Home – Home – Jornals – Advanced Search

In the statistical solution to problems of analysis, synthesis and filtration for systems of the diffusion-discontinuous type, it is required to simulate an inhomogeneous Poisson point process. To simulate the latter, an algorithm is sometimes used based on the property of the ordinariness of the process. In this paper, a modification of this algorithm is constructed using an efficient method for modeling random variables. The statistical adequacy of the method developed was checked by solving test problems.

Microfluidic liquid-liquid flows exhibit a wide range of different flow patterns. The most important point in practical applications is the transition from the segmented to the continuous flow patterns, as well as the prediction of this transition for an arbitrary combination of fluids. This paper presents a detailed analysis of the existing experimental data on flow patterns of immiscible liquids and provides data generalization through dimensional analysis. It is shown that the previously proposed criterion (We^0.4Oh^0.6) composed from Weber and Ohnesorge numbers provides a prediction on transition continuous-to-segmented flow with good accuracy if viscosity ratio λ = m _d/ m _c is less than unity. For the viscosity ratio λ > 1 this criterion ceases to work, and additional experimental data are required to construct a generalizing parameter for microfluidic flow in such systems.

The present study aims at obtaining the optimum contoured crater for a cylindrical-based film cooling hole with maximum area-averaged cooling effectiveness via computational fluid dynamics and optimization method. The influences of 5 geometrical parameters, which depict completely the dimensions of the contoured crater, were discussed through performing the orthogonal experiment design and range analysis. The optimum designs at blowing ratios of 0.5 and 1.5 were obtained by using the range analysis and the genetic algorithm combined with back propagation neural network respectively. From the analysis of the results, it can be found that the latter optimization method outperformed with higher area-averaged cooling effectiveness at both blowing ratios. The area-averaged cooling effectiveness of the optimized cratered holes were improved by 17.21 % at blowing ratio of 0.5 and 101.96 % at blowing ratio of 1.5, respectively, compared to those of the reference geometry. The improvements on the film-cooling performance were explained in terms of the flow filed and the vortex structures.

The wetting of a surface with a combined texture is investigated. Contact angles are measured for various surface textures. The method for hydrophobic texture formation using a combination of mechanical punching and patterning the surface made on the basis of polymers and aluminum oxide nanoparticles is proposed and analyzed.

The regularities of liquid film formation in the vicinity of capillary holes of a die when starting the droplet generator, as well as the regularities of film rupture and the formation of jets on its surface are experimentally and theoretically investigated. It is shown that the transient processes of film formation and rupture last several seconds, and the defining mechanism of film rupture is the development of bending instability of the jet nucleus.

The paper presents a problem of one-dimensional flow of water and steam separated with an interface; the flow is arranged in an inclined porous layer and subjected to lateral heat flux. The analytical stationary solution was found and the properties analyzed. Instability of flow for a certain region of parametric space was found and the nature of instability was described.

In this paper, energy and exergy analysis has been done for irreversible Brayton cycle with regenerator, reheater, and intercooler. In this work, the influence of the different parameters such as the efficiency of cycle's components surveyed based on the first and the second laws of thermodynamics. The lost exergy in the different components and the total lost exergy of the irreversible Brayton cycle are calculated under several conditions. Also, the optimum pressure of the intercooler and the reheater are obtained under different conditions. To obtain the optimum pressure, irreversible Brayton cycle with regenerator, reheater, and intercooler is simulated in engineering equation solver software and optimum pressure is obtained based on the first and the second laws of thermodynamics in each simulation. The obtained optimum pressures are compared with the geometric mean of the low and the high pressure of the cycle in each simulation.

Results of a numerical study of ignition of a cold supersonic (М_jet = 1.46) hydrogen jet surrounded by an annular supersonic (M_air = 1.86) jet of hot vitiated air expanding into a submerged space are reported. The simulations are performed under the experimental conditions of Cohen and Guile (1969) based on the Reynolds-averaged Navier-Stokes equations supplemented with the k-w SST turbulence model, a detailed kinetic mechanism of hydrogen combustion in air, and various models for taking into account the turbulence-chemistry interaction. The calculations are performed in the ANSYS Fluent 2020 R1 software in a transient two-dimensional axisymmetric approach by using a pressure-based solver. The instantaneous, mean, and RMS components of the main aerodynamic parameters and species mass fractions are obtained. A detailed comparison of the calculated profiles of the Mach number, total temperature, and species mass fractions along the jet axis and in several jet cross sections for non-reacting and reacting flows with experimental data is performed, revealing reasonable agreement in all parameters. It is demonstrated that the use of the transient approach combined with a detailed kinetic scheme makes it possible to reproduce the vortex structures developing at the combustion layer boundary, which make a significant contribution to hydrogen-air mixing, and, thus, affect the hydrogen combustion process.

The article presents experimentally obtained temperature dependences of the degree of blackness of metals of group VIII of the periodic table: cobalt, nickel, palladium and platinum.

Using the methods of mathematical modeling in a single-phase formulation of the Stefan problem, the problem of melting of an ice layer, which scatters radiation, was formulated and solved. To solve the radiation part of the problem, a modified method of mean fluxes was used. Anisotropic scattering was taken into account using the method of expansion of the scattering indicatrix in terms of Legendre polynomials. The influence of the scattering direction on the rate of ice layer melting is shown. Satisfactory agreement of the calculation results with the experimental data and with the data of calculation by the transport method has been obtained.