Investigation of the influence of a local change in surface temperature on the laminar boundary layer stability in a hypersonic nozzleMorozov, S. O.; Shiplyuk, A. N.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320050017
The influence of a local change in surface temperature of a contoured nozzle corresponding to the Mach number M = 6 on the boundary layer stability and laminar-turbulent transition is numerically studied. The profiles of the laminar boundary layer are obtained by solving the Navier-Stokes equations with the use of the Ansys Fluid software system. N-factors of the growth rates of the Goertler vortices and also disturbances of the first and second Mack modes are calculated in the approximation of the linear stability theory. It is demonstrated that local heating ensures lower growth rates of the amplitudes of the Goertler vortices and the first Mack mode as compared to the base case; the more intense the heating, the more expressed this effect. The growth rate of the amplitude of the second-mode disturbances decreases during local heating of the nozzle to a temperature close to the stagnation temperature and increases at higher temperatures of local heating. It is found that local cooling leads to an increase in the growth rates of the amplitudes of the Goertler vortices and second Mack mode. The amplitude of the first Mack mode in the cooling region is smaller than that in the base case; however, further downstream, it is much greater than that in the base case. It is found that the surface of contoured nozzles should be heated in the region of the maximum growth rates of the amplitudes of the Goertler vortices; the higher the temperature, the more pronounced the expected effect. However, the maximum possible temperature is determined by the growth of the second Mack mode. The optimal option is to use the temperature of local heating of the surface at which the growth rate of the amplitude of the second mode is smaller than that of the Goertler vortices.
Mode decomposition of disturbances in a supersonic flowTsyryulnikov, I. S.; Gromyko, Yu. V.; Poplavskaya, T. V.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320050029
Controlled disturbances are inserted into the wind tunnel flow, and probing measurements of the fields of the amplitudes of pressure and phase velocity oscillations of these disturbances are performed. Based on the relations for inviscid interaction of long-wave vortex, entropy, and acoustic disturbances with the shock wave on a wedge and numerical simulations, the coefficients of conversion of various modes to pressure oscillations on the model surface are determined for the test conditions of a supersonic flow in the T-327B blowdown wind tunnel located at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences. The method of mode decomposition for controlled disturbances with the use of disturbance conversion coefficients is implemented in the case of a flat plate model with a sharp leading edge aligned at different angles of attack and side-slip in the flow.
Numerical study of a round jet impinging on an axisymmetric grooved surface: effect of the groove sizeDerdouri, A.; Nemouchi, Z.; Benhacine, A.; Abed-Meraim, K.; Sakout, A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320050042
The effects of the groove size on the dynamical and thermal behavior in a round jet impinging on an axisymmetric corrugated surface are investigated numerically. The geometry is similar to that considered in the experimental study Sagot et al. (2010, Inter J. Therm. Sci., 49, 1026–1030). Three side lengths of the square groove cross section are tested, 1/8, 1/4, and 3/8 of the jet diameter. A comparison is made with the flat plate case. The nozzle-to-plate distance is H = 2D, the Reynolds number is Re = 23000, and the ratio of the plate-radius to nozzle-diameter is R/D = 6. The SST k-ω model is employed to take account of turbulence effects. An attempt is made to understand thoroughly how key parameters such as mean velocity, turbulent kinetic energy, and temperature fields can influence the heat transfer performance. The local normal-to-wall temperature gradient and, thus, the local heat flux through the fluid/wall interface are strongly dependent on these parameters. This justifies our interest in analyzing the distributions of such determining factors in the wall jet and, particularly, in the recirculating zones inside the cavities. Their imprints on the friction coefficient and the local and averaged values of the Nusselt number are highlighted.
Numerical study of thermal wall protection from a hot air by the evaporation of a binary liquid filmBouchelkia, I.; Feddaoui, M.; Benkahla, Y. Kh.; Charef, A.; Labsi, N.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320050066
In this paper, a numerical study is performed to investigate the influence of adding glycol or alcohol to water on the thermal protection of a channel wall from hot air by evaporating this binary liquid film. The coupled governing equations in both phases with the boundary and interfacial conditions are solved using a finite difference numerical scheme. The effectiveness of adding a fraction of glycol or ethanol to water for the thermal wall protection is analysed. The influence of the film composition, the liquid mass flow, the velocity and the gas flow temperature at the inlet, on the intensity of heat and mass transfer is discussed. The results indicate that with a lower inlet liquid flow, the mixture ethanol-water presents the best solution for the thermal wall protection compared to ethylene glycol-water mixture. However, for higher inlet liquid flow rate, the two mixtures have the same trends for a water amount higher than 60%. The presence of ethylene glycol in the mixture reduces the heat transfer by latent mode. Consequently, the decrease of the wall temperature is mainly due to the sensible heat flux. The ethylene glycol-water mixture offers the best wall protection from the hot air stream. Accordingly, the most important factor for the wall protection is the thickness of the film that acts as an insulator. The pure water presents a better thermal protection but a very bad conservation of the liquid film. Furthermore, the heat transfer by sensible heat exchange contributes efficiently in wall protection than heat transfer by latent mode.
Studying coolant hydrodynamics in the area of a guide channel of fuel assembly with intensifier gridsDmitriev, S. M.; Dobrov, A. A.; Doronkov, D. V.; Doronkova, D. S.; Pronin, A. N.; Rubtsova, E. V.; Ryazanov, A. V.; Solntsev, D. N.; Khrobostov, A. E.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S086986432005008X
The article presents the results of studies of the coolant flow in fuel assemblies behind the intensifier grids of FA-Square reactors of the PWR type. The aim of this work is to evaluate the effectiveness of using various designs of the intensifier grid for the flow mixing. To achieve this goal, a number of experimental studies are carried out on an aerodynamic stand with scale models of fragments of fuel assemblies with intensifier grids of various designs. Adjacent cells of the guide channel, the design feature of which is the different spatial orientation of turbulators installed on the intensifier grids, are selected as a representative area of research. The general flow pattern is represented by vector fields of tangential velocities, as well as by graphical dependences of the distribution of transverse velocities in the gaps between the rods of the research area. To evaluate the efficiency of using various intensifier grids’ designs for the coolant flow mixing, the parameters of intracellular vortex formation and intercellular mixing are analyzed. Analysis of the spatial distribution of tangential flow velocities allows studying and detailing the coolant flow pattern behind the mixing grids with various designs of deflectors. The accumulated database on the coolant flow in the FAKVADRAT is the basis for engineering justification of the PWR reactor core designs. The results of experimental studies are used to verify CFD codes of both foreign and domestic development, as well as the programs for detailed cell-based calculation of active zones in order to reduce conservatism in justifying thermal reliability.
Improving adiabatic film-cooling effectiveness spanwise and lateral directions by combining BDSR and anti-vortex designsGrine, M.; Boualem, Kh.; Dellil, A. Z.; Azzi, A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320050091
In the present study, a numerical investigation was conducted to enhance the film cooling efficiency by using anti-vortex designs. Four configurations are considered in this paper, which are the configuration with the streamwise cylindrical injection, the case with an upstream Barchan dune shape ramp (BDSR), the case with sister holes and the configuration that combine the Barchan dune shape with sister holes. The effects of a blowing ration (M = 0.5, 0.85, 1.0 and 1.5) on the film cooling effectiveness are considered. The validation shows good agreement and almost all flow structures are well reproduced by the RANS computation. Results show that the Barchan dune shapes with sister holes have an influence on thermal and flow structures, this configuration substantially augments the film cooling efficiency.