Numerical simulation of the flow with a pseudo-shock in an axisymmetric expanding duct with a frontal inletMazhul, I. I.;Gounko, Yu. P.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010031
Abstract The results of the numerical modeling of a flow with a pseudo-shock in an axisymmetric duct are presented. The duct included a frontal inlet with the initial funnel-shaped compression part and the cylindrical throat part as well as the subsequent expanding diffuser. To create a flow with a pseudo-shock, the duct was throttled with the use of the outlet converging insert. Numerical computations of the axisymmetric flow have been conducted on the basis of the solution of the Reynolds-averaged Navier−Stokes equations and with the use of the k-ω SST turbulence model. As a result of computations, such parameters of the flow were determined as the location of the beginning of the pseudo-shock, the length of its supersonic part, the velocity profiles in different cross sections of the pseudo-shock, the pressure distribution on the duct wall, the total pressure recovery factor, and others. The behavior of these parameters at the freestream Mach number М = 6 was analyzed versus the diffuser opening angle and different degree of the inlet duct throttling.
Experimental investigation of the limits of ethanol combustion in the boundary layer behind an obstacleBoyarshinov, B. F.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010043
Abstract Experimental data on the flow structure and mass transfer near the boundaries of the region existence of the laminar and turbulent boundary layers with combustion are considered. These data include the results of in-vestigation on reacting flow stability at mixed convection, mass transfer during ethanol evaporation “on the floor” and “on the ceiling”, when the flame surface curves to form the large-scale cellular structures. It is shown with the help of the PIV equipment that when Rayleigh–Taylor instability manifests, the mushroom-like structures are formed, where the motion from the flame front to the wall and back alternates. The cellular flame exists in a narrow range of velocities from 0.55 to 0.65 m/s, and mass transfer is three times higher than its level in the standard laminar boundary layer.
Study of the breakup of liquid droplets in the vortex wake behind pylon at high airspeedsArefyev, K. Yu.;Prokhorov, A. N.;Saveliev, A. S.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010055
Abstract The study is devoted to the establishment of regularities in the process of liquid-droplet breakup in the vortex wake behind pylon at high subsonic airspeeds. The article describes the laboratory setup, the diagnostic tools, and the experimental procedure. Structure of the unsteady gas flow behind pylon was examined, and the main characteristics of the generated vortex wake were evaluated. Experimental data concerning the variation of droplet diameters in the gas-dynamic fractionation process versus the flow conditions and liquid injection regimes were obtained. Typical distribu-tions of droplet diameters and velocities in the vortex wake behind pylon are reported. A comparison of experimental data on the rate of the gas-dynamic fractionation process with calculations made using previously developed evaluation procedures was performed. The results of the study may prove useful when choosing the configuration of systems for implementation of liquid injection into a high-speed flow and, also, for validation of mathematical models intended for calculation of parameters of two-phase flows.
Investigation of contact line dynamics under a vapor bubble at boiling on the transparent heaterSurtaev, A. S.;Serdyukov, V. S.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010067
Abstract The paper presents the results of an experimental study of dynamics of vapor bubble growth and departure at pool boiling, obtained with the use of high-speed video recording and IR thermography. The study was carried out at saturated water boiling under the atmospheric pressure in the range of heat fluxes of 30−150 kW/m2. To visualize the process and determine the growth rates of the outer bubble diameter, microlayer region and dry spot area, transpa-rent thin film heater with the thickness of 1 μm deposited on sapphire substrate was used in the experiments, and video recording was performed from the bottom side of the heating surface. To study integral heat transfer as well as local non-stationary thermal characteristics, high-speed infrared thermography with a frequency of up to 1000 FPS was used. High-speed video recording showed that after formation of vapor bubble and microlayer region, dry spot appears in a short time (up to 1 ms) under the vapor bubble. Various stages of contact line boundary propagation were ob-served. It was shown that at the initial stage before the development of small-scale perturbations, the dry spot propaga-tion rate is constant. It was also showed that the bubble departure stage begins after complete evaporation of liquid in the microlayer region.
On injection of hydrate-forming gas into a gas-saturated snowy agglomerate while transition through the ice melting pointShagapov, V. Sh.;Chiglintseva, A. S.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010080
Abstract The paper considers the process of injection of hydrate-forming gas (methane) into a snowy agglomerate (ini-tially saturated with methane). The self-similar problem statement demonstrates that if the warm gas (Te > 0 °C) is injected under a high pressure (pe ≥ p*, where the critical values are found from the initial temperature T0, pressure p0, volumetric snow saturation Si0, and permeability of snow) into the filtration zone with phase transition, this produces four characteristic zones: the nearest zone with all snow transformed into hydrate, therefore, the aggregate filled only with gas and hydrate, the two intermediate zones where gas, snow or water and hydrate are in phase equilibrium state, and the distant zone filled only with gas and snow. The obtained analytical and numerical solutions give an analysis of the influence of key input parameters like initial state of the aggregate, gas injection rate, and its temperature, on the structure and the length of four filtration zones.
Study of evaporating the irradiated graphite in equilibrium low-temperature plasmaBespala, E. V.;Novoselov, I. Yu.;Pavlyuk, A. O.;Kotlyarevskiy, S. G.
2018 Thermophysics and Aeromechanics
doi: 10.1134/S0869864318010109
Abstract The paper describes a problem of accumulation of irradiated graphite due to operation of uranium-graphite nuclear reactors. The main noncarbon contaminants that contribute to the overall activity of graphite elements are iso-topes 137Cs, 60Co, 90Sr, 36Cl, and 3H. A method was developed for processing of irradiated graphite ensuring the volu-metric decontamination of samples. The calculation results are presented for equilibrium composition of plasma-chemical reactions in systems “irradiated graphite−argon” and “irradiated graphite−helium” for a wide range of tem-peratures. The paper describes a developed mathematical model for the process of purification of a porous graphite surface treated by equilibrium low-temperature plasma. The simulation results are presented for the rate of sublimation of radioactive contaminants as a function of plasma temperature and plasma flow velocity when different plasma-forming gases are used. The extraction coefficient for the contaminant 137Cs from the outer side of graphite pores was calculated. The calculations demonstrated the advantages of using a lighter plasma forming gas, i.e., helium.