Том 54, № 3 (2016)

The experimental investigation of turbulence in the nozzle behind grids and spheres as the instrumentation for turbulent combustion of premixed flows by means of PIV and thermoanemometry was carried out. These methods were compared and applied in turbulent flows behind grids and spheres. Flows with relatively low turbulence intensities of the mean flow velocity (~1%), corresponding to the laminar flow in the case of absence of obstacles at low flow rates were investigated. Numerical simulation of the flow in a channel with changing geometry was carried out. A good agreement between laboratory experiments and numerical simulations was obtained. The developed experimental device is recommended for use in turbulent combustion of premixed flows.

Investigation of explosive vaporization with pulse heating of an extended liquid in a pressure range of from–10 tо +0.1 МPа revealed regimes when bubbles occur by the homogeneous fluctuation nucleation mechanism. These regimes are distinguished by a great phase transformation rate and a nucleation concentration at the moment of the attainment of a certain liquid temperature. This metastable liquid temperature is found to be the highest and is estimated by coordinates of the liquid–vapor spinodal. The kinetics of cavitation and boiling is investigated by disturbance of the heat flux of a miniature, fast-heated wire sensor. The extended liquid pressure near the sensor was set by the method of the positive pressure pulse inversion. Experimental results are generalized with application of explosive vaporization theory for the impact boiling regime at positive pressures.

Roughness is one of the principal factors influencing reflectance of a surface that takes place in radiation heat transfer. In the present work, we investigate the influence of the orientation of single-oriented roughness grooves on the directed–directed spectral reflectance of surfaces within the wavelength range of 0.2–20.0 μm. The surfaces have a mean square deviation of the roughness (σ) of 0.2 μm and 2.0 μm and the areas exceed the size of the incident light beam. The angles of reflection are equal to the angles of incidence and are equal to 50° and 70°. The degree of influence of the groove orientation on the reflectance is defined as the ratio of the reflectances of one and the same surface with the grooves oriented parallel and perpendicular to the plane of incidence. In the theoretical investigation, we engage the unidimensionally rough surface model. An experimental study by means of physical modeling was performed: the degree of influence of the groove orientation on the spectral reflection of the surface was estimated, within the investigated wavelength range, according to the degree of influence of the groove orientation on the monochromatic reflectance of the reference ground surfaces within the σ-range of 0.01–4.33 μm on the wavelength 0.405 μm. The studies performed show that the spectral range of the groove orientation influence on the surface reflectance increases with an increase in σ and a decrease in the angle of incidence; the degree of that influence has a maximum the value of which increases with the increase in the angle of incidence. We determine the conditions of agreement of the theory and the experiment.

The experimental results of rewetting of overheated vertical copper heater with a low-thermal-conductive coating by a falling nitrogen film are presented. It is shown that the presence of the coating affects significantly the feature of the temperature curves and decreases the total plate cooling time by more than fourfold. The experimental data obtained earlier showed that the rewetting front propagating over the copper plate without coating was one-dimensional. It is revealed by comparison of the experimental data that the presence of the low-thermal-conductive coating results in the appearance of the front of a cellular structure with regular boiling jets, characteristic of rewetting of overheated thin plates. The synchronized measurements of the plate temperature and high-speed video recording of the transition processes show that the higher rate of cooling in the presence of the coating is associated with the development of intense boiling in the rewetting front at a much higher temperature of the plate.

An ionized flow around the RAM C-II space vehicle is studied by the direct simulation Monte Carlo method in the range of altitudes of 73 to 81 km. It is shown that the predicted value of the plasma density in the shock layer essentially depends on the approach to simulation of high-temperature nonequilibrium dissociation. Good agreement of the results of numerical simulation with flight experiment data is obtained.

The problems of increasing the cooling capacity of hydrocarbon fuel by its thermochemical transformation in elements of thermal protection of a hypersonic flight vehicle and hydrogen production on board for providing stable burning in a scramjet are considered. A comparison of the chemical reactions of cracking and steam conversion of hydrocarbons, as regards the cooling capacity and amount of hydrogen in reaction products, is made. The process of steam conversion of methane in a thermochemical reactor and the factors influencing the conversion level of hydrocarbons are studied experimentally.

Physical, mathematical and numerical models for the problem of the outflow of a jet of rarefied plasma from the nozzle of a plasma thruster of the cylindrical and rectangular shape have been considered. The main results of computation experiments have been presented: distribution functions of charged particles in the plasma flow, velocity and concentration fields of charged particles, and isolines of the potential of the self-consistent electric field.

Following the course of previously published series, this work studies in detail the correlation of the volumetric thermal expansion coefficient β(T) and the heat capacity C(T) of refractory tantalum. It is demonstrated that a clear correlation β(C) takes place in the lower temperature range and remains up to the metal melting point inclusively. Significant deviation from lower temperature linear behavior of the β(C) dependence occurs when the heat capacity reaches the classical 3R Dulong–Petit limit. The temperature dependence of differential Grüneisen parameter γ' ~ (∂β/∂С) is estimated.

The experimental works devoted to studying the generation and dynamics of concentrated air and fire vortices are reviewed. The main characteristics of stationary and nonstationary vortices, as well as free and confined air and fire vortices, are considered.

The free energy of simple liquid metal in the approximation of the integral smallness of the electron–ion interaction has been found on the basis of the model of single-component plasma as the initial system. The result obtained holds at the equivalency of correlation functions determined within Gibbs canonical and large canonical distributions.

The average and pulsating thermal characteristics at the stagnation point of a plate at inflow of an impact axisymmetric air jet have been studied. The influence of the Reynolds number (100 < Re < 12000) on heat transfer has been investigated for a jet flowing from a long tube (diameter d = 5 mm, relative length h/d = 200) with the output located at a distance h/d = 20 from the obstacle. The measurements have been carried out using a heat-flow sensor with high spatial and temporal resolutions. A nonmonotonic change in heat transfer having a maximum is found in the range Re < 4000 (in contrast to the known monotonic increase in heat transfer). A significant increase (200–600%) in the Nusselt number is observed for outflow from a tube in comparison with jet outflow from a nozzle. At Re > 4000, the difference in heat transfers for two cases of jet formation (from a tube and a nozzle) decreases asymptotically.

The effect of thermal training of a functional surface fabricated by means of femtosecond laser surface processing on a crystalline silicon (c-Si) surface is found for the first time. Hydrodynamic and thermal properties of the c-Si surface are revealed to be considerably modified by femtosecond laser processing and follow-up thermal training. The carried out experimental studies of wetting, evaporation, and boiling processes on the thermal trained laser processed surface open up ample opportunities in creation of tailored functional surfaces for micro/optoelectronic devices and power engineering applications.