In high-pressure gas-jet emitters, the source of sound energy is kinetic energy of gas jet at supercritical pressure ratios between the working pressure and the atmospheric pressure. Under certain conditions, interaction of a supersonic jet with the resonator is accompanied by powerful self-excited oscillating process with the generation of acoustic waves into the environment and cavity resonator. A model of a self-excited oscillating process arising from the interaction of non-isobaric jet with semi-closed cylindrical cavities, allowing to distinguish typical elements of gas-dynamic structure of the forming flow, is considered. The physical pattern of the flow in the cavity of gas-jet emitter is discussed, and a study of the dependence of the characteristics of the self-excited oscillating process on the gas-dynamic and geometric parameters is performed.
In this paper the first thirty-two axisymmetric modes for steady-periodic waves in viscous compressible liquids contained in rigid, impermeable, circular tubes are calculated. These results end long speculation over the effects of viscosity on guided acoustic waves. Sixteen of the modes belong to a family of rotation-dominated modes whose existence was previously unknown. The thirty-two modes were computed for a wide range of frequencies, viscosities and wave-lengths.The modes were found through the use of the method of eigenvalleys, which also led to the discovery of backward-propagating waves, an exact analytical expression for the zeroth rotational mode eigenvalue, definitive boundaries between low and intermediate frequencies and between intermediate and high frequencies, and a new type of boundary layer, called a dilatational boundary layer.
Acoustic logging while drilling (LWD) can extract P-wave and S-wave information from the formation. However, the transmission of the collar wave propagated directly from the emitter to the receiver may interfere with the P-wave and S-wave and affect the extraction of formation information. Therefore, it is necessary to design a suitable acoustic isolator between the transmitter and the receiver to attenuate the drill waves. The commonly used acoustic LWD isolator is that the outer surface of the drill collar is evenly grooved to attenuate the collar wave. However, there are still disadvantages such as the lack of mechanical strength of the evenly grooved acoustic insulators and the ability to extract clean longitudinal wave under certain circumstances. Therefore, there is an urgent requirement to design a new type of acoustic LWD isolator with sufficient strength and acoustic insulation requirements. In recent years, spoof surface acoustic waves (SSAWs) generated by periodic corrugated surface rigid plates have attracted the attention of many researchers, who can spatially separate the surface waves to attenuate acoustic waves. In this paper, a new type of acoustic LWD insulator based on SAW space separation structure is proposed. The finite element software ANSYS is used for acoustic analysis.
Акустические характеристики автоколебательного процесса, возникающего при взаимодействии сверхзвуковой недорасширенной струи с цилиндрической полостью