Home – Home – Jornals – Thermophysics and Aeromechanics 2018 number 6

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 a = 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.

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-dimensional Tollmien-Schlichting wave under similar conditions.

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 supposed reason for stochasticity is the walk of the phase point over a homoclinic structure.

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 mm, 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.

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 significant increase in heat transfer (more than 2.5 times) at mass concentration of droplets M_L1 = 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.

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.

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 condensation 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 oscillations. 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.