Том 56, № 6 (2018)

In the present paper we recall the classical Taylor–Green vortex turbulent decay in terms of isotropic turbulence theory. In particular, we calculate the spectral turbulent kinetic energy transfer \(T(k)\) and the spectral flux \({{\Pi }_{E}}(k)\) basing on the longitudinal triple correlation function (the two-point third-order velocity moment). These functions can be also obtained in other way via the generalized Karman–Howarth equation for homogeneous turbulence using integral of triple modes interaction. In both cases, the spectral transfer and the flux appear to be different from the characteristics of isotropic or homogeneous turbulence due to the peculiarities of the problem statement. The results obtained outline the range of obstacles associated with the construction of spectral turbulent models in complex heat and mass transfer problems arising due to periodicity effects, closeness of integral turbulent scales to modeling box size and lack of spectral resolution.

The results of numerical modeling of the gasdynamic interaction between a highly inertial particle and the shock layer are presented. The evolution of the shock-wave and vortex flow pattern that appears when a particle reflected from a streamlined surface passes through a shock wave is analyzed. It is shown that an essential part is played in the formation of a wave flow pattern by a toroidal vortex, which results in the “nonviscous” detachment of the near-axis incident flow from the symmetry axis and its further interaction with the outer flow and the body surface. It is indicated that an intensive pressure wave passes along the streamlined surface, thus creating the conditions for the intensification of convective heat transfer.

The conversion of diesel engines into gas engines is a promising way to solve environmental and energy problems. In this paper, we first posed and solved the problem of nonstationary local heat transfer in a diesel combustion chamber converted to run on natural gas and hydrogen. The main characteristics of the working process and local heat transfer in the converted engines with respect to the used alternative fuel are studied by 3D modeling of the internal cylindrical processes and the thermal state of the pistons. The measurements of nonstationary pressure in the cylinder and the local temperatures of the piston on a running engine are used to verify the mathematical models. It is established that the features of the working process, due to the transition to forced ignition of a homogeneous combustible mixture, significantly affect the magnitude and nature of the change and the distribution of local heat loads on the piston surface. Based on comparative analysis of the thermal state of the pistons of converted engines, practical recommendations are issued to ensure the efficient conversion of diesel engines to operate on gas fuels.

The chemical composition of bio-oil obtained from Arthrospira platensis biomass via hydrothermal liquefaction at 240–330°C has been studied with an elemental analysis and Fourier transform ultrahigh resolution mass spectrometry with ionic cyclotron resonance. An increase in temperature leads to an increased bio-oil yield, decreased oxygen, and an increase in the amount of carbon and nitrogen. The weighted Kendrick mass defect histogram showed for the first time that the main nitrogen-containing and oxygen-containing compounds are ON, O₂N₃, O₃N₂, ON₂, N, and N₂. The character of the change in their relative amount in bio-oil with a temperature change is also revealed. The Venn diagram shows the intersection of the sets of molecular formulas found in bio-oil samples obtained at different temperatures. The results may be used to optimize the hydrothermal liquefaction of microalgae and their subsequent processing into motor fuel.

Experimental studies of the heat release processes in the apokamp discharge were carried out via the plotting of intensity charts. The procedure was verified with measurement techniques similar to those used in the operation of a disappearing filament pyrometer. A criterion was formulated for its applicability for the study of apokamp discharge in air. The intensity charts obtained at different stages of the formation of discharge confirm the need for gas heating near the discharge channel to form streamers.

The paper deals with single-phase AC plasma torches with rod electrodes made of iron-copper composite material, with air as the plasma-forming gas and an life time of ~200 h. The construction peculiarities of this type of plasma torch and its power-supply systems is described. The experimental results, in particular, the current-voltage and the voltage-flow rate characteristics of the plasma torches, as well as the typical current and voltage oscillograms, are presented.

The results of numerical experiments on the modeling of the thermodynamic parameters of the shock-wave loading of silicon nitride Si₃N₄ and mixtures based on it are presented. A thermodynamically equilibrium model is used to account for the phase transition of Si₃N₄ during the shock-wave impact. The thermodynamic parameters of shock-wave loading are described for pure silicon nitride, as well as for mixtures of Si₃N₄ with potassium bromide KBr, periclase MgO, and aluminum nitride AlN. The computation results are compared with experimental data obtained by different authors.

The temperature dependence of the heat capacity, the heat transfer coefficient, and the change in the thermodynamic functions (enthalpy, entropy, and Gibbs energy) of AK12M2 alloy modified by calcium has been studied in the “cooling” mode. The heat capacity of alloys has been measured on a set-up based on the C-calorimeter method with a heat meter and an adiabatic shell. The results of the study showed that, in the temperature range of 300–550 K, the heat capacity increases by 20.1–21.4% for AK12M2 alloy modified with 0.1–1.0 wt % calcium. As the calcium content increases, the heat capacity of the initial alloy decreases by 4.86–6.41%.

The results of an experiment with pulse current heating of high purity iron are presented: temperature dependences of the specific energy input and specific heat up to 4000 K. The specific heat of the liquid iron is shown to be constant C_p ≈ 0.9 J/(g K) at both normal and high (up to 10 kbar) pressure.

In this paper, we studied the shock wave phenomena generated by laser pulses in a film sample of titanium diboride with a thickness of 1 μm by interferometry in the picosecond range. The splitting of the shock wave into elastic and plastic waves with a compression pressure of 43 GPa behind the front of the elastic precursor is recorded. The values of shear and bulk strength at a deformation rate of 8 × 10⁸ s^–1 are determined.

An experimental study on the explosive fragmentation of strongly heated lead melt inside a steel cup in distilled subcooled has been conducted. Analysis of high-speed video recordings of the process showed that an explosion can be initiated both with complete and partial hardening of the upper lead melt layer. The observed phenomena are described. The results may be useful for the determination of causes of the initiation of a steam explosion when the melt contacts with a solid surface or is partially crystallized.