Thermophysics and Aeromechanics最新文献

The action of a pair of weak shock waves on a supersonic boundary layer on a swept flat plate with a bluntness radius of the leading edge equal to 2.5 mm at the Mach number 2 is experimentally studied. Transverse hot-wire measurements are performed in the boundary layer with a fixed distance of the probe from the model surface. It is found that a change in the sweep angle of the leading edge from 35 to 45 degrees reduces the intensity of the action of the weak shock waves on the boundary layer flow. As the sweep angle of the leading edge increases to 50°, the weak shock waves no longer affect the flow in the supersonic boundary layer on the swept plate.

The Cr-Ag coating was prepared by electroplating and magnetron sputtering on 6061 aluminum alloy matrix to balance the thermal shield radiation shielding capability and the coating performance for the International Thermonuclear Experimental Reactor (ITER) project. The microstructure, adhesion, and thermal shielding properties of the coating were analyzed. The results show that the Cr-Ag magnetron sputtering coating has flat surface, and better thickness uniformity than electroplate coating. The adhesion force of the Cr-Ag magnetron sputtering coating is 1.56 times higher than that electroplating coating, which is 53 N. The emissivity test results show that the emissivity of Cr-Ag coating by magnetron sputtering method at 80 K is 0.018, much lower than the emissivity of electroplating coating and 6061 aluminum alloy matrix. Theoretical calculation of radiant heat load based on emissivity test shows that the thermal shielding effect of Cr-Ag coating on thermal shield surface by magnetron sputtering is better than that of other groups. The results are of great significance for the combination of coating properties with broader thermal shield properties.

The work is devoted to modeling the disturbance propagation in viscous incompressible laminar boundary layers, using linearized equations for disturbance amplitudes. Along with the numerical model based on original linearized equations, the article considers three models based on equations derived from the original ones by neglecting the streamwise pressure gradient, or the streamwise viscous terms, or both. The models are compared numerically by the example of generation and propagation of disturbances in the boundary layer over a slightly concave plate. Conclusions are drawn about the feasibility of the same simplified models to adequately simulate both Tollmien–Schlichting waves and Görtler vortices in a range of practically important parameters.

Numerical studies of aerodynamics and heat transfer in a vortex burner during flame oxygen combustion of pulverized coal are presented. The proposed numerical method has been tested using experimental data on oxygen combustion of coal in a flow. The influence of oxygen concentration in the blast on the processes of ignition and combustion of coal dust in a nitrogen-free environment has been considered. It has been established that for the burner under study, an increase in oxygen concentration from 40.1 to 66.7 vol. % leads to a change in the flow structure, an extension of the flame size, and an increase in the average value of unburned solid carbon concentration from 0.00136 to 0.4 g/m³ at a distance of 1.5 m from the burner.

The effect of a passive control concept made of a porous surface with a cavity underneath the shock wave/boundary layer interaction on a supercritical RAE-2822 airfoil in a transonic flow regime, is investigated to achieve a better efficiency using a variable porous length with a low permeability factor. A numerical approach is carried out using the commercial ANSYS Fluent code to solve the Reynolds-averaged Navier–Stokes equations of a two-dimensional, fully turbulent, compressible, and steady flow around the airfoil at M_∞ = 0.82, Re_∞ = 2·10⁷, and a 6° angle of attack, with the Spalart–Allmaras turbulence model. Both cases of a clean and a porous configuration, have been studies. The results showed the effect of the control technique by producing a downstream movement of the shock with a larger flow supersonic region and a reduced flow separation zone and thus a weaker SBLI, compared to the clean. Consequently, a lift increase and a drag reduction are obtained, leading to an improvement in the aerodynamic efficiency. Seeking for a higher control efficiency, variable porous surface lengths and low permeability factors, have been tested. The best aerodynamic efficiency was obtained with a full-chord porosity and a low permeability factor of 10⁻⁶, with an appreciable gain in lift of 47 % and a substantial net drag reduction of 65 %.

The thermal instability experienced by aircraft beyond supersonic speeds poses a significant risk to structural stability, particularly due to airfoil surface delamination. Conventional methods of addressing this issue involve incorporating thermal shields and modifying the design, but these approaches require extensive redesigning and lack scalability. However, an alternative approach is to reduce surface temperature distribution and minimize surface drag through the application of nanomaterial coatings. In this study, graphene nanocoating was utilized to reduce the surface roughness of the TsAGI S-12 airfoil. The thermal characteristics of the coated airfoil were evaluated using infrared (IR) imaging. The results of wind tunnel experiments showed a remarkable 21 % reduction in surface temperature and an 18 % reduction in shock wave angle compared to the conventional airfoil. Additionally, atomic force microscopy (AFM) analysis of the coated nanomaterial surface revealed a decrease in surface roughness from 20 nm to 2 nm. The use of nanomaterial surface coatings proves to be a simple and highly effective method for reducing surface temperature and minimizing shockwaves. Moreover, it offers the advantage of high scalability, making it easily applicable in the aircraft industry. Ultimately, the application of nanomaterial coatings has the potential to revolutionize the supersonic aviation industry by enhancing stability and performance.

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.