Acoustical Physics最新文献

Based on the hot-wire method for studying the fluctuations of compressible flows, the issues of determining the acoustic characteristics of the flow in the test sections of wind tunnels at transonic and supersonic speeds are considered. It is shown that for supersonic flows, in addition to the Mach waves described by Kovasznay, generated by stationary sources of disturbances on the walls of the test sections, and Mach waves generating the most intense fluctuations, distributed and moving in a supersonic turbulent boundary, described by Laufer, there may be Mach waves, the sources of which are sounds, as well as a turbulent boundary layer. Using the hot-wire approach, it is possible to determine the characteristics of each type of these waves and their source. It is also established that simple sound waves can be produced by the turbulent boundary layer and penetrate into the leading part from sources launched in the prechamber of the wind tunnel to the critical section of a Laval nozzle. In high-subsonic-speed wind tunnels, acoustic disturbances are produced from sound waves identified by intensity, direction and spectral composition using developed methods of thermal anemometry. The characteristics of acoustic disturbances (intensity, direction, location of sources) determined using the hot-wire method allow them to be purposefully preserved or reduced, or their influence on phenomena under investigation can be taken into account. The article was prepared based on the materials of the report at the 10th Russian conference “Computational Experiment in Aeroacoustics and Aerodynamics,” held September 16–21, 2024, in Svetlogorsk, Kaliningrad region (http://ceaa.imamod.ru/).

One of the areas of application of long-focus high-frequency ultrasound beams is visualization of the volume microstructure of materials. Visualization of the microstructure in acoustic microscopy in reflection mode is provided by recording signals during reflection or scattering of the ultrasound beam on the elements of the internal structure. Some of the elements can be acoustically rigid thin cylindrical scatterers. The radius of thin cylindrical elements is significantly smaller than the size of the focal spot of the probing beam, therefore, all thin elements of small diameter are displayed in acoustic images with the same size equal to the diameter of the focal spot. To estimate the sizes of thin cylindrical elements visible in the images, a theoretical approach is proposed that describes the formation of the amplitudes of output signals during the interaction of a focused ultrasound beam with thin cylindrical elements of the structure. The analytical description of the interaction takes into account the radius of the element and the sensitivity of the receiving acoustic system. Taking into account the parameters of the emitter/receiver and the geometry of the cylinder, the inverse problem of estimating the scatterer size depending on the received signal is solved. The theoretical approach is experimentally confirmed by visualization of thin polymer fibers using a scanning pulse acoustic microscope and acoustic lenses at frequencies of 50 and 200 MHz, forming focused beams of different geometries. Based on the results of comparison of experimental data and theoretical calculations, a conclusion is made about the applicability of the described analytical approach within the framework of assumptions and approximations for long-focus beams with a small-angle aperture when estimating the minimum dimensions of cylindrical scatterers visible in acoustic microscopy.

The article presents the results of a numerical investigation of the clocking, which is circumferential indexing of rotor or stator blade rows, and its effect on tonal noise for the first two booster stages of a turbofan engine low-pressure compressor. Calculations are performed for several relative positions of both rotor blade rows and stator blade rows. The considered computational model includes a row of fan rotor blades, rows of rotor blades, and rows of stator blades corresponding to the first two booster stages, as well as a row of inlet guide vanes of the booster. The stages have identical numbers of rotor blades and stator blades. The problem is to obtain the power of noise radiation and directivity patterns for the most intensive tones in operating mode (bar {N}) = 58%. The investigation is performed using a method of multistage turbomachine tonal noise calculation in the frequency domain. The method is capable of modeling a change in the relative position of blade rows without any manipulations with a computational grid. The results of calculations show that clocking of rotor blade rows can change the power of radiation from the inlet by 4 dB. Clocking of stator blade rows has a negligible influence on the total power of noise radiation from the inlet, though for some circumferential modes, the power can change by more than 5 dB. The article was prepared based on materials of a report at the 10th Russian conference “Computational Experiment in Aeroacoustics and Aerodynamics,” September 16–21, 2024, Svetlogorsk, Kaliningrad oblast, http://ceaa.imamod.ru/.

For an Euler–Bernoulli beam and a thin inextensible half-ring, it is shown that their Green’s function for normal forces and displacements can be zero in the presence of dissipative losses. The beam and half-ring are considered in two versions: with a simple support and movable seal at the ends. Solutions exist in wide frequency bands. For a half-ring with a movable seal, there are solutions for which the frequency derivative of the Green’s function is close to zero with a frequency-independent loss tangent. A vibration isolator in the form of a closed ring with four supports arranged at points corresponding to one of these solutions will have both theoretically infinite vibration isolation at one frequency and large vibration isolation in a wide band of neighboring frequencies.

To reveal the nature of artifacts in ultrasound images of human lungs (so-called B-lines), experimental phantoms were created consisting of a silicone layer for acoustic imitation of intercostal muscles, a layer formed with finely pored foam burn dressing imitating healthy or edematous lung tissue, a foam dressing fragment, a mandarin juice sac, and a drop of ultrasound gel imitating the structures of the lung tissue. Ultrasound images were recorded with a linear ultrasonic probe L7-4 connected to a Verasonics V-1 scanner. Additionally, an image of a mandarin juice sac located on the surface of the water was constructed using the synthetic aperture method with an Olympus focused piezoelectric transducer. The resulting echograms were compared with images recorded in clinical cases of pulmonary pathologies. It is shown that the appearance of B-lines is associated with the effects of multiple reverberation in liquid-filled structures imitating lung tissue, while their brightness and width on the echogram depend on the characteristic size of the internal structure of the phantom.