Thermophysics and Aeromechanics

Morozov, S. O.;Lukashevich, S. V.;Soudakov, V. G.;Shiplyuk, A. N.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S086986431806001X

Abstract The present work was devoted to an experimental study of small angles of attack and cone nose bluntness on the efficiency of stabilization of high-frequency disturbances in hypersonic boundary layer with a passive porous coating. The experiments were carried out on a cone with an apex half-angle 7° and nose bluntness radii R = 0.03, 0.5 and 1 mm installed under angles of attack α = 0–1° at the freestream Mach number M∞ = 5.8. High-frequency pressure fluctuations on the sides of the cone with the solid and porous surfaces were measured. It is shown that at all angles of attack and cone bluntness, the passive porous coating permits an efficient suppression of disturbances in hypersonic boundary layer both on the windward and leeward sides of the cone.

Katasonov, M. M.;Pavlenko, A. M.;Kozlov, V. V.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060021

Abstract The hot-wire anemometry technique is used to study the development of controlled disturbances in a straight wing boundary layer. Three-dimensional surface oscillations with large amplitude generate two types of disturbances: the localized longitudinal structures and wave packets. In downstream direction, the intensity of localized longitudinal structures decreases. The wave packets manifest themselves near the fronts of longitudinal localized structure in the flow region with adverse pressure gradient. In the separation flow area, an intensive growth of the wave packets amplitude is observed. The spatial development of the wave packets coincides with the development of three-dimen-sional Tollmien–Schlichting wave under similar conditions.

Geshev, P. I.;Chernykh, A. I.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060033

Abstract The Hamiltonian equations of the motion of a system of N ideal point vortices in a simply connected two-dimensional region have been obtained by the methods of the theory of functions of a complex variable. It is shown that the motion of two vortices in a circle is integrated exactly; the periods of this motion have been determined. The motion of two vortices in a region bounded by a lemniscate has been investigated by the method of secant planes in the phase space. The stochastic trajectories have been revealed here, which have continuous power spectra. The sup-posed reason for stochasticity is the walk of the phase point over a homoclinic structure.

Zinovyev, V. N.;Kazanin, I. V.;Lebiga, V. A.;Pak, A. Yu.;Tsibulsky, N. G.;Vereshchagin, A. S.;Fomin, V. M.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060045

Abstract The paper is devoted to the study of the permeability of hollow microspherical membranes to helium with a narrow fraction of MS-V-1L microspheres taken as an example. In the course of the study, a special experimental facility for obtaining the sorption curves of various gases at given pressures and temperatures was created. A procedure for carrying out experiments and processing experimental data with the aim of evaluating the coefficient of helium permeability for the investigated type of hollow membranes was approbated. For the selected narrow fraction of MS-V-1L microspheres with diameters in the range from 35 to 50 μm, the helium permeability coefficient of the particle-wall material in the temperature range from 20 to 110 °C and the activation energy of the helium sorption process by the microspheres were determined.

Pakhomov, M. A.;Terekhov, V. I.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060057

Abstract The effect of flow swirl parameter and thermophysical properties of the droplet of water, ethanol, and acetone on the structure of turbulent flow and heat transfer in a gas-droplet flow was studied numerically. To describe the dynamics and heat and mass transfer of the two-phase flow, the Eulerian approach was used. The growth of the volume fraction of small particles on the tube axis is typical of a swirling flow because of their accumulation in the zone of reverse flows due to the turbophoresis force. It is shown that the addition of droplets leads to a signifi-cant increase in heat transfer (more than 2.5 times) at mass concentration of droplets ML1 = 0.1 in comparison with a single-phase swirling flow. Intensification of heat transfer with the use of ethanol droplets is higher than that for water droplets (approximately 10–20 %) and acetone (up to 65 %). When using the droplets of ethanol and acetone, the region of two-phase flow existence reduces, and the degree of suppression of carrier phase turbulence decreases. This is due to a more rapid evaporation of droplets of volatile liquids.

Kulikov, Y. M.;Son, E. E.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060069

Abstract This paper deals with 3D flow of thermoviscous fluid in the low compressibility approximation within a cubic-shaped domain enclosed between two flat plates with different temperatures. For two other directions, the problem statement assigns periodic boundary conditions, while the steady pressure drop is sustained for the head flow direction. Such formulation allows to trace the evolution of initial disturbances imposed on the main flow depending on perturba-tion properties. In this case, we consider a degenerate one-dimensional divergence-free noise that is modified by a special correlation filter. When the divergent noise is generated, the solenoid nature of random velocity field must be restored. The simulation demonstrates that random disturbance field development leads to two different scenarios: for the first low-amplitude case, the velocity profile loses initial inflection point and its flowrate increases by 1.5–1.6 times, but for the second one, the flow turbulization occurs destroying the flow core and decreasing the flowrate. In both outcomes, the transition to a steady flow mode in terms of either stationary velocity fields or statistical averag-es takes place for a long interval: up to t~200 dimensionless time units. The analysis of simulated flow is based on integral kinetic energy curves and enstrophy and also via spatial averaging of the obtained data arrays.

