Thermophysics and Aeromechanics最新文献

This review deals with the formation of solid carbon (in particular, soot) under various conditions of methane conversion: pyrolysis, diffusion flame combustion, steam reforming, conversion in supercritical water and high-pressure water-oxygen fluid. Particular attention is paid to the consideration of the carbon formation conditions at high pressures; the goal is to identify the parameter regions with a lack of experimental information or its insufficient presentation, but where carbon formation is very likely. When designing the equipment with continuous operation, it is necessary to know the corresponding parametric boundaries of the areas of solid carbon formation in order to avoid emergency situations and/or to reduce depreciation costs.

Optical diagnostics of the three-dimensional structure of large eddies in the near zone of a turbulent jet (at Re = 5000) exhausting from a round nozzle is performed in the case with coaxial periodic disturbances of the flow through annular slots at the nozzle edge and through holes in the internal surface of the nozzle in the transverse direction. The external action leads to rapid turbulization of the flow near the nozzle edge due to generation of large extended toroidal vortices in the case of coaxial disturbances and due to significant reconstruction of the flow with rapid disintegration of the jet core in the case of transverse disturbances.

Experimental results of the process of combustion after single-spark and two-spark ignition of a stoichiometric propane-oxygen mixture within a test tube with the length of 170–860 mm and internal diameter of 5 mm are presented. It was found that in the area between two spots of ignition the slowing down for two combustion propagation fronts occurs and followed by front acceleration. These processes occur due to generation of oncoming gas-dynamic flows and accompanied by mutual boost of spots in the form of “spark plasmoids” that activates combustion. It was found in experiments that the electric-discharge-spark plasmoids are the key parameters for the process of ignition and combustion of a propane-oxygen mixture in a test tube.

A numerical analysis is performed for heat and mass diffusive convection generated by radial temperature and concentration gradients across two verticals coaxial rotating cylinders with imposed axial laminar flow. The internal rotating cylinder is brought to a high temperature and concentration, while the outer motionless cylinder is exposed to a cold temperature and low concentration. The D2Q9 model of the lattice Boltzmann model is used to simulate the flow field, while the temperature and concentration fields are computed by the D2Q4 model. It has been shown that when the Reynolds number is in the range of [6–10], we note an increase in the wavy flow structure in the duct, and Taylor cells disappear in the annulus. For fixed high values of Ra in the range of [300–500], different flow regimes are observed. So, by increasing the Rayleigh number again (Ra > 550), the flow is a basic thermo-solutal convective flow symbolized by a large double-convective cell installed throughout the domain.

The object of this study is a straight rivulet flowing over an inclined plate whose surface is covered with regular nonlinear waves. Such waves can be modeled in full three-dimensional statement, but it is also possible to use a simplified quasi-two-dimensional approach with self-similar shape of rivulet cross section. In this study we directly compare the results of two- and three-dimensional approaches to the shape of the wave rivulet surface reconstructed experimentally using the laser-induced fluorescence technique. It is shown that the three-dimensional model reproduces well the wave surface of a rivulet, including such three-dimensional peculiarities as the wave front curvature and minor perturbations of its rear slope. Though the two-dimensional model is unable to reproduce such peculiarities, it describes well the parameters and shape of a wave in the central longitudinal section of the rivulet.

Results of an experimental study of the evolution of a vortex flow formed under the action of a submillimeter arc discharge moving in a constant magnetic field in a supersonic air flow near a flat surface are presented. Owing to the high reproducibility of the discharge parameters and precise synchronization of the equipment, it is possible to study the flow structure in much detail by the methods of particle image velocimetry and Schlieren visualization. It is found that the spatial and temporal characteristics of the generated vortex structures can be effectively controlled by changing the direction of the electromagnetic force arising during the discharge.

Within the framework of lubrication theory, numerical studies of thin film movement along the surface of a wing with the NACA0012 airfoil were carried out. The film is created by incoming drops of water and drifted by the external air flow. A model problem of one-dimensional film motion in the presence of a retarding longitudinal stress caused by disjoining pressure is considered. A cubic equation was obtained to determine the film thickness. If the contact angle exceeds a certain critical value, then the solution of this equation loses its physical meaning at some distance from the front critical point (the film thickness becomes negative). This means that the one-dimensional flow assumption is no longer satisfied. The maximum coordinate for existence a one-dimensional solution can be considered approximately as the beginning for the film disintegration into rivulets. Theoretical results are compared with the available experimental data.

Implementation and application of the AUSMPW+ solver for computing inviscid flows at the control volume face in the HyCFS code on a structured grid are discussed. It is shown that the use of AUSMPW+ allows the carbuncle formation in the flow around a cylinder to be successfully prevented.

Simulations of flows with boundary layer separation by using the AUSMPW+ solver leads to results that coincide with those obtained by the HLLC solver. The pressure and heat transfer coefficients for a double-cone model predicted by HyCFS coincide with the experimental data of LENS-XX with the same accuracy as the results of other researchers computed by independent numerical codes.

Thermal resistance circuits are widely used to model heat transfer in a stationary solid under steady state conditions in one or two dimensional systems. For a moving solid, the convection mode of heat transfer with the Eulerian/Lagrangian point of view can be considered to model the heat transfer. In this research, heat transfer through a rotating circular cylinder is investigated and modeled using the thermal resistance circuit. Heat enters the cylinder from a constant high temperature boundary at the outer or inner surfaces of the cylinder, respectively. The width of this boundary corresponds to angles 15, 30, 45, 60, 75, or 90 degrees. Heat is exited from the other side of the cylinder on its outer surface at the same angular width as the high temperature boundary. The effect of different parameters such as rotation speed, cylinder thickness and angular width of constant temperature boundaries is investigated. Different models of heat transfer as circumferential conduction, radial conduction, moving fin and semi-infinite are proposed to estimate the rate of heat transfer through the cylinder and a correlation has been proposed for each of them.

When the surface clearance is less than 100 times of the thickness (normally on the 1 nm scale) of the adsorbed boundary layer in a hydrodynamic thrust bearing, the effect of the adsorbed boundary layer should be considered. The RMS roughness of the classical bearing surface is normally on the scales of 0.1–1 µm, while that of the micro/nano bearing surface is normally at least on the 1 nm scale. For whichever bearing, when the bearing clearance is so low that the effect of the adsorbed boundary layer should be considered, the effect of the surface roughness of the bearing should also be considered. The present paper presents the multiscale calculation results for the surface roughness effect in the hydrodynamic wedge-platform thrust bearing with small surface clearances. It was found that in the studied model of the bearing the hydrodynamic pressure as well as the carried load of the bearing are significantly increased with the increase of the surface roughness; this is due to the effect of the adsorbed boundary layer. The findings is new and has an important implication to the modeling of mixed lubrication with small surface clearances.