Thermophysics and Aeromechanics最新文献

The presented paper considers a number of problems, with the first of them concerning the analysis of experimental (ρ_l, ρ_g, T)-data of SF₆ at relative temperatures (1.5·10⁻⁸ < τ < 0.3). The second task is to develop combined models (ρ_l (D, C, τ), ρ_g (D, C, τ), …) that agree with a number of boundary conditions, including the requirements of the scale theory of critical phenomena. The third task deals with the calculation of (D, C)-parameters included in the combined models; at this stage, a basic array of (ρ_l, ρ_g, T)-data is formed. It contains: a) experimental results obtained in the laboratory of Prof. Funke (Germany) and b) (ρ_l, ρ_g, T)-data obtained by recalculating some values in the laboratory of Prof. Garrabos (France). The models ρ_l (D, C, τ) and ρ_g (D, C, τ) serve as the basis for computing some thermodynamic functions of SF₆ in the critical region; among them there are complexes, which consist of several properties (the average diameter of a binodal, the order parameter etc.).

One of the promising methods of geophysical research in operating wells is active thermometry. The method consists in creating an artificial temperature field in a well due to local heating of the metal casing. Observation of heat tags movement enables determining the fluid flow rate in the well and identifying the intervals of the behind casing flow.

The article is devoted to the study of non-stationary thermal processes in a well during induction heating. The calculations were performed in the commercial simulator Ansys Fluent. It was established that with an increase in the volumetric flow rate through the column from 5 to 50 m³/day for the modeling conditions, the maximum heating of the liquid (a change in the average mass cross-section temperature) is reduced by 85 %, and the maximum heating of the column is reduced by 7 %. The influence of natural convection on the formation of a temperature field in a liquid and a column has been studied. For the model with natural convection accounted, the column heats up significantly less than for the model without convection: the error in calculating the temperature changes due to neglect of natural convection can reach several hundred percent. During the process of induction heating for the casing, the effect of natural convection remains significant throughout the entire flow range of 5–50 m³/day.

Within the framework of linear subsonic theory, the problem of determining the effect due to wall interference on the flow around airfoil according to the pressure distributions measured on the airfoil and on the wind-tunnel test section walls is solved. For the test case (testing a BGK1 airfoil in the IAR1.5m wind tunnel), we compared the wall interference corrections to freestream Mach number and airfoil angle-of-attack that were obtained using our method and in the works by other authors. For an OSPB-77 airfoil model tested in the T-128 wind tunnel for two values of wall permeability, f = 0 and 3 %, corrections to distributed data and integral loads were applied in the range of Mach numbers from 0.2 to 0.78. The application of those corrections has made it possible to bring the results for f = 0 and f = 3 % in closer agreement up to the angles of attack at which flow separation occurs on the airfoil.

Modeling of processes with phase transition in confined spaces needs high-accuracy simulations with account for non-equilibrium. In the present paper, we use the direct simulation Monte Carlo method for describing evaporation into a vapor-filled half-space with a subsonic monoatomic gas flow. Two types of boundary conditions for open halfspace are considered: the iteration approach with consecutive calculation of temperature and pressure, and the approach with a fixed velocity. We compared these approaches for obtaining the accurate solution of the problem. The fixed-velocity approach provides a higher accuracy for the flow with a low Mach number. The calculated results are compared with a known solution of a model kinetic equation.

The paper presents the results of simulation and experiment for motion of a supersonic two-phase jet passing through a round aperture in a mask. The mask is placed at different distances from the substrate under the conditions of the cold spraying. The calculations were performed using the fluid dynamics software ANSYS Fluent; flow visualization is achieved using the Schlieren method. Solution analysis and comparison of results were performed for example of aluminum powder spraying.

