Vol 56, No 2 (2018)

A theoretical method for the determination of an electric field near a paraboloidal metal (conducting) tip has been proposed. The accuracy of the proposed numerical solution has been analyzed. The dependence of the electric field strength at the tip vertex on the distance to the plane, which is applicable for predicting fields in various physical problems and engineering calculations, has been considered. The characteristic spatial distributions of the electric potential and field are presented.

It is shown based on explicit expressions for structural factors and longitudinal and transverse permittivities of degenerate electron plasma within the ideal-gas approximation that temperature effects should be taken into account in these functions to correctly describe the region of small values of wave vectors and frequencies.

This work presents the detailed joint study of temperature dependences of thermal expansion and heat capacity of solid beryllium. It is shown that, as for the earlier studied solid bodies, within the limits of experimental and statistical errors, the heat capacity C(T) and the temperature coefficient of volume expansion β(T) in the entire range of the HCP-phase of metal are in a pronounced correlation β(C) that has a typical (as earlier) “bilinear” form consisting of two smoothly conjugate linear sections with the up-fracture hitting the classical Dulong and Petit heat capacity limit 3R. The consistent values of the heat capacity obtained and the thermal expansion are tabulated and an estimate of the temperature dependence of the Grüneisen differential parameter γ′ ~ (∂β/∂C) is given.

The thermodynamic temperature of an opaque material with unknown emissivity was determined from the recorded distribution of spectral intensities of the emitted radiation. The initial system of equations was derived in the logarithmic form in accordance with the Planck formula. At the first stage, the spectral dependence of the material emissivity was investigated with a special function—relative emissivity. Based on the analysis of spectral dependences of this function at different reference temperatures, a parametric model for the material emissivity was chosen. At the second stage, the desired parameters of the chosen model of spectral emissivity and the thermodynamic temperature of the material were determined. An example of the determination of a temperature of a tungsten sample from the spectral distribution of emitted radiation intensities is given. A method for narrowing the range, which includes the thermodynamic temperature of the material, is presented.

Some experimental data on the heat transfer in different meshed metallic materials with interchannel heat-transfer fluid transpiration and two-dimensional intermesh flow are presented. It is established that the thermal conductivity of a wire mesh material and the relative pathway, intermesh velocity, and thermophysical properties of a heat-transfer fluid has an effect on the heat transfer in meshed metallic materials with the two-dimensional flow of a single-phase heat-transfer fluid.

The variational form of a mathematical model of a thermal explosion has been developed based on a variational formulation of a nonlinear problem of stationary thermal conductivity in a homogeneous solid body. The model takes the temperature dependence of the thermal conductivity of a solid body into account. The presented example of quantitative analysis of the model demonstrates a method for finding the combination of parameters for determining a thermal explosion in a plate with an exponential temperature dependence of the thermal conductivity. At the same time, the analysis allows one to identify the number of steadystate temperature distributions inside a body whose energy release intensifies with a temperature increase.

The results of numerical modeling of the microwave heating of a water-in-oil emulsion drop in a gravity field with consideration of the empirical temperature dependence of the viscosity of the liquid surrounding the drop are presented. The system of thermal convection equations is considered in the Boussinesq approximation. The solution is obtained by the control volume method with the SIMPLE algorithm and by the VOF method. It is established that the emerging convective structures result in nonuniform heating of the drop predominantly near the surface, which can lead to a local rupture of the armor envelope and the formation of fine-dispersed phase. It is shown that there is an optimal range of power of microwave field in which an intensive deposition of water drops occurs, which leads to water-oil emulsion breakdown.

The influence of the coflow wind on the flow in a hot, nonisobaric, supersonic airdrome jet from a biconical nozzle and its interaction with a jet blast deflector (JBD) are studied by the RANS/ILES method. The conditions at the external boundary of the computational domain are formulated for the problem of jet interaction with the JBD. All calculations were performed at the Joint Supercomputer Center of the Russian Academy of Sciences with a MVS-10P supercomputer. The features of method parallelization for the supercomputer with modern architecture are described. The total temperature of the jet at the nozzle output is T₀ = 1050 K and π_с = 4. The wind velocity ranges from 0 to 20 m/s. Two JBD positions are examined: at distances of 5 and 15D_e of the nozzle cross section. The computation grids consist of (6.33–8.53) × 10⁶ cells. Fields of the flow parameters and of their turbulent pulsations near the jet are obtained. The dimensions of the “safety zone” for people and machinery is determined by the temperature, pressure pulsations, and velocity near the airdrome surface. The influence of wind velocity on the size and shape of the safety zone are revealed. The distributions of pressure and temperature and their pulsations over JBD altitude are presented as a function of JBD position and wind velocity.

The working process in the regenerative gas generators of liquid rocket engines is analyzed and a method for computer simulation based on the Zel’dovich’s model of “quenching” the composition of the products of high-temperature combustion as a result of rapid cooling on supplying an excess of the low-temperature component and the resulting chemical quasi-nonequilibrium is developed. The method is implemented and tested on the basis of the TERRA software package in calculations of the composition and properties of the propellant produced by regenerative gas generators using oxygen as the oxidizer and methane as the fuel. The vacuum specific impulse of the considered fuel is calculated for the possible conditions of a quasi-nonequilibrium working process.

The paper presents a review of theoretical and experimental works devoted to two-phase (gas-solid) flows past bodies. The particularities of particle motion in the vicinity of bodies of various shapes and the influence of the disperse phase on the drag force and heat transfer are considered. Some consequences of the interaction of particles with body surfaces (erosive destruction, gasdynamic spraying, icing, and glowing) are analyzed.

We present experimental results on the behavior of the burning of electrical discharge between a nonuniform jet anode and liquid cathode and of the discharge voltage and current pulsations for various voltages of the power supply. We determine the frequency spectrum of the discharge voltage oscillations, as well as the temperatures on the electrolyte cathode surface, by means of infrared thermography and pyrometer.

The results of an experimental study of heat transfer in a water flow in a channel with a twisted tape insert with discrete ribs installed at an angle to the tape axis are presented. The experiments were performed in a straight smooth tube with an inner diameter of 10 mm. The tape inserts had a twist ratio of 2.5, 3, or 4 with a 180° rotation; the rib height ranged from 0.5 to 1.5 mm, the rib pitch was from 40 to 120 mm, and the rib angle was from 40 to 50° to the tape axis. The results of experiments in the mentioned range of geometries suggest that the ribbed tape inserts increase heat transfer by a maximum of 40% as compared with that in tubes with a twisted tape without ribs. The generalized correlation is given for the prediction of heat transfer in a Reynolds number range Re = 10⁴‒2 × 10⁵.

The objective of the present simulation is to analyze the performance of a twin thermoacoustic prime mover using CFD in terms of frequency and pressure amplitude. Pure fluid media such as helium, argon, nitrogen and their binary gas mixtures are studied at a constant operating pressure of 5 bar. The GAMBIT 2.3.16 pre-processor is used for creating the geometry of twin prime mover and the CFD package FLUENT 6.3 is used for simulating the device with different combinations of gas mixtures. The geometrical parameters and temperature gradients across the stack are kept constant throughout the simulation. It is found that the pressure amplitude of the thermoacoustic oscillations is higher for pure argon, whereas the frequency of the oscillations is higher for helium (495 Hz) rather than other gases and mixtures.