Home – Home – Jornals – Thermophysics and Aeromechanics 2017 number 1

The equations of the longitudinal motion of flying vehicles at their steady and unsteady motion are considered. The nondimensionalization of equations has been carried out, and the similarity criteria have been obtained. The capabilities of the experimental modeling of the unsteady motion of flying vehicles are illustrated with the aid of small-scale models.

Nonequilibrium flows of a two-component oxygen mixture O₂/O behind a shock wave are studied with due allowance for the state-to-state vibrational and chemical kinetics. The system of gas-dynamic equations is supplemented with kinetic equations includ-ing contributions of VT (TV)-exchange and dissociation processes. A method of the numerical solution of this system with the use of the ANSYS Fluent commercial soft-ware package is proposed, which is used in a combination with the authors’ code that takes into account nonequilibrium kinetics. The computed results are compared with parameters obtained by solving the problem in the shock-fitting formulation. The vibrational temperature is compared with experimental data. The numerical tool pro-posed in the present paper is applied to study the flow around a cylinder.

The paper presents hyperbolic models for dusty gas flow formulated for single- and multivelocity approximations with account for inter-fractional heat transfer. Characte-ristic analysis of equations for the model was performed. The Godunov method and linearized Riemann solver was applied for a solution on curvilinear mesh: the Prandtl–Meyer problem for air-droplet mixture was solved. The simulation results were compared with the self-similar solution.

A numerical study of the aerodynamics of a building of a complex shape has been performed taking into account the location of surrounding buildings. Simulation data based on full mathematical models of continuum mechanics have allowed us to reveal the spatial structure of the turbulent separated atmospheric flow in the neigh-borhood of the building, and to evaluate the wind load exerted on the building. A comparison between the calculated data for the air flow past the examined building located in a group of other buildings and past the same building at its isolated location was performed. Based on the obtained data, the impact of interference effects on the aerodynamics of buildings in urban areas was evaluated. A comparison of calculated with experimental data was performed. A satisfactory agreement between the two datasets was obtained.

Dynamic characteristics of an ohmic heater intended for heating the working-gas flow in hot-shot wind tunnels have been experimentally studied. The experiments were per-formed on a specially designed test facility. Experimental data on the dynamic characteristics of the heater were obtained.

A mathematical model was developed for conjugate heat transfer in a heterogeneous system "solid body – gas-liquid medium" with account for vapor generation at the surface of hot metal cylinder with cooling by a longitudinal water flow. Results are presented for numerical parametric calculations for influence of thermophysical and hydrodynamic characteristics on the pattern of vapor generation at the cooled cylinder surface.

This paper presents experimental results of investigation of high-intensity cooling of high-temperature metal heater by subcooled ethanol flow. The experiments have proved the presence of self-excited pressure pulsations with amplitude of 1.15 MPa, arising in ethanol. Expanding real signals of the sensors by the Hilbert–Huang trans-form has resulted in the intrinsic mode functions. Analysis of these functions and the high-speed video shooting results allows identifying the basic frequencies and me-chanisms of pressure oscillations. Comparison of the results with the data of film cooling and bubble boiling on the cooled heater has shown that maximum values of non-stationary heat-transfer coefficients for the self-excited oscillations and for the bubble boiling are the same.

Dynamics of a cavitation bubble is considered at its strong expansion and sub-sequent compression. The bubble is formed by merging of two identical spherical cavitation microcavities in the pressure antinode of the intensive ultrasonic standing wave in the half-wave phase with negative pressure. Deformations of bubble and deformations of radially converging shock waves occurring therein at bubble compression are studied depending on the size of microcavities forming the bubble. It is found that compression of the medium in the bubble by the converging shock wave is kept close to the spherical one only in the case, when the radius of merging microcavities is 1800 times smaller than the radius of the bubble formed by merging at the time of its maximal expansion.

