Thermophysics and Aeromechanics

Boiko, A. V.;Ivanov, A. V.;Kachanov, Yu. S.;Mischenko, D. A.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040013

Abstract We have examined, both experimentally (using fully controlled disturbances) and theoretically, the weakly-nonlinear development stages of unsteady (in general) Görtler instability of a boundary layer over a concave surface. Primary attention was given to early manifestations of nonlinearity in the development of unsteady Görtler vortices belonging to the first, most rapidly growing, mode in the discrete spectrum of the stability problem. We have investigated the manifestations of instability versus the frequency of the fundamental (primary) Görtler mode and the initial disturbance amplitude. The weakly-nonlinear stage of development of unsteady Görtler vortices was found to display the following characteristic features: (a) nonlinear interaction among the combination modes in the frequency-wavenumber spectrum, (b) distortion of the wall-normal profiles of disturbance amplitudes and phases, (c) reduction of the growth rate of the fundamental Görtler mode and the majority of combination modes, and (d) a decrease in the phase velocities of unsteady disturbances. It was found that the disturbances enter the region of weakly-nonlinear development after the amplitude of the fundamental frequency-wavenumber mode reaches a threshold of 4–6 %, this value being much greater than that for Tollmien — Schlichting waves (1–2 %) but significantly lower than that for the cross-flow instability modes in three-dimensional boundary layer (more than 10 %).

Petrov, G. V.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040025

Abstract The nonlocal equations for two harmonics of the Tollmien — Schlichting wave and averaged parameters of the incompressible boundary layer on a plate are derived. Computed results show that the wave gives rise to a friction increase on the wall, and this increase becomes substantial when the ratio of the amplitudes of the second and main harmonics reaches 0.5.

Terekhov, V. I.;Gnyrya, A. I.;Korobkov, S. V.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040037

Abstract Experimental results on convective heat transfer from a single cube on a flat surface are presented for different attack angles to the incident flow and Reynolds numbers. The character of vortex formation and the effect of flow structure on heat transfer at detached flow around a cube were studied by visualization. Local heat transfer and heat transfer averaged over the separate faces and the whole lateral surface of the cube were studied. Contribution of separate cube faces to total heat transfer depending on the attack angle was estimated. Data obtained were compared with those published in literature. The reasons for observed differences caused by the effect of many factors: boundary layer thickness, turbulence level of the incident flow, channel constraint, etc., are analysed.

Zebbiche, T.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040049

Abstract When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant any more and start to vary with this temperature. The gas remains perfect; its state equation remains always valid, except, it is named in more by calorically imperfect gas. The aim of this work is to trace the profiles of the supersonic axisymmetric Minimum Length Nozzle to have a uniform and parallel flow at the exit section, when the stagnation temperature is taken into account, lower than the dissociation threshold of the molecules, and to have for each exit Mach number and stagnation temperature shape of nozzle. The method of characteristics is used with the algorithm of the second order finite differences method. The form of the nozzle has a point of deflection and an initial angle of expansion. The comparison is made with the calorically perfect gas. The application is for air.

Bruel, P.;Naimanova, A. Zh.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040050

Abstract The interaction of a planar supersonic air flow with the hydrogen jet injected perpendicularly across the slot from the duct walls is studied numerically. An algorithm is constructed for solving the Favre-averaged Navier — Stokes equations for the flow of a thermally perfect multicomponent gas based on the ENO scheme. The influence of the jet Mach number and the ratio of the jet and flow pressures on the shockwave structure of the flow and the jet penetration depth is shown.

Zudov, V. N.;Tretyakov, P. K.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040062

Abstract In the present paper, we report the results of an experimental study of the interaction region of a planar compression shock produced by a wedge in stream with the wake formed behind a cocurrent gas jet (H2, air, or Ar) injected into the flow. Depending on the gas jet parameters, three modes of interaction could be distinguished: a strong interaction, observed when the flow velocity in the wake was subsonic; a moderate interaction, observed when a subsonic flow region, bounded by a shock of almost conical shape, formed in the vicinity of the compression shock; and a neutral interaction. Three-dimensional non-stationary Euler equations were solved to numerically examine the interaction of an axisymmetric jet with an oblique shock wave. The obtained interaction regimes were found to be in a reasonable agreement with experimental data.

Naumov, I. V.;Okulov, V. L.;Sorensen, J. N.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040074

Abstract Results on investigation of vortex unstable breakdown are presented. The structure of vortex multiplets was visualized in a vertical cylindrical container made of transparent organic glass of the optic quality with the inner diameter of 288 mm and rotating upper lid. Visualization was performed for different heights of this cylinder. The working liquid was 80-percent water-glycerin mixture, and small air bubbles were used as the tracers. The lid was rotated with a constant angular velocity under the studied conditions, and air was accumulated in the zones of decreased pressure on axes of vortices. Visualization of flow structure for unstable swirl flows and cylinder aspect ratios from 3.2 to 5.5 allowed first identification of these regimes as multispiral breakdowns with formation of helical-like vortex duplets, triplets, and quadruplets.

Perepelitsa, B. V.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040086

Abstract Results of visual studies of the flow structure of the air jet in a channel with corrugated wall are presented. The studies have been carried out in the laminar and turbulent flows. The typical large-scale structures and zones of intensive turbulent mixing have been determined in the flow. The general scheme of the flow is suggested.

Rudyak, V. Ya.;Minakov, A. V.;Gavrilov, A. A.;Dekterev, A. A.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040098

Abstract A method is proposed for modelling fluid flows in microchannels. The method is tested on the known experimental data on studying the flows in microchannels with the aid of the micro-PIV. The flow regimes in micromixers of the Y- and T-types are studied. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds and Péclet numbers as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings are analysed. A T-mixer is proposed as an active technique of mixing, in which the flow rate in one of the inlet channels varied according to the harmonic law. The dependence of the mixing efficiency on the frequency of the variation of the flow rate and its amplitude is established.

Boiko, A. V.;Kornilov, V. I.

2010 Thermophysics and Aeromechanics

doi: 10.1134/S0869864310040104

Abstract Based on fine measurement of time-averaged data of hot-wire anemometer we have developed the method determining local values of skin-friction coefficient in the vicinity of the wall on the planar porous surface at the flow past which the noncanonical turbulent boundary layer is formed. The method may be applied at investigation of the efficiency of various effects on the incompressible boundary layer, in particular, with microblowing of air where usage of direct methods of friction determination is complicated.