Vol 57, No 3 (2019)

The current research is focused on the study of methane-air flame stabilization under the flow geometry variation for normal and upside-down (reverse) flame orientation. The experimental studies of plane-symmetrical rod-stabilized flames under the normal and reverse-oriented gravity conditions were carried out. The results of numerical simulation are presented. The blow-off is shown to be the function of stabilization-body position. We consider both V-shaped and M-shaped plane-symmetrical open flames for different Reynolds numbers, fuel-air ratio and flame orientation relative to the gravity direction. Blow-off limits appear to be independent on the gravity for the lean methane-air mixtures while the quenching processes are different for the normal and reverse-oriented gravity conditions. Blow-off is also accompanied by the chemiluminescence intensity decrease under reverse-oriented gravity conditions, which is exhibited in localized plume extinction and gradual quenching. While under the normal gravity, it appears via stepwise vortex separation from the lateral plume parts. Under such conditions chemiluminescence intensity remains almost constant. The blow-off time scale under the normal gravity conditions is bigger as compared to reversed-oriented ones by several times.

The article presents an analysis of the results of an experimental study of the dynamic and thermal characteristics of the turbulent boundary layer of the air near a heated plate at q_w = const with rectangular ribs having slit channels of different geometry: confusor, diffuser, and plane-parallel. The slit channel is located between the plate and the lower rib wall. The results are compared with similar data for a solid rib without the slit channel. A Pitot–Prandtl microprobe with a microthermocouple and the Dantec Dynamics hot-wire anemometer were used, thus making it possible to study the laminar sublayer, the transition domain, and the outer part of the boundary layer. The influence of the slit profile on the average and the pulsation characteristics of the turbulent dynamic and thermal boundary layers in the median section of the plate with the slit rib is revealed. It is found that the separated zone disappears in the flow behind the ribs with the confusor slit.

The results of experimental research on the horizontal discharge of heated gas and overheated water through nozzles with channels having a round cross-section and different cutoff angles of the outlet aperture are presented. The processes of liquids and gases discharge are visualized via photographic survey and thermal-imaging diagnostics. Comparative analysis of the main characteristics of liquid and gas jets discharged at different initial conditions and channels of different configurations is performed. It is established that there is no shift in the jet axis with respect to the outlet-aperture axis during the discharge of heated gas through nozzles with a cutoff. Different behavior is observed during the discharge of overheated water through nozzles with a cutoff. In this case the jet axis is shifted towards the cutoff direction with respect to the outlet-aperture axis, which is in the interval 15°–18° depending on the initial conditions. Practical recommendations on the use of the discovered mechanisms in engine technology (during fuel atomization by nozzles) are suggested based on the research results.

The Graetz–Nusselt problem for Bingham liquid is solved by the approximate Kantorovich method. The solution is obtained in the form of a Fourier–Bessel series. The internal heat release at the expense of viscous dissipation is taken into account. Expressions for the temperature and local Nusselt number are obtained. The results of numeric analysis of the solution are presented.

The dynamics of detonation waves in chemically active bubbly liquid is considered based on numeric simulation with consideration of the relative motion of phases. The influence of the parameters of the initial state of the medium (pressure and volume gas content) on the structure and propagation velocity of detonation waves is studied. Comparative analysis with known experimental data is performed.

A kinetic theory of high-voltage glow discharge is developed with allowance for secondary electron emission and thermal emission. Poisson’s equation is solved for the space charge layer with allowance for the ion flux from the plasma to the layer and gas ionization in the layer by electrons, ions, and fast atoms. There are potential and kinetic ejections of electrons from the cathode surface. The current–voltage characteristics are calculated, the sizes of the space-charge layer are determined, and the electric-field distributions in the layer and some other characteristics of discharge with combined emissions are obtained for different ratios of the thermal emission current density to the secondary electron emission current density. It is shown that the thermal emission significantly affects the discharge parameters.

Methods are proposed for the spectral measurement of electron temperature Т_е in a highly ionized nonequilibrium He plasma at atmospheric pressure based on a comparison of the intensities of atomic and ionic lines with a whole complex of experimental data (primarily, n_e). The large energy gap between the emitting HeI and HeII excited levels (of more than 50 eV) and allowance for the nonequilibrium manifested in the overpopulation of the atomic levels with respect to the ionic levels make it possible to make reliable and simple Т_е estimates, especially if the ionization energies of the emitting levels of the atom and the ion are close. For practical use, three pairs of HeI and HeII lines observed in the spectral range of 200–1100 nm are recommended. The radial and temporal (upon the quasistationary pulsed heating of the electric arc plasma) dependences of Т_е are obtained in the range of axial values of 3.2–4.7 eV.

