Home – Home – Jornals – Thermophysics and Aeromechanics 2024 number 1

In a model experiment, the process of interaction of an external artificial disturbance with the leading edge of a straight wing model was investigated. The characteristics and features of the development of boundary layer disturbances, generated as a result of the interaction of external disturbances, and the blunted leading edge of the wing model have been obtained. The research was carried out in a subsonic low-turbulence wind tunnel using a hot-wire anemometry method for detecting disturbances. Localized disturbances generated in the incoming flow were shown to induce longitudinal streaky structures in the boundary layer of the straight wing. High-frequency wave packets (precursors) appeared at the boundaries (fronts) of longitudinal structures. The dynamics of the development of wave packets and localized longitudinal structures in the boundary layer above the wing profile in a gradient flow was studied.

The results of experimental measurements are presented to assess the correlation characteristics of disturbances in the boundary layer of a flat plate with a sharp leading edge and pulsations of the incoming flow in cases of natural pulsations and influence of an N-wave for Mach 2 on the leading edge. The parameters of the cross-correlation of signals from two constant-temperature anemometry (CTA) are obtained digitally. The frequency ranges with apparent correlation between the mass flow rate pulsations measured by the probes are determined.

The gas temperature measurements at the level of the inner wall of Ranque vortex tubes of the square and circular cross sections with variations in the cold mass fractions for both tubes showed the presence of three characteristic zones of temperature growth, which do not change over a wide range of the cold mass fraction. These zones are typical when analyzing the flow in a vortex tube within the framework of the flow crisis concept.

The flow in the vicinity of the source of controlled harmonic non-stationary perturbations of a gas medium, applicable for generating Görtler vortices in a compressible boundary layer, is studied. The source has a flat surface with linearly arranged cylindrical channels, leading alternately to two cavities of variable volume. Various configurations of the source are considered: with separate channel outlet openings and with a slit opening above them. Numerical simulation is performed in the Solid Works Flow Simulation package, and experimental measurement of gas velocity is realized by the PIV method. The developed source is shown to create periodic velocity fluctuations with an amplitude of up to 2 m/s at a frequency of 1 kHz near the surface. The shapes of the profiles of velocity normal to the surface along the source are close to sinusoidal in both time and space.

A method of panoramic temperature measurement based on registering the fluorescence of thin-walled coatings on the inner surface of a flying vehicle model is considered. The method allows investigations in optically polluted flows of high-enthalpy short-duration wind tunnels. The temperature and heat fluxes on the aerodynamic model surface are retrieved by means of combining the results of temperature measurements with the numerical solution of an adjoint problem of the flow around the flying vehicle. Implementation of this method in practice is performed in the flow of a hotshot wind tunnel based at ITAM SB RAS.

Investigation results on the air flow in a convergent channel with a hot bottom wall at a set constant heat flux or a set constant wall temperature are presented. The numerical simulation was carried out in the OpenFOAM software using the k-ω- SST turbulence model. The verification of simulation results demonstrated a good agreement between the calculated data and the experimental velocity profiles and the thermal Stanton number. The study showed that an increase in the temperature of the convergent channel wall leads to the phenomenon of the streamwise velocity overshoot, suppression of turbulence and a decrease in the skin-friction coefficient and thermal Stanton number. In contrast to a zero pressure gradient flow, the type of thermal boundary conditions has a noticeable effect on the skin-friction and heat transfer in the convergent channel.

Numerical simulations of an underexpanded supersonic jet exhausting from a circular nozzle are reported. The study is performed in a three-dimensional formulation using two different approaches: Navier-Stokes equations and Direct Simulation Monte Carlo method. In both cases, a reverse flow zone is formed behind the Mach disk in the first shock cell. Thus, this phenomenon, which was previously observed in axisymmetric simulations, cannot be attributed to inaccuracies of approximation of these equations near the axis of symmetry.

Influence of streamwise slots with the orientation angle φ = 0 and various depths h (corresponding Reynolds number Re_h = 0 -2000) on the stability of the supersonic (M = 2) flat-plate boundary layer with relation to natural disturbances of the first (vorticity) instability mode driving laminar-turbulent transition was investigated experimentally. Experiments shown that such kind of disturbances can be stabilized by small-depth streamwise slots, wherein the maximum stabilization occurs at the Reynolds number (based on the slot depth) of about Re_h ≈ 1000.

The work is devoted to the study of random statistical processes in two-phase flows. The objective is to obtain new computational and experimental data on the influence of previously undetermined factors on the trajectories of particle motion, their segregation, and the formation of a locally continuous flow field of the dispersed phase in supersonic turbulent two-phase flows. The results of computational and experimental study of the flow features of a two-phase supersonic flow are presented. A new experimental method was applied for analysis of influence of random statistical factors on the particle distribution in a high-speed carrier flow. The physical basis of the proposed method is to indicate the flow rate of the dispersed phase by means of particle adhesion to an obstacle installed in the flow. In order to analyze the segregation of the dispersed phase in the flow, the approach of quasi-continuumization of individual particle trajectories is applied. The method obtains a locally continuous flow stress field for dispersed phase flow. Empirical coefficients resulting from the influence of random statistical factors on the motion of dispersed particles in a two-phase flow are determined. The obtained computational and experimental data clarify the prediction of the distribution and segregation of dispersed phase particles with a size of 15÷40 microns in a supersonic free flow.

Results of a numerical study of supersonic flows formed in channels with a square cross section are reported. Configurations consisting of a constricting entrance section formed by four compression wedges aligned at a right angle to each other and a subsequent channel with a constant cross section are considered. The initial shock waves formed on the nose compression wedges pairwise intersect each other in dihedral corners of the configuration along the swept lines, and a complex system of reflected and subsequent interacting shock waves of the general three-dimensional position is formed further downstream. The data are obtained in a supersonic range of freestream Mach numbers М = 2 - 4 for compression wedge angles of 3° and 8° in flows with both regular and irregular interaction of the initial shock waves in dihedral corners of the configuration.

