Thermophysics and Aeromechanics最新文献

A lattice model of the pore space of a microsphere packing and a method for calculating the microstructure of a two-phase flow, taking into account the topology of pores, are proposed. The sequence of filling the pore contractions and expansions with drainage and imbibition of phases and the dependence of capillary pressure on saturation of phases and the coefficient of longitudinal dispersion for transfer of a dissolved substance were obtained under conditions of the determining influence of capillary forces.

A possibility of using non-monochromatic photodetectors registering radiation in a wide range of wavelengths as sensors of the brightness channel in spectral-brightness pyrometry is considered. A definition of the effective wavelength for a pyrometer is introduced based on a dependence of the registered signal on the temperature of thermal radiation source. Experimental results on determining the effective wavelength of the photodetector with the sensitivity in the interval of wavelength 400–1100 nm for recording the temperature lamp radiation in the temperature range from 1557 to 2494 K are reported.

NO_x emissions from gas boilers pose a significant threat to air quality. To significantly decrease NO_x emission level from the gas boiler exhaust, a novel nitrogen reduction combustion method is proposed that combines air-staging with humidification combustion techniques. A comprehensive study was conducted using CHEMKIN software to analyse the nitrogen reduction performance and sensitivity in various compound modes. The impact of combustion temperature, excess air coefficient, and injection position of over-fire air on the nitrogen reduction performance in the optimal compound mode was investigated. The results showed that the nitrogen reduction effect of the compound mode was better than that of the pure staged combustion mode. Compared with pure staged combustion, humidifying the main combustion zone could improve the nitrogen reduction rate by 4.9 %, which was 1.7 % higher than humidifying the burnout zone. The most significant nitrogen reduction effect was achieved when both combustion zones were humidified, leading to a 7.4 % increase in the nitrogen reduction rate. Further, by humidifying both combustion zones and reducing the combustion temperature, the emission of NO during boiler operation was found to be reduced significantly. The nitrogen reduction rate can be increased to 65.7 %, which is 22.1 % higher than that of the single air-staging.

In transonic flight, the phenomenon of transonic buffet arises due to the shock-wave/boundary-layer interaction. To mitigate the effects of transonic buffet while maintaining the lift-drag ratio, a passive buffet control approach utilizing a trailing-edge buffet breather is proposed, based on an analysis of the pressure distribution on a supercritical airfoil. The control effect of the trailing-edge buffet breather and its correlation with breather width, outlet position, and freestream Mach number are analyzed with the unsteady Reynolds-averaged Navier–Stokes (URANS) method on the OAT15A airfoil. Findings suggest that the separation flow behind the shock wave on the suction side of the airfoil is isolated from the separation region at the trailing edge by the buffet breather, impeding the fusion and interaction of these flows and thereby suppressing the transonic buffet. The control effectiveness of the buffet breather can be substantial when the outlet is positioned appropriately downstream of the shock wave. A wider breather width results in a stronger jet intensity, improving control of flow field unsteadiness but with a trade-off of increased lift loss. Furthermore, the control method exhibits efficacy at various Mach numbers, with minimal impact on lift-drag characteristics.

The synthesis of diamond coatings on silicon substrates using a gas-jet method with application of a high-speed jet to transport a gas mixture, activated in a microwave discharge, is studied. The coatings are synthesized from a mixture of hydrogen, methane, and argon. The possibility of maintaining the integrity of the silicon substrate under conditions of gas-jet deposition at high temperatures is shown. The rate of diamond synthesis on a silicon substrate exceeded the rate, achieved earlier in gas-jet experiments with activation in microwave plasma without adding argon, as well as during deposition from a hydrogen-methane-argon mixture at lower substrate temperatures.

