Home – Home – Jornals – Thermophysics and Aeromechanics 2026 number 1

The effect of a compliant coating (film) over a porous surface on the stability of a supersonic (M = 2) boundary layer on a flat plate to disturbances of the first mode of instability under the conditions of experiments in the T-325 wind tunnel was calculated using linear stability theory. The calculations showed that a porous coating with a thin-film membrane on the surface can stabilize the boundary layer at Mach number M = 2 at the frequency most increasing on a solid plate. The dependences of the rates of the spatial growth of disturbances on a number of factors were found. Nonmonotonic (with minima) dependences of these growth rates on film tension, pore radius, porous coating depth, and porosity were obtained. The spatial growth rates of disturbances decrease with decreasing film thickness and the ratio of the gas pressure inside the pores to the static pressure in the boundary layer. It was found that stabilization of a supersonic (M = 2) boundary layer relative to the case of a smooth impermeable plate can occur only with a film thickness of less than 18 nm.

The paper presents experimental results from a study on supersonic flow across a cylinder. Selected measurements of pressure on the cylinder surface were taken. Different variants of jet blowing were tested with a focus on variation in the pressure distribution on a surface. The difference between variants was in positioning the blowing hole on the cylinder circumference in the mean cross-section. The paper describes the influence of the hole position on the pressure distribution for a case of interaction between a supersonic free stream and a jet. New experimental data on a pressure distribution on a circular cylinder surface with at different positions of the blow hole are now available.

Experimental data on the nature, thermophysical parameters, and boiling modes of closed two-phase evacuated water-filled thermosyphons are presented, and their application prospects are discussed. The high efficiency of thermosyphons in slug and hyperslug modes is experimentally confirmed.

Bubble motion in an inclined circular pipe with a cocurrent liquid flow was experimentally studied. The effects of low concentrations of surfactants, the channel inclination angle, and the flow velocity on the size of gas bubbles and their ascent velocities were determined. It was found that the combination of liquid flow and surfactant significantly suppresses bubble coalescence. For the given conditions, the drag coefficient of a bubble rising near the wall was calculated. It was shown that the drag coefficient is inversely proportional to the Weber number both in pure water and with the addition of surfactant.

The article studies the intensification of heat transfer during cooling of a surface modified by laser treatment with a dispersed coolant flow. A laser ablation technique using a pulsed laser is described, leading to the formation of craters up to 600 μm in diameter on a copper surface with the following roughness parameters: Ra = 1.48 μm, Rz = 9.8 μm. The results show an increase in the removed heat flux by 35-40%, the heat transfer coefficient by 38-55% in the intense boiling mode (115-125 °C) compared to the unmodified surface. The proportion of heat removed due to the phase transition reaches 90% at a removed heat flux density of 8.4 MW/m², on the modified surface.

The development of non-stationary thermal gravity-capillary convection in a layer of ethyl alcohol with a free surface after sudden electric heating of one of the vertical walls of a rectangular cavity was experimentally studied. The effect of a heated liquid flow along the free surface onto the opposite thin metal wall of the cavity was studied. The influence of the liquid layer heights and heat flux densities on the heated wall of the cavity was investigated. Temperature fields on the thin wall and on the free surface of the liquid layer were measured using a FLIR x6530sc thermal imager. Computer processing of thermal imaging films allowed the construction of distributions of temperature and temperature gradients along the wall height depending on time. The amplitude-frequency characteristics of temperature pulsations associated with the occurrence of secondary flows in the heated liquid flow on the wall were determined, and their effect on instantaneous temperature fields on the wall was studied against the background of a monotonic change.

Multi-rotor aerial vehicles have the rather short history of active usage, so many aspects of vehicle aerodynamics remain poorly investigated. One of these aspects is a problem how the rotor-generated flow affects the elements of framework ad body of a multi-rotor copter. The paper studies the influence of rotor rotation on the aerodynamic drag coefficient and the sideforce acting on the body of a meteorology drone (body with a spherical shape). Calculations were performed in the RANS statement with a direct account for the rotor rotation. Numerical results are verified on the base of PIV-measurements. The aerodynamic characteristics of the quadcopter body depend significantly on the unsteady flow generated by the rotors.

Some properties of vortex filaments in a weakly nonideal countercurrent Bose-Einstein condensate (BEC) are described. This paper focuses on the study of reconnection processes and the equations of motion. One of the motivations for this study is that the dynamics of quantum vortices in superfluid helium has been obtained at the phenomenological level, and a number of questions requiring clarification can be addressed by studying the corresponding problem in BEC. Considering a vortex filament as the intersection line of surfaces where the real and imaginary parts of the macroscopic wave function ψ(r, t) vanish allowed us to write an equation of motion for the vortex filament. Remarkably, the structure of this equation completely coincides with the structure of the equation for the dynamics of a vortex filament in superfluid helium, which was derived from entirely different, phenomenological considerations.

