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.
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.
The control of the deuterium–tritium (DT) fuel isotopic ratio has to ensure the best performance of the ITER thermonuclear fusion reactor. The diagnostic system described in this paper allows the ...measurement of this ratio analyzing the hydrogen isotope fluxes (performing neutral particle analysis (NPA)). The development and supply of the NPA diagnostics for ITER was delegated to the Russian Federation. The diagnostics is being developed at the Ioffe Institute. The system consists of two analyzers, viz., LENPA (Low Energy Neutral Particle Analyzer) with 10–200 keV energy range and HENPA (High Energy Neutral Particle Analyzer) with 0.1–4.0MeV energy range. Simultaneous operation of both analyzers in different energy ranges enables researchers to measure the DT fuel ratio both in the central burning plasma (thermonuclear burn zone) and at the edge as well. When developing the diagnostic complex, it was necessary to account for the impact of several factors: high levels of neutron and gamma radiation, the direct vacuum connection to the ITER vessel, implying high tritium containment, strict requirements on reliability of all units and mechanisms, and the limited space available for accommodation of the diagnostic hardware at the ITER tokamak. The paper describes the design of the diagnostic complex and the engineering solutions that make it possible to conduct measurements under tokamak reactor conditions. The proposed engineering solutions provide a safe—with respect to thermal and mechanical loads—common vacuum channel for hydrogen isotope atoms to pass to the analyzers; ensure efficient shielding of the analyzers from the ITER stray magnetic field (up to 1 kG); provide the remote control of the NPA diagnostic complex, in particular, connection/disconnection of the NPA vacuum beamline from the ITER vessel; meet the ITER radiation safety requirements; and ensure measurements of the fuel isotopic ratio under high levels of neutron and gamma radiation.
A neutron collimator is developed to attenuate the neutron flux and reduce the residual induced activity in the interportal space of the diagnostic system of neutral particle analyzers of the ITER ...tokamak reactor. The collimator is installed in the port plug of the ITER vacuum vessel in front of an inlet to the vacuum pipeline of the diagnostic system. The collimator design has a cellular structure with 80% transparency for the neutral atom beam that goes out of the plasma and is recorded by the analyzers. However, because of increased scattering of neutrons in the collimator, their flux in the interportal room in the service zone of diagnostic systems of equatorial port no. 11 is significantly reduced and allows the equivalent dose rate in this zone to be decreased by several times. Thermal analysis showed that, during the reactor operation in modes with generation of the maximum power of 500 MW, the plasma radiation will cause the heating of the collimating grid to a temperature not exceeding 250°C, which makes it possible to select the stainless steel (316L(N)-ITER grade) as a material for manufacturing the collimator. In this case the cyclic strength of the collimator meets the ITER requirements, and it can be used without replacement during the entire deuterium-tritium experiment of the tokamak reactor.
The possibilities of using active neutral particle diagnostics for measuring local ion temperatures and isotopic ratio of deuterium-tritium plasma at the tokamak with reactor technologies are ...considered. Options for positioning the neutral particle analyzer relative to the diagnostic injector are presented. The fluxes of deuterium and tritium atoms escaping out of plasma were simulated in a wide range of plasma densities and temperatures. It is shown that the neutral particle analyzer active diagnostics will make it possible to measure the plasma parameters mentioned with the spatial and time resolutions of ~14 cm and ~0.01–0.1 s, respectively.
The results of experiments are described, which were performed at the Globus-M2 tokamak and aimed at studying the fast ion loss at the outer tokamak wall due to fast ions interaction with the ...toroidal Alfvén eigenmodes. The local heating of carbon tiles was experimentally measured, and the corresponding heat flux was calculated. It was shown how simulations of the lost particle orbits can explain the characteristic features of the spatial map of wall heating. The flux of lost fast particles onto the wall was studied as a function of the instability amplitude. It has been demonstrated that the simulations predict similar dependence of the fast ion flux on the instability amplitude and also correlate its nature to the peculiarities of fast ions spatial distribution.
