Home – Home – Jornals – Thermophysics and Aeromechanics 2013 number 5

In the present paper, we consider instrumentation and the experimental procedure for conducting tests in a high-enthalpy short-duration wind-tunnel facility, namely, a hypersonic hot-shot wind tunnel. We consider operation of the hot-shot wind tunnel with the test gas (TG) parameters kept constant during the regime and also operation of the tun-nel as a traditional shock tube with a decay of the TG parameters that occurs as the TG leaves a constant-volume settling chamber. Stabilization of the TG parameters is achieved by using a pressure multiplier installed coaxially with the settling chamber, the configuration presenting a linear arrangement of the two components. Unloading of pressure multiplier dynamic component is achieved by using an equalizer whose piston moves in the opposite direction to the multiplier piston system. Several modes of wind tunnel operation with various combinations of different TG heating methods (electric arc, chemical energy, adiabatic compression, or heating in an external with respect to the settling chamber heat source) are possible. The design of a device responsible for diaphragm breakdown delay is considered. The design and dimensions of the wind tunnel provide for its normal operation under the following conditions: range of Mach numbers М = 4-20, range of settling-chamber temperatures Т_ch1 = 600-4000 K, and settling-chamber pressure р_ch1 up to 200 MPa (in operation with a double settling chamber, the stagnation pressure р_0n = р_ch2 can be varied from 1 to 200 MPa). The settling chamber volume (80-100 dm³) is sufficiently large, allowing obtaining a 1-m diameter hypersonic stream in the test section during ~ 100 ms (in combination with a second settling chamber).

The exergy method is developed for computing the ramjet thrust-economic characteristics with regard for real thermodynamic properties of combustion products when using as fuel the hydrogen and hydrocarbon fuel for the freestream Mach numbers M = 4 ÷ 14. The estimates for the specific impulse of the given engine using the presented technique are shown to agree with the estimates computed by other authors. The computational method is intended for obtaining the ramjet characteristics and conduction of the parameter analysis at the research initial stage as well as for its use at the conceptual developments of hypersonic flying vehicles.

A novel approach to modeling high-temperature nonequilibrium dissociation in air at a level of molecular collisions is proposed. Information on the energy dependence of the specific reaction cross sections, which is necessary for such modeling, is determined numerically from available macroscopic information on the dependence of the reaction rate constant on translational and vibrational temperatures. The results of Direct Simulation Monte Carlo (DSMC) computations show that the proposed model yields a correct reaction rate in vibrational-translational nonequilibrium. The use of the new model in DSMC computations of high-altitude aerothermodynamics results in obtaining a noticeably different flow structure and a higher heat flux, as compared to that predicted by standard DSMC models (such as the total collision energy model).

A physical and mathematical model is developed for heat and mass exchange processes at the absorption of gaseous components from vapor-gas mixtures in bubblers. The intensity of these processes in the foam and centrifugal bubblers depends overall on the conditions of their passing in single bubbles forming on the orifices of gas distribution grates. The constructed model, as was shown by its numerical realization for specific conditions, is confirmed by known experimental data and can be used for engineering computations of thermal and mass exchange parameters of bubblers and the optimization of their operation regimes.

A method for calculation of unsteady 3D turbulent flows in hydro turbines of power plants developed for simulation of the transient processes is presented herein. The method is based on joint solution to the Reynolds-averaged Navier—Stokes equations for incompressible fluid flow written for moving mesh, the equation of runner rotation and the system of 1D equations describing propagation of elastic hydraulic shock in the flow domain. The exchange in flow parameters between the penstock and hydro turbine regions is considered in this approach. Results of transient processes simulation are presented for several modes: start-up to the turbine regime, instantaneous load shedding, and output power decrease. Comparison with experimental data is performed.

