Home – Home – Jornals – Thermophysics and Aeromechanics 2025 number 3

The experimental data on mass transfer during ethanol evaporation and combustion in the boundary layer on a horizontal surface are analyzed. The effects of a barrier (up to 15 mm high), external turbulence (up to 26%) and air velocity (up to 58 m/s), close to the flameout velocity in the boundary layer, are considered. The review is supplemented with experimental data for narrowing and expanding channels. The conclusion that the limits of mass transfer intensity during combustion are determined by the regularities for laminar and turbulent boundary layers on a smooth impermeable plate during evaporation without combustion is confirmed.

The paper considers spherical gas bubbles in liquid with radial oscillations induced by acoustic field. The account of development and application of the homobaric model is presented. Several publications on this topic have been discussed.

This work deals with the study of cavitation in a slit channel when flowing around NACA 0012 hydrofoils with smooth and periodic roughness on the surface. The research was aimed at the description of the dynamics of cavitation cavity development on smooth and rough hydrofoils and determination of differences between them. Computer modeling of cavitation flow in a slit channel formed behind an obstacle in the form of a wing was performed in the modern CFD package STAR CCM+. Visualization was obtained, computer modeling was carried out in a wide range of parameters, and a comparison with experimental data on the cavitating flow was made. The effect of periodic roughness on the features of occurrence and development of a cavitation cavity on the hydrofoil is described. The flow structure in roughness cells is shown. The obtained results can be used to control effectively the cavitation process in slit sections of various hydraulic engineering devices.

Results of numerical simulatgions of interaction of a supersonic boundary layer on a flat plate with an oblique shock wave generated by a thin wedge aligned at a right angle to the plate surface are reported. The problem is solved by means of combining a CFD code based on solving the Reynolds-averaged Navier-Stokes equations with the LOTRAN 3.0 software package based on the е^N-method. Specific features of the flow structure with primary and secondary separation regions are identified. It is shown that the shock-induced pressure gradient leads to the develop-ment of Tollmien-Schlichting instability waves and crossflow instability.

The paper describes the response of a viscoelastic layer glued onto a solid base to a non-stationary convective pressure wave. A complete equation of motion of coating material particles in the case of two-dimensional deformations is derived and it takes into account the viscosity of the medium. A system of equations for calculating the longitudinal and transverse dynamic compliance, determined by the ratio of the displacement components to the applied pressure, is obtained. The derived equations allow the description of not only stationary oscillations of the coating, but also the process of their stabilization. It is noted that, in addition to viscosity and Poisson ratio, stationary and dynamic compliances depend only on two parameters: the ratio of the disturbance wave velocity to the propagation velocity of shear oscillations in the coating and the ratio of the wavelength to the coating thickness. An example of calculating stationary compliance for a typical case of a silicone rubber coating is given. Attention is drawn to the need to take into account the transition period of the forced oscillation stabilization, since the coating cannot swing instantly due to inertia and viscosity. Known attempts to calculate this process have been analyzed.

Using a numerical model that includes a system of averaged hydrodynamic equations in the Oberbeck-Boussinesq approximation, differential equations for the Reynolds stress transfer and dissipation rate, a numerical model of the evolution of a flat turbulent spot in a turbulent stratified medium (degenerate background turbulence) is constructed. The components of the mass flux vector and the variance of density fluctuations are found from algebraic presentations of the local equilibrium approximation. Numerical modeling of the evolution of the turbulent mixing zone and the internal waves generated by this zone in a turbulent linearly stratified medium is performed. The calculation results demonstrate a significant effect of background turbulence on the development of the turbulent spot and internal waves generated by the spot. A large-scale turbulent background leads to generation of internal waves of significantly lower amplitude.

The experimental results on the study of the flow structure and pressure distributions on the wall and along the axis of the Coanda ejector mixing chamber are presented. The experiments were carried out in the range of changes in the absolute value of the total pressure in the prechamber P_K = 1.2 - 3.5 atm, which corresponded to both sub- and supercritical jet outflow regimes. The width of the annular gap through which the ejector flow was blown into the mixing chamber took the values h = 0.15, 0.25 and 0.5 mm. An increase in the vacuum on the wall in the initial part of the nozzle was observed with an increase in the total pressure. It was found that the static pressure distributions along the nozzle axis are characterized by the presence of a vacuum region almost along the entire length of the cylindrical channel. At subcritical jet outflows, recirculation zones can form in the vicinity of the channel axis near its inlet. A fundamentally different character of the velocity distribution and pulsation intensity in the cross-section of the mixing chamber is noted, depending on the outflow regimes.

The paper presents the results of parametric numerical modeling of turbulent jet propagation from a slot into a confined space at a Reynolds number of 4×10³. The data of 2D and 3D unsteady Reynolds-averaged Navier-Stokes calculations in the basic confined space configuration close to the experimental conditions of Mataoui et al. (2001) show that the Strouhal number values obtained in the 2D and 3D formulations differ approximately by 10%, but both results are within the uncertainty of the experimental data. The ranges of the open boundary area and the cavity height for which self-oscillation modes are realized are obtained. It is shown that self-oscillations disappear when the transverse size of the open end boundary becomes small and when the cavity height becomes close to its length.

