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Using the example of an integrated airframe, we performed a computational and experimental study of the possibility of using geometric diffraction theory (GDT) to calculate the sound diffraction when the airframe is replaced with simulating flat polygonal screen as pertains to the effectiveness of noise screening of aircraft power plants. We compared (1) impulse responses experimentally measured with maximum length sequences and the reciprocity theorem for both a three-dimensional model of the airframe and its plane model with (2) the responses calculated using GDT; the results showed good qualitative agreement for observation points in the geometric shadow zone and in the illuminated area, as well as quantitative coincidence in the frequency range characteristic of jet noise and the first harmonics of the blade passing frequency of a propeller or fan.

The article considers the problems of calculating the durability of orthotropic polygonal plates, described in the framework of the Kirchhoff theory and subjected to acoustic action with a wide spectrum, taking into account the effects of sound re-emission. A hybrid numerical-analytical method for solving the problem is proposed, based on the determination of the eigenmodes and vibration frequencies of the plate using the finite element method (FEM) with the subsequent calculation of the moments of the spectral density of rms stresses using the 5th order Gaussian quadratures. The article calculates the durability of a polygonal orthotropic fiberglass plate using four different methods (intersection method, Kowalewski method, Bolotin method and Reicher method) with a diffuse distribution of the sound field over the plate surface and random broadband acoustic exposure.

The paper presents the results of an experiment that uses the MLS technique to measure the impulse response when a signal passes through an air jet. The data are compared with the numerical simulation results obtained by solving the equation for sound propagation in a steady flow using a finite-difference method. It is shown that the longitudinal component of the flow causes drift and focusing of the signal.

Jet–flap interaction noise for a small-scale swept wing model of a trendsetter plane has been studied experimentally, with a double-stream nozzle installed nearby. The effect of the flap angle on the noise of jet–wing interaction has been analyzed. It has been discovered that the flap angle considerably affects the interaction noise in a wide frequency range in such a way that the noise intensity in each frequency band grows exponentially as the flap edge approaches the shear-layer boundary (on a logarithmic scale, this corresponds to linear scaling of the spectrum depending on the flap angle). The exponential noise reduction as the flap angle decreases agrees with the known theoretical simplified-configuration models that are based on the effect of interaction of the near field of instability wave with the edge. Not only does this agreement show that noise increase/reduction mechanism may be associated with similar processes, it also provides an effective tool for controlling the interaction noise.

An approach is proposed to describe the multipole structure of the sound field radiated as a turbulent jet streamlines a transverse circular cylinder of small diameter, which makes it possible to study the experimentally revealed effect of the dipole radiation shift. It is shown that different methods of acoustic measurements can lead to different determinations of the dipole radiation shift. It is demonstrated that to correctly describe the effect of the dipole radiation shift it is necessary to take into account the phase characteristics of different sources in the field of a turbulent flow; i.e., taking into account the state of distribution of the source is of fundamental importance for calculating the dipole radiation shift.

The method of product integration is applied to the vortex dynamics of two-dimensional incompressible viscous media. In the cases of both unbounded and bounded flows under the no-slip boundary condition, the analytic solutions of the Cauchy problem are obtained for the Helmholtz equation in the form of linear and nonlinear product integrals. The application of product integrals allows the generalization in a natural way of the vortex dynamics concept to the case of viscous flows. However, this new approach requires the reconsideration of some traditional notions of vortex dynamics. Two lengthscales are introduced in the form of a micro- and a macro-scale. Elementary ‘vortex objects’ are defined as two types of singular vortex filaments with equal but opposite intensities. The vorticity is considered as the macro-value proportional to the concentration of elementary vortex filaments inhabiting the micro-level. The vortex motion of a viscous medium is represented as the stochastic motion of an infinite set of elementary vortex filaments on the micro-level governed by the stochastic differential equations, where the stochastic velocity component of every filament simulates the viscous diffusion of vorticity, and the regular component is the macro-value induced according to the Biot–Savart law and simulates the convective transfer of vorticity.In flows with boundaries, the production of elementary vortex filaments at the boundary is introduced to satisfy the no-slip condition. This phenomenon is described by the application of the generalized Markov processes theory. The integral equation for the production intensity of elementary vortex filaments is derived and solved using the no-slip condition reformulated in terms of vorticity. Additional conditions on this intensity are determined to avoid the many-valuedness of the pressure in a multi-connected flow domain. This intensity depends on the vorticity in the flow and the boundary velocity at every time instant, together with boundary acceleration.As a result, the successive and accurate application of the product-integral method allows the study of vortex dynamics in a viscous fluid according to the concepts of Helmholtz and Kelvin.

Instability waves in the shear layer of turbulent jets are known to be a significant source of jet noise, which makes their suppression important for the aviation industry. In this study we apply plasma actuators in order to control instability waves in the shear layer of a turbulent air jet at atmospheric pressure. Three types of plasma actuators are studied: high-frequency dielectric barrier discharge, slipping surface discharge, and surface barrier corona discharge. Particle image velocimetry measurements of the shear layer demonstrate that the plasma actuators have control authority over instability waves and effectively suppress the instability waves artificially generated in the shear layer. It makes these actuators promising for application in active control systems for jet noise mitigation.