turbulent jet under consideration.

We study experimentally how plasma actuators operating on the basis of surface barrier high fre quency discharge affect jet noise characteristics. The results of investigations of air jets (100-200 m/s) have demonstrated that the studied plasma actuators have control authority over the noise characteristics of these jets. An actuator's effect on the jet in the applied configuration is related to acoustic discharge excitation and to a large extent is similar to the well known Vlasov-Ginevsky effect. It has been shown that jet excitation in the case of St ~ 0.5 using the barrier discharge plasma actuator leads to broadband amplification of jet sound radiation. The jet excitation in the case of St > 2 leads to broadband noise reduction if the action is sufficiently intensive.

It is generally accepted that one of the main sources of acoustic radiation from a supersonic jet is due to spatial instability wave packets propagating downstream within the jet. This approach has enabled us to explain and predict the principal features of sound radiated by a supersonic jet with a circular nozzle. The aim of this present work is to generalize such an approach to jets with a circular nozzle deformed into a weakly corrugated (s-lobed) shape. This leads to the presence of two additional parameters, the lobe number (an integer) characterizing the corrugation wavelength and the corrugation amplitude. Their presence can be shown to lead to a resonant coupling between different instability waves which, in turn, can both intensify and suppress the aerodynamic noise. The assumption of a small corrugation amplitude allows us to consider the problem analytically using disturbance theory methods. The structure of the eigen-oscillations is determined at leading orders, where it is shown that differing azimuthal harmonics are coupled over a wide range of frequencies. The result of such couplings on the radiated sound is significant, even for a small corrugation amplitude. The above suggests that the effect of mode coupling, due to nozzle corrugation, could be used as a tool for noise control in supersonic jets.

Theoretical and an experimental investigations of jet noise modification are carried out for the jet issuing in the vicinity of the wing. The effect of interaction between instability waves in the jet and flap solid boundaries has been studied. Expermental investigation of jet noise from a dual flow nozzles near a wing provides assessment of several parameters (chevrons on primary and secondary nozzles, distance between the trailing edge of the flap and the nozzle, distance between the plane of the wing to the jet axis, presence of the pylon, etc.) on jet noise installation effect.