Blocking of a subchannel is one possible scenario for accidents in an operating liquid metal fast breeding reactor. Herein, the understanding the flow behavior neat the locking sites is extremely important. This paper studies the effect of external impact from a sweeping jet on the flow structure in a slot channel behind the fluid lock. We demonstrated that the zone of influence of a sweeping jet on the flow pattern is limited. The spectral analysis method proved that the meandering frequency and frequency of vortex structures propagation in a slot channel corresponds to the Strouhal number equal 0.143. The research results in the case of zero external impact are in compliance with results from other authors.

Experiments were conducted on lqiuid (water) heating by hot vapor in a plate heat exchanger. The coolant agent temperature and flow rates were meausred; the hat balance and heta tarnsfer equastions were applied for calculating the heat flux and heat tarnsferr coefficient asa function of heatwd water flow rate. The mathermatical models are developed for the heat number of tyrtansfer units and for liquid dispalcement in smooth channels. We developed a cellar model for coollant flow pattern while using the surface-type tarnsfer enhancers (wire inserts) and volumetric enhancers (chaotic packing). The calcuations and experimental data are in satisfactory agreement. Experimemntal and simulatiom methods demonstrated that the using of surafec-type enhancers in the problem of high-visocisty lqiuid heating (e.g., industoal oil) increaes the heat transfer coefficient by 2.75 - 6 times amnd the gain in thermal effiecny is about 2.4 - 3.2 times. The gains from using the volumetric-type enhancers are 15 - 20 times and 2 - 3 times, correspondingly, for heating with hot water. The dveloped mathematical model with accounting the flow patterns can be applied in designing or modernization of heat tarnsfer apparatuses in differnet industries.

A problem of controlled time-dependent reduction of wettability of rough metal surfaces obtained after laser ablation by means of periodic laser pulses is theoretically studied. The evolution of the contact angle of wetting of samples having a hierarchical surface structure after laser treatment is determined by their open-air storage, leading to spontaneous adsorption of an organic impurity. The theory of physical adsorption/desorption with a reversible quasi-chemical reaction in accordance with a linear mechanism supplemented with the Gibbs isotherm and the Young equation at the contact point of three phases is considered. The influence of the equilibrium constant and the fraction of the ad-sorbed impurity in ambient air on the rate of system transition to the equilibrium state is analyzed. The method used allows one to model the wettability transition mechanism and to calculate the time evolution of the contact angle of wetting in the case of adsorption of organic substances on the textured surface of the metal.

The simulation principles of slag formation process in the combustion chamber of power plants using high-energy materials such as solid and pasty propellants have been established. This process is determined by the processes of propellant burning, evolution of the multiphase flow inside a combustion chamber and the behavior of slag residues on structural elements. A sequence of using the characteristics of these processes to describe slag formation is shown. A new model for multiphase flow evolution is presented. This model is a key tool for describing the slag formation process. The features of this model are a detailed description of big-fraction solid particles transformation and considering the interaction of condensed and gaseous phases of the flow. The model is based on the combined Euler-Lagrange approach. To validate the model, an experimental study was conducted using a model engine based on aluminized paste propellant. The results of study bring a conclusion about the adequacy of simulation. The directions of further research are determined to solve the problem of simulation the processes under consideration of varying composition parameters and conditions within the combustion chamber.

It is known that passive heat transfer intensification in tubes is carried out by acting on the flow with inserted intensifiers or by changing the shape of the heat exchange surface. The presented work deals with the study of the in-tensification process using spherical turbulators located in a horizontal stainless steel channel. Experimental data were obtained on the heat transfer intensity and pressure drop during circulation of an alcohol-water mixture with a con-centration of 30% by weight at a pressure in the vessel of 0.03 - 0.04 MPa. The efficiency of spherical intensifiers and the pressure drop in the section with spherical intensifiers were compared with the efficiency of spiral intensifiers and the pressure drop in the section with spiral intensifiers at similar operating parameters. It was shown that the efficiency of spherical intensifiers is commensurate with the efficiency of spiral intensifiers at significantly lower pressure drops.

The paper is devoted to non-contact measurements for temperature and emissivity. There are many parameters controlling emissivity: temperature, wavelength, surface condition, etc. There are cases for insufficiently detailed approximation for a body with emissivity depends on the wavelength as an issue of processing the remote measurements of emissivity. A hybrid method aimed to reducing thee multidimensional minimization to one-dimensional case for calculating the emissivity decomposition coefficients is presented. The grey body, linear and quadratic emissivity models are considered. An increasing number of solutions with increasing number coefficients of polynomial decomposition for emissivity is observed. The approach of choosing a proper solution is developed. The limitations on the model parameters numbers are presented: this is related to a growth of relative uncertainties in each parameter and with using the Akaike criterion.

The density of CeAl₂ and NdAl₂ intermetallic compounds in the temperature range of 1550 - 1930 K in the so-lid and liquid states was measured using the method of transmitting samples with a narrow gamma-ray beam with an error of 0.5 - 0.8 %. Approximation dependences for the density of melts of the studied alloys were obtained, and changes in the density during melting and crystallization were determined. The density of melts of a number of other LnAl₂ intermetallics of cerium subgroup of lanthanides was empirically estimated.