Thermophysics and Aeromechanics最新文献

The experimental results on the structure of the two-phase “liquid metal-gas” medium in vertical channels depending on the gas flow rate and channel diameter are presented. Lead-bismuth melt at a temperature of 160°C was used as a liquid medium, and argon was used as a gas phase. Data were obtained on the shape of gas bubbles, temporary changes in the gas content in channels, histograms of gas content distribution, and features of the slug flow of gas in the metal melt.

The results of an analytical solution to the problem of heat distribution inside a massive solid sample with concentrated heat supply to this sample surface are presented. Analytical expressions for the non-stationary temperature distribution inside the body are obtained using the integral cosine Fourier transform and the Hankel transform. Examples of solution application for estimating the characteristic times of reaching the Chernov points Ac₁ and Ac₃ in model hypoeutectoid steels under the effect of laser radiation are presented. The application of this solution to calculating the cooling dynamics of ceramic Al₂O₃ and SiO₂ samples, affected by the air and water jets, is demonstrated.

Gas atomization is the major approach for production of metal powders. This method gives up to 70 % of the entire metal powder production. However, modern trends demonstrate new requirements to the particle size distribution. This drives the development of new methods for power production. In this study the plasma-jet atomization method was presented.

The flow around a stationary gas Taylor bubble at downward flow velocities from 0.15 to 0.3 m/s in a vertical tube with a diameter of 20 mm was experimentally and numerically studied. Three-dimensional calculations were performed using the VOF (volume of fluid) method in the OpenFOAM package with application of the unsteady k–ω SST turbulence model. Hydrodynamic characteristics of the flow were experimentally studied using the electrodiffusion method. The effect of flow velocity on the change in the shape of the gas Taylor bubble nose was shown. The calculated and experimental data were compared and their good agreement was shown. The distribution of velocities in liquid and gas was studied as well as the distribution of the liquid film thickness around a gas Taylor bubble. It is shown that the wall shear stress in the liquid film around a gas Taylor bubble does not depend on the downward flow velocity.

This article presents the results of numerical simulation of heat transfer between a laminar axisymmetric methane/air flame and a cold flat wall. The simulation is performed for different distances between the nozzle exit and the surface, namely, for one, two, and three burner nozzle diameters. The flow evolution is calculated by the direct numerical simulation method with a detailed kinetic mechanism GRI-MECH 3.0. At a distance of three diameters, there is a significant reduction of heat flux close to the stagnation point due to a local recirculation zone formation between the flame cone and the wall. This phenomenon explains the observed decrease in local heat transfer. The obtained numerical results well agree with the previous flame study by planar optical methods.

Velocity fields and air flow structures have been experimentally established in a local working area with a horizontal panel heated by a gas infrared emitter in the modes of free and mixed (during operation of the air exchange system) convection using the optical SIV (Smoke Image Velocimetry) method. The analysis of the influence of the structure of the air flow, resulting from the heating of surfaces located in the local working area, on the formation of air velocity fields in the operating conditions of a gas infrared emitter was carried out. The extent of the influence of the convection regime on the aeromechanics of the local working area heated by a gas infrared emitter has been established.

A method and results of computing a laminar-turbulent flow past a swept wing under a control action generated by a source of blowing or suction from the model surface are presented. Pioneering results on the influence of three-dimensional blowing and suction sources on stability of the boundary layer on a swept wing and distributions of N-factors of various mechanisms of the laminar-turbulent transition aimed at changing its position are obtained by using the LOTRAN 3 software package.

The paper presents the experimental results on transient nucleate boiling on the heater surface with rapidly increasing surface temperature. According to the results of high-speed video recording with a frequency of 180 000 frames per second and a spatial resolution of 5.5 urn per pixel, the input data for existing models of heat transfer during nucleate boiling must be refined to take into account the existence of cluster and pulsating bubbles. It has been established that bubbles, interacting through the exchange of momentum, heat and vapor mass, accelerate activation of neighboring vaporization sites, so the clusters of bubbles can form at the initial stage of covering the heater surface with vapor. The main characteristics of single, cluster and pulsating bubbles have been studied for the wall superheating from 0 to 14 K above the temperature of nucleation beginning and flow subcooling from 23 to 103 K.

The influence of a thin layer of phase change material (PCM) on the thermal characteristics of the outer wall of a building made of lightweight thermal insulation material was studied numerically. Changes in temperature and heat flux density were analyzed for various locations of a PCM layer in the wall. It is shown that the use of a thin paraffin layer 4 mm thick in a wall made of foamed polyurethane 100 mm thick can reduce the amplitude of heat flux fluctuations on the inner surface of the wall in the summer from 2 to 13 times, depending on the PCM location. The greatest reduction is achieved when installing the PCM in the central area of the wall. Calculations show that when using a PCM in the walls of buildings made of light thermal insulation materials, a positive effect, associated with a 6–8 hour delay in the maximum heat flux entering the room relative to the maximum daily value of the outside air temperature, is observed in the summer.

The paper describes the results of an experimental study of the influence of control surfaces and fuselage on the structure of a separated flow around a model of a small-size unmanned flying vehicle with a straight leading edge of the wing. The use of oil-soot visualization and hot-wire anemometry shows that the separation region location depends on the attitude of control surfaces, while the presence of a fuselage leads to reduction of the critical angle of attack.