Thermophysics and Aeromechanics

Zvegintsev, V. I.;Potapkin, A. V.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030010

Abstract In the present paper, we analyze a suggestion implying the use of the aeroballistic technique for carrying out studies of shock-wave (sonic-boom) characteristics at large distances from the freely flying model. An analysis of the main engineering solutions ensuring the possibility of implementing the proposed experimental facility in the range of flight velocities of examined models from one to two Mach numbers is performed. A list of scientific and engineering problems pertaining to the study of sonic-boom characteristics in the middle and far zones which can be experimentally tackled with the help of the proposed facility is presented.

Cai, J.-C.;Pan, J.;Kryzhanovskyi, A.;E, S.-J.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030022

Abstract The fully 3D turbulent incompressible flow around a cylinder and in its wake at a Reynolds number Re = = 9×104 based on the cylinder diameter and Mach number M = 0.1 is calculated using Large Eddy Simulations (LES). Encouraging results are found in comparison to experimental data for the fluctuating lift and drag forces. The acoustic pressure in far-field is commutated through the surface integral formulation of the Ffowcs Williams and Hawkings (FWH) equation in acoustic analogy. Five different sound sources, the cylinder wall and four permeable surfaces in the flow fields, are employed. The spectra of the sound pressure are generally in quantitative agreement with the measured one though the acoustic sources are pseudo-sound regarding the incompressible flow simulation. The acoustic component at the Strouhal number related to vortex shedding has been predicted accurately. For the broad band sound, the permeable surfaces in the near wake region give qualitative enough accuracy level of predictions, while the cylinder wall surface shows a noticeable under-prediction. The sound radiation of the volumetric sources based on Lighthill tensors at vortex shedding is also studied. Its far-field directivity is of lateral quadrupoles with the weak radiations in the flow and cross-flow directions.

Gounko, Yu. P.;Mazhul, I. I.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030034

Abstract The results of the numerical modeling of the supersonic flow in an axisymmetric duct in which a pseudo-shock arises are presented. The duct includes the frontal inlet with a funnel-shaped part of initial compression of the supersonic flow and with a cylindrical throat part as well as the subsequent (cylindrical or diverging) diffuser where the flow slows down to a subsonic velocity. The flow conditions at the freestream Mach number M = 6 have been considered. Numerical computations of the flow have been done using a Navier–Stokes equations code and the k-ω SST turbulence model. As a result of computations, such flow parameters have been determined as the location of the pseudo-shock beginning, the length of the pseudo-shock supersonic part, the pressure distribution on the duct wall, the total pressure losses as well as the characteristics of flow turbulence. In particular, the variation of the turbulence intensity and turbulent viscosity along the pseudo-shock length have been examined and, based on these characteristics, the possibility of determining the location of a cross section, in which the pseudo-shock can be treated as completed, have been considered.

Zinchenko, V. I.;Gol’din, V. D.;Zverev, V. G.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030046

Abstract The problem of spatial flow around a hypersonic flying vehicle is considered for trajectories with different attack angles for flight through air with chemical equilibrium. The conjugate problem statement gives solutions for gas state in the boundary layer, thermal regime of streamlined body (made of different composites), and the rate of mass loss for heat protecting material. Physical processes in the condensed phase of carbon-containing coatings have complex nature: processes of heating, pyrolysis, heterogeneous oxidation, and sublimation. These processes result in protective material destruction. It was shown that using different materials for passive protection can be beneficial in reduction of the surface temperature, characteristics of thermochemical degradation, and this allows a control over heat and mass transfer for a flying body.

Butt, U.;Egbers, C.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030058

Abstract Measurements of skin friction have been performed on flat and hexagonal concave surfaces using the conventional Clauser-chart method and the Oil film interferometry. The values of shear stress coefficients measured by the conventional Clauser-chart method on a flat plate were found to be up to 13 % higher from the ones deduced by the Oil film interferometry. The velocity profiles required for the Clauser-chart were obtained by using hot wire anemometry. The analysis of the results suggested that the conventional Clauser-chart method cannot be used to predict shear stresses acting on the hexagonal concave surfaces due to the existence of strong pressure gradients. Oil film interferometry not only provides accurate and direct values of shear stress coefficients but also helps to visualize the flow above the surface.