The paper presents the experimental results for velocity and tempertaure disibutions of the condensed phase in a plasma jet from the plasmatorch PNK-50 (design from ITAM SB RAS, Novosibirsk). The plasma jet is used at different operational modes for thermal spraying of nickel alloy powder PR-NKh16SR3. The measurements for aver-age velocity (230–280 m/s) and temperature (2290–2410 K) of sprayed particles were matched to data on microhard-ness (630–710 HV) and porosity (1.7–13.5 %) of samples. Results were transferred into coating properties maps plot-ted in coordinates "arc current vs. torch offset" and "particle velocity vs. particle temperature". Experiments demons-trated the change in parameters of condensed phase in the jet after performimg of maintenance job for the plasma-torch. We propose the method for adjusting the operational parameters of thermal spraying equipment using optical methods of control for particle velocity and particle temperature. The exemplary apparatus function of the plasmatorch was plotted; an approach is proposed for optimization and transfer of spraying technology of coatings with specified properties between equipment from different manufacturers, different class and power.

The present study investigated fluid flow and natural convection heat transfer in an enclosure embedded with isothermal cylinder. The purpose was to simulate the three-dimensional natural convection by thermal lattice Boltzmann method based on the D3Q19 model. The effects of suspended nanoparticles on the fluid flow and heat transfer analysis have been investigated for different parameters such as particle vo-lume fraction, particle diameters, and geometry aspect ratio. It is seen that flow beha-viors and the average rate of heat transfer in terms of the Nusselt number (Nu) are ef-fectively changed with different controlling parameters such as particle volume fraction (5 % ≤ φ ≤ 10 %), particle diameter (d_p = 10 nm to 30 nm) and aspect ratio (0.5 ≤ AR ≤ 2) with fixed Rayleigh number, Ra = 105. The present results give a good approximation for choosing an effective parameter to design a thermal system.

The paper deals with justification of the formula for the latent heat of phase transition of the first kind, taking into account superheating and subcooling of the formed two-phase system, in application to the solution of Stefan problem in semitransparent ma-terials.

The influence of mixed convection boundary layer flow of a viscoelastic fluid over an isothermal horizontal circular cylinder has been analyzed. The boundary layer equa-tions governing the problem are reduced to dimensionless nonlinear partial differential equations and then solved numerically using Keller-box method. Skin friction coeffi-cient and Nusselt number are emphasized specifically. These quantities are displayed against curvature parameter. Effects of mixed convection parameter and radiation-conduction parameter on skin friction coefficient and Nusselt number are illustrated through graphs and table. The boundary layer separation points along the surface of cylinder are also calculated with/without radiation, and a comparison is shown. The presence of radiation helps to reduce the skin friction coefficient in opposing flow case and enhances it for assisting flow case. The increase in value of radiation-conduction parameter helps increase the value of skin friction coefficient and Nusselt number for viscoelastic fluids. The boundary layer separation delays due to thermal radiation.

Thermal conductivity of R–410A mixture in the vapor phase (314–428 К and 0.1–2.0 MPa) has been studied by the steady-state method of coaxial cylinders. Experimental uncertainties of temperature, pressure, and thermal conductivity measurements did not exceed 0.05 K, 4 kPa, and 1.5–2.5 %, respectively. The approximating equation has been obtained for thermal conductivity depending on temperature and pressure. Thermal conductivity on dew line and in ideal-gas state has been calculated.

Results of experimental studies of electrode erosion in high-current arc discharges are presented. Available data on the service life of electrodes in the arc plasma generators sometimes are contradictory and do not give the whole pattern on the relationship of specific erosion of the electrode material with the basic determining parameters of the plasmatorch. The real ways to increase the duration of plasmatorch operation before electrode replacement have been proposed.

The results of mathematical modeling of the thermal state of combustion chambers with regenerative cooling for ramjet engines of promising flying vehicles are presented. The cooling of combustion chambers by the gasification products of a combined charge of the energy-intensive material is considered, where the polyethylene is used as a stuff, and the HMX-based compounds are used as the active substance. The flow rates of the cooling eneregy-intensive material are determined, which provide acceptable levels of temperatures of combustion chambers at various modes of engines operation are determined.

The article considers some aspects of the research methodology of micro heat power plants based on internal combustion engines with air cooling and cogeneration based on energy balance equations and the laws of heat transfer. The research is conducted for such a setup based on the Hitachi internal combustion engine with 2.4 kW capacity. It has shown the efficiency of cogeneration use in the form of useful heat flow from air, cooling the cylinder head, with its further heating by utilizing the heat of flue gases in an additional plate heat exchanger. It has been shown that the cogenera-tion can save fuel costs 3–10 times compared with heat guns, depending on the duration of the setup use.