Considering that the experimental investigations are generally conducted under conventional pressure and temperature conditions, to make the research results applied reasonably under practically high-pressure and high-temperature environment wherein the hot-section component works, a similarity theory was conducted on the laminated cooling structure to observe its overall cooling effectiveness on the hot-side surface. Based on the simplified one-dimensional heat transfer model of film cooling plate, a corresponding similar relationship for the overall cooling effectiveness was established. From this similarity relationship, the main non-dimensional parameters were deduced and analyzed, including the adiabatic cooling effectiveness, hot-side Biot number, hot-side Nusselt number, and the ratio of convective heat transfer coefficient. By reasonably selecting the characteristic scale and the material thermal conductivity of the tested model, a similarity strategy method was proposed to ensure that the overall cooling effectiveness measured under experimental and actual working conditions is approximately the same. The above-mentioned approach similarity strategy was numerically validated through two randomly-selected groups of laminated cooling structures.

To study the aerodynamics of a pulsating flow in a flat channel of 20×150×600 mm, an experimental setup has been constructed. Gas flow pulsations were generated by rotating a damper that completely blocked the channel. The damper was located behind the test section, and the setup operated in the regime of sucking air from the surrounding space. These studies were carried out using the PIV method, synchronizing the measuring system with the damper rotation angle. The experiments were carried out at pulsation frequency F = 8 Hz. The experimental results are directly compared with the case of a steady flow with a fixed damper, but with the same rotation angle as in the case of phase averaging. It has been established that under these conditions, superimposed flow pulsations weakly affect the longitudinal velocity profiles, integral characteristics of the wall layer and friction coefficient, which indicates a quasi-steady flow in the channel.

Data on the structure of flow seeding with particles in a supersonic wind tunnel with electric arc heating of the working fluid are reported. Velocity profiles near the plate surface have been obtained. The dependence of the spectral characteristics of heterogeneity of particle seeding in the boundary layer on the Reynolds number and flow regimes is shown. The possibility of isolating the anisotropic component of the heterogeneity field of particle distribution in the laminar boundary layer of the plate is presented.

Results of an experimental study of gold-induced crystallization of thin films of amorphous germanium (a-Ge) are reported. The Raman spectroscopy and optical microscopy are applied to study the influence of the initial thickness of the a-Ge film on the morphology of the material obtained by means of annealing of bilayer Au/a-Ge structures. The a-Ge/Au thickness ratios equal to 1.1 and 2.3 are considered. Low-temperature annealing of quartz/Au/a-Ge samples is performed in a high-vacuum atmosphere (10⁻⁴ Pa) at a temperature of 300°C for 24 h. The Raman spectroscopy results show that sample annealing leads to complete crystallization of a-Ge with formation of polycrystalline germanium (poly-Ge) in both bottom and upper layers of the samples. For the sample with a-Ge/Au = 2.3, a continuous poly-Ge film is obtained on the substrate due to implementation of the layer exchange mechanism. In this case, poly-Ge hillocks are formed in the upper layer of the sample due to a-Ge crystallization in the presence of Au. For the sample with a-Ge/Au = 1.1, a non-continuous poly-Ge film with a coverage degree of 30 % is formed in the bottom layer. The poly-Ge material is formed in the upper layer due to the processes of “explosive” crystallization and secondary crystallization induced by Au.

Aircraft icing seriously threatens flight safety, thus studying its quantitative properties can provide a deep understanding of how icing occurs and how to treat it. In this paper, methods of 3D modeling for ice micro-structure and ice density calculation are proposed based on wind tunnel experiments. Firstly, a variational segmentation method is presented to extract the quantitative information of icing pores, and stochastic analysis of pores characteristic is implemented. Then a 3D model of the micro-structure is established based on the specific assumptions and the micro quantitative formation. Finally, the icing density can be easily obtained by the mixture density calculating method. In the experiments, the 3D modeling results of icing micro-structure and density calculation results under different icing conditions are given, which demonstrate the effectiveness of the proposed method. Furthermore, the influences of two parameters in the density calculation are analyzed to give a clear understanding of how the parameters work.