卷 25, 编号 3 (2018)

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.

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.

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.

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.

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.

The paper considers a heat storage (HS) based on the materials with a “solid-liquid” phase change for a thermal control system for on-board radio electronic equipment (REE) with periodic and short time action. To intensify the heat transfer in the HS design, ribs made of hyper heat-conducting plates are used. The dynamics of temperature fields and phase transformations in the HS volume is studied on the basis of numerical modeling. The results of calculations have shown that the use of ribs in the form of hyper heat-conducting plates allows significantly reducing the amplitude of temperature fluctuations at the seat of the REE unit.