Abdurakipov, S. S.;Dulin, V. M.;Markovich, D. M.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S086986431803006X

Abstract Investigation results on unsteady flow dynamics in a gaseous jet flame with strong swirl, vortex breakdown, and precession of a vortex core obtained by panoramic optical methods are presented, as well as the results of theoretical analysis of the fastest growing modes of hydrodynamic instability. Characteristics of the most unstable self-oscillating mode in the initial region of the turbulent strongly swirling propane-air jet burning in the atmospheric air in the form of a lifted flame are determined. Analysis of data by principal component analysis and linear stability analysis revealed that evolution of the dominant self-oscillating mode corresponds to quasi-solid rotation with constant angular velocity of the spatial coherent structure consisting of a jet spiral vortex core and two spiral secondary vortices.

Jedsadaratanachai, W.;Boonloi, A.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030071

Abstract Numerical investigations on thermo-hydraulic performance and mechanisms of flow and heat transfer in a square channel heat exchanger inserted with right triangular wavy surfaces are examined. The influence of the flow attack angles (30°, 45° and 60°) is investigated for laminar flow (Re = 100–2000). The configurations of the right triangular wavy surfaces are varied as inclined and V-shaped wavy surfaces (the pointing of V-tip with downstream and upstream called “V-downstream” and “V-upstream”, respectively). The insertions of the wavy surfaces in the channel heat exchanger are divided into two types: middle and diagonal insertions. The computational results reveal that the maximum thermal enhancement factor, TEF, is around 2.31 for the 30° V-downstream wavy surface with diagonal insertion at Re = 2000.

Javed, T.;Siddiqui, M. A.;Mehmood, Z.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030083

Abstract This article contains a computational study of free convective flow through a square enclosure filled with liquid gallium saturated porous medium in the presence of a uniform inclined magnetic field. Lower boundary of enclosure is considered to be heated uniformly, upper horizontal boundary is taken insulated, left wall of the cavity is heated linearly, and right wall is heated linearly or taken cold. Navier–Stokes equations governing the flow problem are first exposed to penalty method to eliminate the pressure terms and then Galerkin FEM is employed to solve reduced equations. Grid independent results are achieved and shown in tabular form for numerous ranges of physical flow parameters. To ensure the accuracy of developed code, computed results are compared with those available in earlier studies through figures. It is found that the strength of streamlines circulation is increased due to increase in Darcy number while imposition of vertical magnetic field instead of horizontal magnetic field causes slow rate of increase in strength of streamlines circulation. Whereas, in the case of linearly heated right wall, the average Nusselt number is an increasing function of the Darcy number, and vertical magnetic field causes higher values for average Nusselt number as compared to horizontal magnetic field along bottom and side walls of cavity. Contrarily, in the case of cold right wall, the horizontal magnetic field results in higher values of average Nusselt number as compared to the vertical magnetic field case, and the average Nusselt number reduces as we move along lower and right boundary while increases along left wall with increase in distance.

Sleptsov, S. D.;Rubtsov, N. A.;Savvinova, N. A.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030095

Abstract The problem of radiation-conductive heating and subsequent melting of ice in a climatic chamber in a single-phase approximation of the Stefan problem was posed and solved by mathematical modeling methods taking into account a thin water film formed on the irradiated surface. The fields of temperature and density of the resulting radiation flux are obtained, as well as the rate of melting and heating of the non-irradiated ice surface. Comparison of results with experimental data showed satisfactory agreement.

Syrodoy, S. V.

2018 Thermophysics and Aeromechanics

doi: 10.1134/S0869864318030101

Abstract Simulation results are presented for thermal treatment and ignition of coal-water fuel drops under conditions of radiative-convective heating. The data demonstrate reasonbble compliance between theory and experiment for the integral parameter of ignition process — the delay time of ignition. The radiative component of heat transfer is significant for parameters and conditions of ignition. The increase in the fuel particle size makes this influence bigger. Prognostic potential was evaluated for differnet models of radiative heat tarnsfer. The delay time of ignition obtained from radiative heat transfer model “grey wall” is in good agreement with experimental data. Meanwhile, the method based on radiation diffusion approximation gives the simulation data for delay time much higher than experimental data. It is confirmed that while the process of inflammation of a coal-water particle, the key impotance belongs not to fuel-oxidizer reactions, but rather to a chain of heat treatment events, such as radiative-convective heating, water evaporation, and thermal decomposition of fuel.