Measurements of full pressure pulsations in the mixing layer of a supersonic, strongly underexposed jet were performed. The resulting pressure was converted into a longitudinal velocity, which allowed determining the main characteristics of the layer: its growth rate and thickness, longitudinal and transverse dimensions of disturbances, intensity, and spectral composition of turbulence. The layer under consideration was in a state of saturation, with a wide range of disturbances being realized within. The measured growth rate of the layer turned out to be four times higher than that calculated by a statistically generalized method. The intensity of disturbances of the longitudinal velocity component was determined in the considered layer by two groups of disturbances - low-frequency and high-frequency - with approximately equal inputs. From the analysis of the measurement results, it follows that the mass transfer across the layer is inversely proportional to the lengths of the vortices, and in the upper part of the frequency range of intense disturbances it is many times higher. This indicates that intensive mixing generates rapid growth rate of the layer.

It is shown that the vibration transfer and working medium pressure pulsations through vibration-isolating pipeline junctions of various plants may increase by two or three orders of magnitude with an increase in the vibration frequency and in the presence of incompressible working fluid. The results of research of the found physical models that determine this phenomenon are presented. The experimental results for a spatial three-component broadband active vibration-protection system (AVS) for vibration damping beyond the vibration isolation junction with liquid are considered. An experimental plant scheme for studying the simultaneous spatial active damping of dynamic forces, vibrations and pressure pulsations downstream from the junction has been given. Calculated dependences of the maximum efficiency of considered AVS on frequency are obtained. Efficient active damping of forces is shown to be attainable in an open loop without feedback. While damping in an open loop at the experimental plant, the efficiency of active damping of dynamic forces is obtained in three directions up to 10 dB or more in the frequency range from 5 to 800 Hz (more than seven octaves). The analysis of scientific publications reveals the uniqueness of this result. In this case, there are no zones of negative efficiency outside the active damping frequency range, which appear while using other methods of active damping.

An experimental method is proposed for determining the frequency response of a hot-wire and hot-film system using short-pulse laser action on a sensor. The possibility to obtain frequency response by this method is demonstrated. The frequency response is obtained from constant temperature anemometers of two manufacturers with two types of sensors: surface thin-film and wire.

The experimental results on heat transfer when a pulsed multi-nozzle spray flows onto a vertical surface are presented. The behavior of the effective heat transfer coefficient averaged over time and over the entire heat transfer surface has been studied. The experiments were carried out in the regime of evaporative cooling at a constant temperature of the heat transfer surface T_w = 70°C. The duration of pulses for supplying the liquid phase of the spray τ and their repetition frequency F were varied in the experiments within wide limits: τ = 1 ÷10 мс and F = 0,25 ÷ 50 Hz. In addition, the effect of droplet phase flow rate on heat transfer was studied by changing the pressure in front of the nozzles (ΔP_L = 0,05 ÷ 0,6 MPa). Preliminary studies have shown that heat transfer during spray impingement onto a surface can be strongly influenced by the co-supply of air due to turbulization of the wall layer and the return of droplets reflected from the surface. It has been established that the main factor determining the intensity of heat transfer when the spray flows onto the surface is the time-averaged mass velocity of the liquid phase. Using this value, generalization of experimental data on the heat transfer coefficient and the thermal efficiency parameter of a pulsed spray was achieved.

The paper demonstrates a possibility of applying the known class of analytical self-similar solutions in the form of the traveling heat wave for a system of nonlinear integro-differential equations describing radiative transfer for non-stationary, quasi-stationary and regular modes of solution behavior. The solutions are constructed for a kinetic model in the Cartesian geometry under the assumption of local thermodynamic equilibrium with specially chosen absorption and scattering coefficients. A test problem for different solution modes is provided.

In this review paper, using the example of AM-Pb and AM-Bi melts (AM is an alkali metal), modern ideas on the nature of chemical short-range order in liquid metal systems with partial ionic bonding are briefly presented. Generalization and analysis of the experimental data obtained by the authors on the volumetric properties and mutual diffusion in liquid alloys of alkali metals with lead and bismuth have been carried out. The behavior of these properties is shown to generally agree with existing simple models that assume the presence of ionic complexes in melts, which are gradually dissociated with increasing temperature. At the same time, the need to refine the structure of polyanionic complexes in liquid AM-Bi systems is confirmed.

The paper describes an experimental study of the influence of multiple cyclic pressure loading on the service life and sorption performance of a composite sorbent whose granules consist of selectively permeable (to helium) microspheres as a filler and pseudoboehmite as a porous binder. A test bench is specially designed and fabricated for the study, which makes it possible to model various operation regimes of gas-separation plants in the pressure range up to 10 MPa. Cyclic tests of pressure loading of the granulated composite sorbent are performed, and the sorption capacity of the sorbent with respect to helium is measured. It is found that the composite sorbent retains its integrity and sorption performance under cyclic loading of 1000 cycles and more at pressures up to 10 MPa.

The paper presents the experimental results on the disposal of infected medical waste using low-temperature plasma. It is shown that infected medical waste can be processed using plasma technology. During plasma destruction of these materials, their biological disinfection with production of chemically inert, safe slag is guaranteed.

The paper is concerned with an experimental study of heat transfer and boiling crisis development on a biphilic silicon surface made using a set of methods, including chemical vapor deposition and laser texturing. It is shown that the use of a biphilic surface with the proposed configuration of hydrophobic zones on a superhydrophilic base leads simultaneously to an increase in heat transfer by 60% and an increase in the critical heat flux by 76% as compared to an unmodified surface.