The paper presents an experiment on superheated n-pentane boiling-up in a glass capillary at atmospheric pressure using a high-speed video. The video shooting was first performed in two mutually perpendicular directions. Two obtained images allowed concluding, on which side of the vessel wall the bubble forms, and whether we observe one bubble with an image, deformed due to the curvature of the capillary, or two bubbles located nearby. These data prove the surface (heterogeneous) character of boiling-up.

The article presents additional calculated data on combustion velocity for typical gas mixtures at pressures up to 6000 atm and temperatures up to 4000 K. It was determined that combustion velocity is mainly influenced by initial temperature, and the dependence on pressure is rather low. For fuel-oxygen and air-fuel mixtures in three-dimensional space (pressuretemperaturevelocity of deflagration combustion), we have found a single surface of combustion velocities and continuous dependence of flame velocity on initial conditions.

In the present work, conjugate heat transfer in a rectangular cavity with a heated moving lid is investigated using the lattice Boltzmann method (LBM). The simulations are performed for incompressible flow, with Reynolds numbers ranging from 100 to 500, thermal diffusivity ratios ranging from 1 to 100, and Prandtl numbers ranging from 0.7 to 7. A uniform heat flux through the top of the lid is assumed. Results show that LBM is suitable for the study of heat transfer in conjugate problems. Effects of the Reynolds number, the Prandtl number and the thermal diffusivity ratio on hydrodynamic and thermal characteristics are investigated and discussed. The streamlines and temperature distribution in flow field, dimensionless temperature and Nusselt number along the hot wall are illustrated. The results indicate that increase of thermal diffusivity yields the removal of a higher quantity of energy from lid and its temperature decreases when increasing the Reynolds and the Prandtl numbers.

An absolutely new setup for production of high-temperature silicate melts with application of energy of low-temperature plasma is considered in this paper. The mathematical model “stream function  vorticity” was developed and numerically implemented in transformed variables. This model describes the unsteady regimes of convective heat transfer in the melting furnace. The effect of time and electric current density on the flow structure and heat transfer was studied. The features of hydrodynamics caused both by unsteady character of the process and significant dependence of thermal-physical characteristics on temperature were identified.

The approach based on relative emissivity was tested and developed using the experimental data. It was assumed that the medium separating an opaque body and measuring device was diathermic or nonradiating (it is characterized by its transmittance); radiation source emissivity and medium transmittance were unknown. Data on comparison of spectral radiances (spectral intensities), obtained within 220–2500 nm for the temperature lamps in the metrological laboratories of Europe, Russia, and USA were used as the initial experimental data. It is shown that the use of relative emissivity allows graphical interpretation for the solution to the initial nonlinear system of equations. In this case, the problem of determining the true temperature of the body by the thermal radiation spectrum in a graphical interpretation is reduced to the choice depending on relative emissivity at the desired temperature. It is shown that to narrow the interval, which includes the true temperature, the criterion was based on a change in convexity of spectral dependence of the relative emissivity in the process of desired temperature selection. The use of relative emissivity in a spectral range, where the Rayleigh—Jeans approximation is satisfied, allows unambiguous determination for the shape of emissivity dependence on the wavelength. The relationship for determination of the peak wavelength within the registered thermal radiation spectrum on the basis of data about the true temperature of the body and its spectral emissivity is presented.

It was found that bulk samples of molybdenum are oxidized by supercritical water forming nanoparticles of monocline MoO₂. The average size of nanoparticles obtained at uniform heating of with supercritical water was about 27 nm, and the size of agglomerates of nanoparticles was ≤ 1 μm. From time dependence of the amount of formed H₂ n_H2 (t), we have determined kinetic parameters of transition to MoO₂ particles. The dependence dn_H2 / dt is characterized by the presence of two pronounced maxima. This is explained by the change of mutual diffusion of H₂ and H₂O molecules along with the growth of thickness of the layer of MoO₂ nanoparticles.

Laser flash method with 2–4% accuracy was used to determine the coefficient of thermal diffusivity of ferrite-martensite steel ChS-139 in temperature range 296–1274 K. Temperatures of Curie and martensite-austenite-martensite phase changes have been determined.