The influence of the longitudinal distribution of heat release in a supersonic combustion of propane under the conditions of an unsteady pulsed discharge on the gas flow regime in a rectangular channel with a variable cross section is studiecd. It is shown that, with an increase in the mass flow rate of propane, the thrust arising from the supersonic combustion of a lean hydrocarbon fuel in an expanding aerodynamic channel, the pressure jump in the combustion area, and the air temperature in the closed pressure chamber increase. It is revealed that there is a limiting amount of hydrocarbon fuel that can be burned in a supersonic combustion regime in an expanding rectangular aerodynamic channel with side expansion angles α = β = 5° without transition to a subsonic flow, while the ratio of the exit and entry sections S₂/S₁ is 12.7. The experimental results are in satisfactory agreement with the data of mathematical modeling with allowance for additional heating of the cold supersonic flow in the region of an unsteady pulsed discharge.

A heterogeneous recombination of nitrogen and oxygen atoms is considered. The installation and the method to determine the probability of heterogeneous recombination of oxygen and nitrogen atoms by resonance fluorescence spectroscopy under strictly controlled conditions are described. The variation of the recombination probability of nitrogen and oxygen atoms on the quartz surface is studied in the temperature range of 297–1000 K and pressures of 0.01–10 mbar. The regions of pressure and temperature in which recombination occurs predominantly according to the Langmuir–Hinshelwood mechanism or the Eley–Rideal mechanism are distinguished. Data on the recombination activation energy are presented. The recombination of nitrogen and oxygen atoms occurs mainly at various active centers.

In this paper, we experimentally studied the adiabatic compressibility β of an exfoliating liquid mixture, LiF +KBr, on the saturation line in a temperature range from the melting point to the critical mixing temperature using the sound velocity u measured by the pulse method and the density ρ determined by hydrostatic weighing based on the ratio β = u^–2ρ^–1.The coefficients of the temperature dependences of the compressibility and density of the upper and lower equilibrium phases are shown to have opposite signs due to the superposition of the thermal motion of ions and changes in the phase composition. The reduced differences β* and ρ* ​​for the contacting phases decrease with decreasing reduced temperature T* in accordance with the empirical exponential equations β* ≈ T*^1.017 and ρ* ≈ T* ^0.494.

A system of equations is developed to calculate the properties of dissociated steam in the temperature and pressure ranges of 1250–3400 K and 0.01–10.00 MPa. These equations are based on detailed tables for dissociated steam compiled for a mixture of atoms of hydrogen and oxygen, hydroxyl OH, molecules of hydrogen and oxygen, and steam at a reference temperature of 0 K. Since the expansion of dissociated steam in a thermal engine results in its transformation into its common form, the equations for the parameters of dissociated or nondissociated steam uses the same reference temperature, i.e., the water triple point of  273.16 K. A system of equations for the calculation of dissociated-steam properties is derived with the generalized thermodynamic equation, which takes into account the change in the chemical potential and the composition of the mixture during steam dissociation, the Gibbs energy equation, differential thermodynamic equations, and equations for calculation the properties of nondissociated steam. To minimize the deviation of the steam properties calculated by the proposed equations from the table values, the considered temperature and pressure ranges have been divided into three regions. The deviation of the steam properties calculated by the proposed equations from the table values does not exceed 0.05–0.09%. The developed equations can be used in calculations of the processes of cooling of burners and combustion chambers during the combustion of hydrogen–oxygen mixtures, as well as cycles of heat engines that use high-temperature steam as a working fluid at temperatures over 1250 K.

The work presents the results of an experimental study on the core speed of ultrasound, the relative thermal expansion, the densities, and the Young’s modulus calculated based on these data for several hardened and annealed steels in a wide temperature range. The experimental data were processed by the least-squares method, which made it possible to obtain approximating equations for the temperature dependences of the studied and calculated properties of steels.

A brief critical analysis of the theoretical P(T) liquid–vapor phase equilibrium curves is given. Based on the Clapeyron–Clausius equation and data on the heat capacity of water, a two-parameter expression of the P(T) curve is obtained for water in the temperature range from the triple point to 389 K. The parameters of the P(T) curve are determined from data on the pressure and heat of evaporation of water at the triple point. The accuracy of the P(T) function is comparable to the actual accuracy of standard thermodynamic tables for water and water vapor.

The propagation of acoustic waves in multifraction gas suspensions with polydisperse inclusions has been studied. The disperse phase contains N fractions, which differ in size, the size-distribution functions of inclusions, and materials. The dispersion relation, which determines the dependence of the complex wavenumber on the perturbation frequency, is obtained. The dependences of the relative speed of sound and attenuation coefficient on the dimensionless perturbation frequency are obtained. The effect of heat transfer is analyzed.