Study of the Position of Sound Sources in a Turbulent Jet Using Nozzles of Different Configurations

The aim of this work is to study the position of dominant sound sources in a small-scale turbulent jet using the beamforming method. Two nozzles of equivalent diameter and different geometric configurations (conical and chevron) were used to create different initial conditions for the outflow. Based on the analysis of the results obtained, it can be concluded that they are in good agreement with the well-known concepts of the physics of noise generation processes by turbulent jets: higher-frequency sources are generated by smaller-scale turbulent structures located closer to the nozzle edge, which is confirmed by the localization of high-frequency noise sources also closer to the nozzle edge. The chevron nozzles loosen the initial section of the jet, making it less short and thereby facilitating a faster displacement of noise sources to the nozzle edge, as seen when comparing localization maps for conical and chevron nozzles at the same frequencies. The results of localization were compared with the data obtained by other researchers. The results obtained were found to provide confidence in the use of acoustic beamforming to measure the location of the jet noise source with accuracy similar to other methods that have been used in the past.

Изотопно-селективное управление кластеризацией молекул SF-=SUB=-6-=/SUB=- и диссоциация ван-дер-ваальсовых кластеров (SF-=SUB=-6-=/SUB=-)-=SUB=-m-=/SUB=-Ar-=SUB=-n-=/SUB=- ИК лазерным излучением

We present the results of an investigation into the interaction of SF_6 molecules and clusters in a molecular beam with resonant IR laser radiation at different stages of the beam evolution along the axis of its propagation. The beam has been formed as a result of gas-dynamic expansion of a mixture of SF_6 with argon carrier gas during expansion from a pulsed nozzle. The experimental setup and the investigation method are described. It has been shown that selective vibrational excitation of SF_6 molecules with a specific sulfur isotope by a CO_2 laser near the nozzle edge causes suppression of the clustering process of these isotopic molecules. Selective IR excitation of clusters under the conditions of the formed cluster beam leads to isotopically selective dissociation of clusters. Depending on the experimental conditions including different distances of the irradiation zone of particles from the nozzle edge, the results of measuring the efficiency and selectivity of molecular clustering suppression and cluster dissociation processes are presented. It has been shown that both of these processes make it possible to achieve high selectivity values for the ^32S and ^34S sulfur isotopes. In the case in which the clustering of SF_6 molecules was selectively suppressed, selectivity values α ≥ 25–30 have been obtained. Upon selective dissociation of (SF_6)_2 dimers under similar expansion conditions of the gas mixture, selectivity values α ≥ 20–25 for ^32SF_6^32SF_6 dimers with respect to ^34SF_6^32SF_6 dimers have been obtained. Particular attention has been paid to measurements at a high dilution of SF_6 in argon under conditions of predominant formation of (SF_6)_ m Ar_ n mixed clusters. The potential of using studied processes as a basis for the technology of the laser isotope separation are discussed.

Дифференциальные характеристики поля течения перерасширенной газовой струи в окрестности кромки сопла

A parametric study of the features of the flow field of a plane and axisymmetric overexpanded ideal gas jet in the vicinity of the nozzle edge has been conducted over the entire theoretically admissible range of determining parameters (nozzle divergence angles, exhaust Mach numbers, jet incalculabilities, and gas adiabat indicators). The exhaust parameters that correspond to the extremes of the differential characteristics of a shockwave falling (descending) from the edge and the flow field behind it have been revealed. A significant difference in the character of changes in the characteristics of the shockwave and the flow field behind it depending on the type of symmetry of the gas jet has been found and studied.