Kabova, Yu. O.;Kuznetsov, V. V.;Kabov, O. A.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060070

Abstract The joint steady-state motion of a rivulet of incompressible liquid and a gas flow in a microchannel was studied taking into account the action of gravity forces, tangential stress at the gas-liquid interface, and Van der Waals forces. The values of contact angle are calculated for various values of liquid and gas flow rates. It is shown that for a constant liquid flow rate, an increase in gas velocity leads to a decrease in the height of rivulet, and the surface of rivulet becomes flatter. A significant deforming effect of rivulet on the velocity distribution in gas is found.

Aktershev, S. P.;Levin, A. A.;Mesentsev, I. V.;Mesentseva, N. N.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060082

Abstract The results of an experimental and theoretical investigation of highly subcooled ethanol in an annular flow-passage duct under the conditions of pulsed heat generation in the wall cooled by liquid flow are presented. The formation of a vapor film on the heater wall and long-lasting pressure oscillations of high amplitude in the duct (the self-oscillatory regime) have been observed in experiments. A mathematical model of the ethanol boiling up has been developed to take into account the evaporation of the overheated liquid near the heater wall and the vapor condensa-tion in the flow of a subcooled liquid. The proposed model describes both the decaying oscillations of the vapor layer and the development of the self-oscillatory regime, which predicts well the amplitude and frequency of nonlinear oscil-lations. Numerical computations have shown that the self-oscillatory regime is realized due to evaporation of a periodically renewed microlayer on the heater wall. Computational results agree well with experimental data.

Salikhov, T. Kh.;Khodjaev, Yu. P.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060094

Abstract Based on the system of nonlinear equations of thermal conductivity for stationary temperatures of the gas layer, substrate, the first and the second layers of samples with a volumetric optical absorption coefficient, the features of the formation of a stationary temperature field in the photoacoustic cell have been investigated. Analytical expressions for the temperature field of the gas layer, two layers of the sample and the substrate, as well as a system of interrelated nonlinear algebraic equations for the steady-state temperature of the irradiated and rear surfaces of the first layer and the boundary between the second layer β and the substrate have been obtained. The numerical solution of the system of nonlinear algebraic equations shows that with the increase of the absorption coefficient of the corresponding layer and the gradual transition from the condition βili <1 ( li is the layer thickness) to the condition βili ≥1, heating increases significantly, and the dependences of the characteristic temperatures on the intensity of the incident beam I0 become nonlinear. It is shown that the sign of the thermal coefficient of the temperature dependence of emissivity significantly affects the dependences of the temperature increment of the surfaces of all layers on the intensity of the incident beam.

Sergachev, D. V.;Kovalev, O. B.;Grachev, G. N.;Smirnov, A. L.;Pinaev, P. A.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318060100

Abstract The problem of measurement of the in-flight velocity and temperature of particles in the light field of a pulsedperiodic laser was solved using contactless detection methods. The solution of the problem is based on using a spectrometer and a complex of laser and optical means. The diagnostic technique combines two independent methods for measuring the in-flight particle velocity: a passive one, based on the registration of the natural radiation emitted by the heated particles in the gas flow, and an active one, using the effect due to laser-beam scattering. Histograms of the statistical distributions of particle velocities for two operating modes of a coaxial nozzle were presented. There is no laser radiation in the first mode. There is pulsed laser radiation in the second mode. In the experiments, various powders (Al2O3, Mo, Ni, Al) with particle size distributions typical of laser deposition technology and various working gases (air, nitrogen, argon) were used. СО2-laser works in pulse-periodic mode with a mean power up to 2 kW. Pulsed power reaches several ten/hundred kilowatts. It is shown that in the field of laser radiation, powder particles acquire additional acceleration due to the evaporation and the appearance of a reactive force due to the recoil pressure of the vapors emitted from the irradiated part of the particle surface. It is shown that laser radiation can significantly affect the velocity and temperature of powder particles being transported by a gas jet. At the maximum carrier-gas velocity of up to 30 m/s, the velocities of single particles due to the laser-induced acceleration can reach the values of the order of 120 m/s.