In this paper, we analyze the acoustic analogy method in relation to the sound radiation of a turbulent subsonic jet. This method of describing aerodynamic sound generation by turbulent flows is ...based on the use of a linear propagation operator with a random source on the right side. The main problem here is the choice of an effective way to separate the left side of the equation, which is responsible for the propagation of sound waves, and the right part, which is responsible for sound generation, so that the noise calculation result corresponds to experimental data and physical ideas about noise generation by turbulence. One of the unsolved problems of the approach, which is common in most acoustic analogies, is the problem of the so-called “shear noise” associated with the excitation of shear flow disturbances by sources and the additional contribution of these disturbances to sound radiation. It is still unclear whether the shear component of the noise is a reflection of real physical processes or is associated with the transformation of equations and inaccurate modeling of sources. Here, within the framework of the problem formulated above, we consider an acoustic analogy, in which the linearized Euler equations are used as the propagation operator. In this description, the propagation operator contains vortex modes, which leads to the appearance of a shear noise component that arises due to the pumping of vortex disturbances by the sources. When modeling sound sources, hypotheses about the quadrupole nature isotropy of sound sources, as well as the spatial uncorrelation of sound source production, are used. To validate the model, the measurement data of the sound emission of the jet using the azimuthal decomposition method are used. The comparison of the model and experiment indicates the absence of a shear component in the jet noise. This makes it possible to conclude that the idea of pumping linear vortex perturbations of the mean flow by nonlinear turbulent pulsations that is used in the considered acoustic analogy does not correspond to the real mechanism of noise generation by a turbulent jet. Possible causes of the discrepancy between the model and the data of acoustic measurements are analyzed. Possible ways of solving this problem, which make it possible to effectively separate the left side of the equation that is responsible for the propagation of sound waves and the right nonlinear part that is responsible for sound generation are considered.
Abstract
Active NPA measurements of the fast ion distribution using the neutral beam as an additional charge exchange target are discussed. Expressions for the calculation of the NPA signal based on ...the fast ion distribution and for the reconstruction of the fast ion distribution from the NPA signal are provided. Demonstration of the described approach is carried out on the Globus-M2 spherical tokamak, where a scanning system for the NPAs was recently installed. Main features of the active NPA application on Globus-M2 are considered. The energy and spatial distributions of fast deuterium ions at dedicated pitch angles are obtained and compared with the calculated ones. Key traits of the obtained distributions are considered and explained.
The behaviour of the fast particle population during 18 keV hydrogen and 26 keV deuterium neutral beam injection in deuterium plasmas is investigated. Experiments reveal large fast ion losses. The ...experimental results are confirmed using different types of modelling: simulation using the NUBEAM module, solution of the Boltzmann kinetic equation and solution of the 3D fast ion tracking algorithm. The dynamics of the energetic particle redistribution and losses during sawtooth oscillation and toroidal Alfvén eigenmodes are studied. A method to decrease fast ion losses under the current conditions (0.4 T, 0.2 MA) is shown. The influence of the plasma parameters on the energetic ion confinement rate is investigated. Modelling for the Globus-M2 conditions (1 T, 0.5 MA) is performed.
Abstract
The NPA based diagnostic complex in ITER consists of four diagnostics: the neutral particle analyzers, the diamond neutral particle spectrometer, the gamma-ray spectrometer, and the neutron ...spectrometer. The diagnostics are located in equatorial port #11 and share the same vacuum channel. The present paper considers the physical basis of the diagnostic complex and its measurement capabilities in ITER. In addition, the design of the complex and the engineering solutions implemented to meet the ITER requirements are described.
In this paper, we study the mechanism of noise generation in a turbulent jet using the acoustic analogy method. The aim of this study is to develop a sound source model that does not contain the ...so-called shear noise component. This condition was formulated earlier as a result of the analysis of multi-microphone acoustic measurements of the jet, which showed that the acoustic analogies that take into account shear noise disagree with the experimental data. The model proposed here is based on the separation of acoustic and hydrodynamic variables and the use of a propagation operator that does not contain hydrodynamic degrees of freedom. This approach makes it possible to eliminate naturally the shear component in the sound emission and achieve good agreement with the acoustic measurement data. A sound source is simulated under the assumptions of quadrupole and isotropy of the pulsations responsible for sound radiation. The simulation results are compared with experimental data on the directivity of the main azimuthal harmonics of the sound radiation of the jet at a velocity of 120 m/s. The obtained results provide an important contribution to understanding the nature of sound-emitting turbulence in shear flows.
The applicability of neutral particle diagnostics for studying plasma parameters and additional methods of heating in the Tokamak with Reactor Technologies is analyzed. Options for the arrangement of ...diagnostic equipment, which includes three analyzers of charge-exchange atoms (neutral particle analyzers) for different energy ranges of recorded atomic fluxes, are given. It is shown that the diagnostic complex of analyzers makes it possible to measure the distribution functions of plasma thermal ions and to obtain information on the isotopic ratio of the main plasma ion component in the deuterium–tritium mode of facility operation. In addition, the proposed geometry of the analyzer arrangement makes it possible to measure the energy distribution of fast ions, which arise during neutral beam injection and ion cyclotron heating of plasma.
A scheme of a multichannel time-of-flight atomic analyzer with an electrostatic deflection system that provides two-dimensional focusing of the ion beam in the transverse direction is described. A ...thin carbon film with a thickness of 100 Å is used to ionize the incoming flow of atoms. The results of numerical simulation of the main parameters of the analyzer, such as the energy values in the channels, their energy resolution, and permeability, are given. An example of the possible use of such an atomic analyzer for measuring the energy distribution function of thermal plasma ions and fast ions of heating beams in the deuterium–tritium operating regime of the TRT facility is considered. The efficiency of radiation background suppression in the analyzer detection system by the coincidence circuit has been analyzed.
A two-dimensional system consisting of a circular cylinder placed in a circulating flow of an inviscid incompressible fluid with variable vorticity is considered. The processes in the critical layers ...of vortex flows (the region in which the phase velocity of disturbances coincides with the velocity of the mean flow) are investigated using the example of a problem with an exact analytical solution. Previously, for such a system, the discrete part of the spectrum was considered and described; i.e., individual natural oscillations are obtained and it is shown that, in a certain range of parameters, the system exhibits shear instability. The features of the system dynamics related to a continuous spectrum are considered. For this purpose, the initial problem is solved, and an analysis of the growth of large vorticity disturbances in the vicinity of the critical layer from a state with smooth initial conditions is made.
The paper proposes to describe the dynamics of perturbations of compressible ideal gas flows in the formalism of Lagrangian mechanics. The key point is the choice of generalized coordinates that most ...naturally describe the system dynamics. The proposed choice of main variables leads to the Lagrange equations, which correspond to the displacement field equation and convective wave equation for the scalar potential. This approach yields the acoustic energy balance equation via the first variations of the variables for the flows with nonzero vorticity. The results can be used for energy analysis of the sound emission for flows with localized vortices, jet flows, and duct flows.
