The paper presents the results of the main physical processes that ensure the operation of hollow cathodes of vacuum plasma torches with the formation of high-enthalpy plasma inside the cavity. The interaction of the plasma with the inner surface of the cathode determines the temperature field of the hollow cathode and the distribution of heat fluxes in the vacuum discharge. The formation of the temperature field in the cathode body, in addition to temperature processes, is significantly influenced by the conditions of heat exchange between the cathode and the environment, the characteristics of the cathode material and its geometric dimensions. Studies of plasma emission spectra in the cathode cavity have shown that the appearance of spectrum lines depends on the excitation conditions and determines the energy limits of electrons accelerated in the cathode layer.
The paper presents the results of thermodynamic calculations and experimental studies of plasma processing of biomedical waste and fuel biomass, including waste from the woodworking industry and agriculture, which have shown the promise of using plasma-chemical technology for processing various wastes with production of combustible gas and inert mineral material. Comparison of the experimental results and calculations showed their satisfactory agreement. Both in calculations and in experiments, no harmful impurities were found in the products of plasma processing of the investigated wastes.
On November 30, 2022, an outstanding scientist in the field of thermal physics and thermal power engineering, Doctor of Technical Sciences, Professor, Academician of the Russian Academy of Sciences Alexander I. Leontiev passed away.
The paper describes the results of studying the influence of a free-stream disturbance localized in time and space on the structure of the wake behind a symmetric droplet-shaped airfoil in the range of angles of attack from -20° to +20°. It is demonstrated that the existence of such a disturbance leads to suppression of vortex formation at certain angles of attack. Ranges of angles of attack in which the wake structure remains unchanged are found.
This work is devoted to a numerical study of the influence of foreign-gas injection on the stability of compressible boundary layer on a concave surface. The stability calculation was carried out in the framework of the locally parallel linear stability theory. The results of calculations for the reference case without injection showed that Görtler vortices and the second Mack mode exhibited the highest growth rates at studied parameters. It is found that the injection of a heavy gas (with respect to the oncoming gas) leads to an increase in the rate of growth of Görtler vortices and the second Mack mode, whereas the injection of a light gas leads to a decreased rate of growth of these perturbations.
K.A. Dubrovin1,2, A.E. Zarvin2, V.V. Kalyada2, A.S. Yaskin2 1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia 2Novosibirsk State University, Novosibirsk, Russia
Keywords: gas dynamics, supersonic flows, argon, condensation process, clusters, visualization
Based on photometric measurements in an argon flow, the influence of large van der Waals clusters on the transverse dimensions of a supersonic under-expanded jet was revealed. In the range of average sizes of formed clusters 330 < 〈S〉 < 6200 part./clust., a model of corrections to the known gas-dynamic empirical dependences, formed in the absence of a condensed phase, was proposed to take into account the features of gas outflow from a supersonic nozzle under developed condensation. The possible reasons for the broadening of gas flows under conditions of developed condensation were established. The proposed correction model was tested in supersonic outflows of condensing gas on a number of supersonic conical nozzles.
An experimental study of the influence of the leading-edge bluntness radius of a plate on the response of boundary layer on this plate to an N-wave at Mach number M=2 was carried out. Three flat-plate models with leading-edge bluntness radii r = 0.05, 0.5, and 2.5 mm were used in the experiments. The oncoming-flow disturbances were created using a generator installed on the sidewall of the test section of the T-325 wind tunnel of ITAM, SB RAS. It is found that behind the N-wave in the oncoming flow there forms an extended region with an increased level of flow pulsations whose spectrum features amplitudes increased both in the low-frequency and in the high-frequency portion of the spectrum compared to the undisturbed free flow. It was shown that, under experimental conditions, the flow non-uniformity generated by the N-wave can exert a greater influence on the laminar-turbulent transition in the boundary layer of a flat plate with an increase in the leading-edge bluntness radius.
The development of instabilities in supersonic perfectly expanded jets exhausting from nozzles with square and rectangular cross sections into an ambient flow is studied based on the numerical solution of the Navier-Stokes equations. The simulations are performed for various Mach numbers of the jet and the ambient flow. The results of numerical calculations make it possible to identify qualitative and quantitative differences in instability development in cases with supersonic and subsonic air flows, as well as characteristic features of the flow for rectangular jets.
This work is a continuation of a cycle of research by the authors aimed at studying the laws of liquid hydrocarbon combustion under steam supply conditions as applied to the development of low-emission burners. When simulating numerically diesel fuel combustion, n-heptane (formula C7H16) is used as a one-component analogue. Reliable experimental data are required to verify the obtained results. In this work, for the first time, the combustion parameters of n-heptane are experimentally studied when it is sprayed with superheated steam in a new laboratory atmospheric burner with forced air supply to the gas generation chamber. The calculation results are compared with data on diesel fuel. The performed comparison shows that the characters of gas component dependences inside the flame for diesel and heptane differ. This is primarily due to the different densities, viscosities of fuels, their flammability and burning rate (depending, among other things, on the forced supply of air (oxidizer)). At that, a quantitative comparison shows that the values of gas components at the flame boundary are quite close to each other. The effect of ongoing physicochemical processes in the presence of steam (gasification, hydrocarbon splitting, combustible mixture dilution, formation of active OH radicals) on the composition of final combustion products is higher than the effect of fuel properties. It is shown that during the combustion of n-heptane atomized by a steam jet, all the main features characteristic of diesel combustion with steam supply are retained. High completeness of fuel combustion and low level of toxic emissions into the atmosphere are ensured, which satisfies the European standard EN:267. With an increase in the share of steam in the combustible mixture, the tendency to a CO and NOx decrease remains. The air flow control in the gas generation chamber of the burner allows further regulation of the level of toxic combustion products released into the atmosphere. The dynamics of dependences of CO and NOx emissions repeats for heptane and diesel with some local differences. Also, the paper analyzes the correctness of n-heptane applicability for the problems of numerical simulation of diesel combustion in a steam jet with the indicated assumptions.
For the first time, experimental studies were carried out on the effect of hydrogen combustion inside a supersonic (Ме= 2) flat-plate boundary layer on the laminar-turbulent transition in this flow. It was found in experiments that hydrogen injection (originating from the streamlined model) and its combustion in a certain sublayer partly stabilizes the layer flow. This result corresponds to the calculated data from S.A. Gaponov: it was shown that the heat supply into the supersonic boundary layer can deter the disturbance growth (i.e., facilitates the stabilization of the boundary layer stabilization). However, in general (compared to the non-combustion flow), the supersonic boundary layer is destabilized by combined hydrogen injection and fuel combustion. This means that the destabilizing effect of hydrogen injection prevails over the stabilizing effect of heat supply to the boundary layer.
