Investigation of weakly-nonlinear development of unsteady Görtler vorticesBoiko, 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 %).
Effect of stagnation temperature on the supersonic axisymmetric minimum length nozzle conception with application for airZebbiche, 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.
Interaction of shock waves with a jet wake during gas injection into supersonic streamZudov, 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.
Diagnostics of spatial structure of vortex multiplets in a swirl flowNaumov, 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.
Modelling of flows in micromixersRudyak, 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.