The dynamics of surface temperature changes for a water droplet resting on a structured black silicon substrate heated to 90°C were studied. The wetting properties of black silicon were analyzed during substrate heating in the temperature range of 30-90°C. Thermal imaging studies revealed that vapor nucleation sites form at temperatures close to the boiling point at the liquid-black silicon interface. The dynamics of temperature changes on the surface of a thin liquid droplet during the final stages of evaporation were studied, including the formation and subsequent development of bubble nuclei within the droplet. Convection and bubble formation were shown to result in non-uniform temperature fields.

This study is aimed at improving environmental efficiency by establishing the dependence of the parameters of optimal combustion of liquid hydrocarbon fuels (diesel fuel, crude oil, fuel oil, kerosene, waste oil) on their physical properties using steam atomization with superheated steam. The methodology includes the construction of regime maps of CO concentration with approximation by radial basis functions and smoothing by a median filter. During the study, a statistically significant linear relationship between the angular coefficients of the optimal regime equations and the Laplace number (r = 0.834, R2 = 0.7) was established. Based on the obtained dependences, an equation is proposed to calculate the optimal flow rate of superheated steam depending on the Laplace number for the optimal combustion mode of liquid hydrocarbon fuels in an atmospheric burner with steam atomization and a gasification chamber to reduce emissions of harmful substances.

An installation was designed, fabricated and studied for methane pyrolysis and hydrogen production. Methane heating and pyrolysis occurs by burning a fraction of methane-hydrogen mixture (60 % hydrogen and 40 % methane) produces by pyrolysis (a return for the plant demand). The installation thermal design was performed with the account for the heat consumed fro pyrolysis, insulation heat loss and flue gases loss. The study determined the plant heat power and the efficiency coefficient. Usage of methane-hydrogen mixture as fuel allows reducing the CO₂ emission as compared to known methods of hydrogen production.

Using the integral heat balance method, analytical solutions were obtained for the formation of dynamic and thermal boundary layers in a methane pyrolysis (thermal decomposition) reactor with variable viscosity and thermal diffusivity within these layers. It is shown that, on the inner surface of a metal reactor wall heated to 1000°C, a layer of stagnant gas forms due to high viscosity and thermal diffusivity, having the same temperature as the wall. Isotachs and isotherms in this layer are located perpendicular to the wall surface. In this case, boundary layers form at a certain distance from the wall, within which the velocity is practically zero and the temperature is equal to the wall temperature, significantly exceeding the gas temperature outside the boundary layers. In the near-wall layer of stagnant gas at high temperatures, intensive carbon formation (pyrolysis graphite) occurs, depositing on the reactor walls until the reactor flow cross-section is completely carbonized and the pyrolysis process stops.

To create an efficient microchannel reactor for hydrogen production, steam reforming of carbon monoxide in a slotted annular channel was experimentally studied. The microchannel reactor is formed by a submillimeter gap between two cylinders, with a catalyst applied to the outer side of the inner cylinder. Platinum applied on cerium oxide was used as a catalyst. The thermal characteristics of the shift reaction with the formation of carbon dioxide and hydrogen were experimentally studied. Experiments were carried out at a steam-to-carbon monoxide ratio of 3:1 at different mixture flow rates. It was shown that a fourfold increase in the mixture flow rate leads to a significant increase in the temperature difference between the reactor inlet and outlet, caused by the heat release of the reaction (from ΔT ≈ 20°C at a contact time of 189 ms to 80°C at a contact time of 46 ms). According to analysis of the composition of the outgoing gas, with an increase in the mixture flow rate, the degree of carbon monoxide conversion decreases significantly.

The paper presents the direct numerical simulation for a laminar flame of a premixed methane-air mixture using a detailed kinetic mechanism. During this study, the numerical module laminarSMOKE is supplemented by a problem of conjugated heat transfer between the flame and nozzle walls. A change in the isothermal boundary condition on the nozzle wall influencing the conjugated heat transfer condition results in a higher temperature of the temperature of the nozzle front edge, reduction in the flow density gradient near the nozzle boundary and a reduction in the low-frequency oscillation of flame caused by the buoyancy effect.

A study on transition processes for experimental time dependencies of the pitch angle for the case of free rotation of a body discovered the final intervals with a steady amplitude of oscillations - known as quasi self-oscillations. Statistical analysis demonstrated that the maximum possible difference between the amplitudes of self-excited oscillations (including the case of quasi self-excited oscillations) at the normalized oscillation frequency of 0.02 was about 1 degree.

