Home – Home – Jornals – Thermophysics and Aeromechanics 2013 number 6

We got acquainted with Eduard P. Volchkov in the early sixties, when he moved in Akademgorodok, following his own wish and having made certain of his inner desire to become a scientist.

The flow in the vortex chamber with centrifugal fluidized bed of solid particles was studied experimentally and simulated numerically. The chambers of different configurations were considered, and this allowed us to change the ratio of centrifugal and gravity forces. To estimate the hydraulic losses in the vortex chamber, a simple model was suggested.

Based on the analysis of various aspects of creating a supersonic transport aircraft of the second generation, the necessity of developing unconventional active methods of sonic boom level reduction is demonstrated. Surface cooling is shown to exert a significant effect on formation of the disturbed flow structure up to large distances from the body by an example of a supersonic flow around a body of revolution. A method of reducing the intensity of the intermediate shock wave and excess pressure momentum near the body is proposed. This method allows the length of the reduced (by 50%) sonic boom level to be increased and the bow shock wave intensity in the far zone to be reduced by 12%. A possibility of controlling the process of formation of wave structures, such as hanging pressure shocks arising near the aircraft surface, is demonstrated. The action of the cryogenic mechanism is explained.

The article presents the results of experimental investigation of swirling flow of lean propane/air flame in a model combustion chamber at atmospheric pressure. To study the unsteady turbulent flow, the particle image velocimetry technique was used. It was concluded that dynamics of high swirl flows with and without combustion was determined by a global helical mode, complying with a precessing double-spiral coherent vortex structure. The studied low swirl flame had similar size and stability characteristics, but amplitude of the coherent helical structure substantially oscillated in time. The oscillations were associated with intermittently appearing central recirculation zone that was absent in the non-reacting flow. It is expected that the low swirl flow without the permanent central recirculation zone should be more sensitive to an external active control. In particular, this result may be useful for suppression of thermoacoustic resonance in combustion chambers.

The peculiarities of the heat and mass exchange in a laminar boundary layer with combustion at the injection of the fuel mixture H2/N2 through the permeable surface are considered. It is shown that at a certain value of the injection parameter, the value of the heat flux into the wall averaged over the length has a maximum. An analytic estimate is proposed for determining the maximum heat flux at the combustion depending on the injection intensity. The obtained relations agree with the results of experimental studies and numerical modelling.

Experiments with ethanol combustion on horizontal surfaces revealed the most general properties of a boundary layer with chemical and phase transformations. The list of flow features includes development of large-scale structures and manifestation of volumetric forces, which impact the flow stability and heat and mass transfer. It was demonstrated that the range of velocities ensuring flame existence is wider for flow past a rib than for flow past a backward-facing step. The nature of mass transfer in a reactive flow past an obstacle is transient and remains of that kind until the flame blow-off. For a flow above a horizontal wall at Reynolds numbers Re < 5⋅10⁴, the intensity of mass transfer is twice higher than for combustion below the wall. When the combustion occurs below the wall, the surface temperature gradients are higher.

In the present paper, we report results of an experimental study of the influence which a vortex-generating element installed upstream of the main obstacle has on the separated flow and heat transfer in a cross-flow cavity-trench. The element was a small cross-flow rib whose height was an order of magnitude smaller than the depth of the cavity. In the experiments, the variable parameters were the angle of inclination of the frontal and rear walls of the cavity, the rib height, and the rib-to-cavity distance. It is shown that the introduction of additional vortical perturbations into the recirculation zone leads to a substantial modification of both the vortex production process and the distributions of pressure and heat-transfer coefficients. Optimal height of the mini-turbulizer and its optimal location are defined by the fall of the re-attachment point of mini-rib-generated flow onto the rear wall of cavi-ty. In the latter situation, the maximal value of the heat-transfer coefficient increases as compared to the case with no vortex generator used, the increase amounting to 30 %.

Results of an experimental study of a flat plate film cooling efficiency from a single row of inclined holes embedded in a "shallow" trench are presented. It is shown the cooling efficiency of such a configuration is much greater than that of the traditional configuration of inclined round holes. This provides more uniform surface coverage by the coolant film. The flow external turbulence increases the film cooling efficiency by 5–8%, while the freestream flow acceleration reduces it by 10–15%.

Experimental results on the effect of the methods of gas cooling arrangement on thermal efficiency are presented. The swirl cooling is considered at both injecting along the axis and co-axial supply of the cooling gas. The influence of swirling degree, density ratio of both flows and flow regimes on the efficiency of near-wall cooling is considered.

The model, experimental equipment, and test program are briefly described. A method of determining the aero-dynamic characteristics of the model on the facility with free oscillations is presented. Aerodynamic derivatives of the pitching moment of the model are obtained for two positions of the axis of rotation and Mach numbers M_∞ = 2, 4, and 6. At M_∞ = 2, the model with the rear position of the axis of rotation is not balanced at low angles of attack, whereas irregular self-sustained oscillations of the model with the frontal position of the axis of rotation arise.

The cycle of experiments on interaction between the co-current gas flow and the near-wall liquid film were carried out at high gas flow velocities, including the supersonic ones. The local parameters of the near-wall film were measured by the capacitance probes. It is shown that the co-current gas flow affects the near-wall film significantly, causing intensive wave formation, droplet detachment from the film surface, and their entrainment by the gas flow. It is determined that a relative amount of liquid entrained by the co-current flow is generalized by the Weber number of this gas flow.

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

The method of energy separation in a high-speed flow proposed by A.I. Leontyev is investigated numerically. The adiabatic compressible gas flow (of a helium-xenon mixture) with a low Prandtl number in a planar narrow duct and a flow with heat exchange in a duct partitioned by a heat-conducting wall are analysed. The temperature recovery factor on the adiabatic wall, degree of cooling the low-speed flow part, temperature efficiency, and the adiabatic efficiency in a duct with heat exchange are estimated. The data are obtained for the first time, which make it possible to compare the efficiency of energy separation in a high-speed flow with the efficiency of similar processes in vortex tubes and other setups of gas-dynamic energy separation.

The effect of the expansion of hollow micro-spherical droplets due to their heating at their motion in a plasma jet is considered by the example of ZrO₂. A fairly simple model is proposed, which accounts for the variation of the droplets size and shell thickness because of the thermal expansion of the gas cavity as well as their possible evaporation. The conducted computations have enabled the assessment of the scale of the variation of diameter (10-20 %) and shell thickness (up to 50 %) of ZrO₂ particles under the conditions typical of the plasma treatment of powder materials and producing the coatings. The influence of the given effect on the dynamics of particles heating and acceleration is investigated, and a comparative analysis of the behavior of hollow and dense particles in plasma jet is done.