The enthalpy and heat capacity of solid and liquid Mg₂Ca intermetallic alloy were measured by massive high-temperature isothermal drop calorimeter over the temperature range of 298.15–1177 K. The estimated errors in the data on enthalpy and heat capacity were 0.2 % and 2 %, respectively. The fusion enthalpy of the Mg₂Ca intermetallic alloy was determined to be 483 ± 3 J/g. The heat capacity of the Mg₂Ca melt was shown to be constant in the range of 993.2–1177 K. A comparison of the obtained results with literature data has been carried out.

Using the method of differential scanning calorimetry, the heat capacity of Mg-Ca alloys containing 10.50, 33.34, and 73.00 at. % Ca, being promising for various practical applications (biocompatible and biodegradable alloys, ultralight construction materials, anode materials, hydrogen absorbent materials, etc.) has been studied experimentally. New reliable experimental results on the heat capacity in the temperature range of 190–576÷692 K of the solid state have been obtained. The estimated errors of the received data were 2–3 %. The reference table for temperature dependences of heat capacity of Mg-Ca alloys has been compiled. It has been established, that over a wide temperature range the heat capacity of solid magnesium-calcium alloys can be estimated with high accuracy using the Neumann–Kopp rule.

Three-dimensional numerical simulation of a transverse hydrogen jet blowing into a duct with a supersonic flow of air (warmed by a fire heater) has been carried out. The study is based on experimental data obtained at the ONERA-LAERTE facility. The RANS equations for the reacting gas were solved, closed by the SST model and various kinetic mechanisms of hydrogen combustion in air. The channel wall roughness was taken into account in this model. The dependence of the flow characteristics on such physical factors as the shape of the fuel injector channel, the effective roughness height, and various methods of describing molecular diffusion has been studied. It has been established that the equivalent diameter of a grain of sand has a significant influence on the longitudinal pressure distribution in the duct. The influence of chemical kinetics on the flow structure in separation zones within the duct is demonstrated.

Phenol oxidation in a water-oxygen fluid in a tubular batch reactor with its uniform heating (1 °C/min) to 600 °C was studied. An increase in the amount of O₂ above the stoichiometric ratio by 25 % leads to an increase in the degree of carbon burnout by the factor of 1.09. Replacing 10 % of the stoichiometric amount of oxygen with nitrous oxide leads to the same increase in the degree of carbon burnout, primarily due to its afterburning at a temperature of ≥ 400 °C. Replacement of some part of phenol with isopropanol leads to an increase in the degree of carbon burnout by the factor of 1.02. It was established for the first time that the heterogeneous mechanism of phenol oxidation in a water-oxygen fluid is the main one. However, the overstoichiometric amount of O₂, as well as the addition of N₂O and isopropanol intensifies gas-phase combustion of carbon. A catalytic effect of a Pt-Rh/Pt-thermocouple on the degree of phenol conversion in the presence of O₂ at temperatures above 135 °C was found.

The present numerical study is aimed at revealing the influence of the nozzle exit-to-resonator edge distance on the gas-dynamic characteristics of the acoustic-convective flow in the flow path of a bichannel system. The aim of the work is the development of a computational technology for describing physical processes in the duct of multichannel systems that generate high-intensity acoustic fields. Five configurations of the bichannel system in which the gap between the nozzle exit and the resonator edge was 0.85, 1.10, 1.35, 1.60, and 1.85 of the resonator diameter, were analyzed. As a result of the study, a complete picture of the gas-dynamic flow formed in the duct of the bichannel system was obtained, including the resonating cavity and the region in between the nozzle and resonator. With the help of numerical simulation, the formation of a flow with high-frequency, low-amplitude oscillations at a small gap between the nozzle exit and the resonator edge, which was observed in experiments, has been demonstrated. Pure-tone oscillations with maximum intensity occur when the resonator is placed in the region of the beginning of the second barrel, this observation being in good agreement with the data obtained by other authors. Subsequent increase in the nozzle-to-resonator distance leads to the emergence of subharmonics and multiple harmonics. Verification of gained numerical results with available experimental data is carried out.