A multiblock numerical model was used to study the phenomenon of vacancy formation in a chain of dust particles. Self-consistent spatial distributions of the space charge and electric potential around the dust particles for two cases were obtained by means of numerical calculations: a linear chain of five particles and a chain of four particles with a vacancy. The equilibrium charges of particles and the magnitudes of the main forces acting on them (the ion drag force, the Coulomb force of particle repulsion, and the force exerted by an external electric field on charged particles) were calculated. It was shown that vacancy formation, without changing the structural parameters of the chain, occurs under conditions of strong ion trails, with the fourth and fifth particles in the strong ion trail of the second particle.

This paper describes a new phenomenon of generating a stable double precessing vortex in a highly swirling turbulent flow. It also identifies the range of flow conditions providing the clearest observation of this effect. It also identifies key features of the internal flow structure and the kinematic scheme of the double vortex precessional motion. The geometric parameters of the helical vortex are measured depending on the flow regime. The obtained results are important not only from a practical standpoint for the possibilities of controlling the flow structure in industrial apparatuses, but also from the standpoint of fundamental problems in vortex dynamics. Precession of a helical structure represents a canonical case of self-induced motion of a vortex filament with a helical axis of rotation.

This paper presents the analysis of linear stability of a swirling flow in a model combustion chamber. The flow is characterized by a strongly coherent component corresponding to vortex core precession. Using averaged data obtained via the large eddy simulation, a global stability analysis was performed taking into account turbulent viscosity. A mode with a dimensionless frequency of 0.76 was identified in the eigenvalue spectrum. The eigenfunction distributions indicate that this mode corresponds to a precessing vortex core (PVC). The study confirms that the PVC is a global unstable mode developing in a mean turbulent flow and will serve as a basis for further work on the development of PVC control strategies.

The supercavitation cavities were studied in a slot channel with a wing-shaped body inside. The wing attack angle was 21°. The dynamics of tracing flat cavitation bubbles were studied using a high-speed camera. The methods of algorithmic diagnostics of two-phase flow were used to detect the size of bubbles, their velocity, direction of movement and spatial distribution. It is shown that there are three types of supercavitation cavities arising in slot channels: a transparent pulsating cavitation cavity with periodic vortex formation at the site of its closure; steam and a steam-water mixture coexisting inside the cavity; a cavity completely filled with liquid with tracing steam-gas bubbles inside. It is determined that the bubbles move into the supercavitation cavity from its boundaries to the center; further they move to the front of the cavity and merge with it. The maximum velocity of bubbles is half the velocity of the oncoming flow.

The emergence and development of a vortex system during the separation of a supersonic air flow on the rib of a dihedral model with face opening angle of 270° was studied in details. The appearance of a separation vortex above the lateral face was detected for a flow with an angle of attack α = 1º. For a case with α ∽ 2º, boundary layer separation occurs near the rib of angle-shaped configuration. With an increase in pressure drop between the top and lateral faces of the model, the separation flow size grows and at an angle α = 3.7º a new vortex form is observed (a secondary vortex). For a flow with an angle of attack α = 8º, a third vortex is clearly observed. This vortex is located above the secondary vortex and it has a minor influence on the pressure distribution and the limiting streamlines behavior on the lateral face. The flow at this angle of attack α results in repeated separations for thin boundary layers near the configuration rib and beneath the enlarged secondary vortex. Within the tested interval of the attack angle α = 8º - 24º , the sizes of those local separations remain almost the same. It was shown that analysis of limiting streamlines patterns and surface pressure distribution cannot fully elucidate the actual structure of complex vertical systems without gaining some additional data.

Theoretical models of aerothermochemical interaction between a flow surface and dissociated air are presented for the case of combustion and sublimation near the forward stagnation point of a blunt body. Research methods and results are generalized to obtain a solution based on the similarity method for the case of combustion and sublimation using graphite in arbitrary cross-sections of a cone, sphere, wedge, cylinder, plate, and spherically blunt cone under laminar flow conditions with high Reynolds numbers. For various geometric shapes in a wide range of hypersonic flow conditions, calculations of the mass flux, heat flux, and friction drag coefficient are presented, the results of which are linked by universal dependencies expressed in terms of the stagnation enthalpy, pressure, velocity gradient, pressure gradient parameter, and surface temperature.

Thermal conductivity of solid magnesium-lithium alloys with X_Li = 35, 40, 50 at. % in the temperature range of 80 - 350 K was measured by a transient method using a plane heat source. The obtained results were compared with literature data for alloys of other compositions. For all the studied alloys, anomalous behavior in the form of a kink in the range of 310 - 330 K and a feature near 240 K, presumably associated with a martensitic transformation, was found on temperature dependences λ(T). Using literature data, concentration dependences of thermal conductivity of the Mg-Li system were plotted in the range X_Li = 0 - 50 at. %. It is shown that an increase in the lithium content in the range of 30 - 50 at. % leads to a further decrease in thermal conductivity.