Hot-wire visualization of breakdown to turbulence in complex flows

The nonlinear stage of breakdown to turbulence is a strongly three-dimensional process and represents a difficult task for experimental studies. Investigation of laminar-turbulent transition in aerospace applications additionally involves a complex base-flow with pressure gradients and secondary velocity components resulting in successive increase of necessary measurements. The developed hot-wire visualization technique offers a possibility for an advanced analysis whilst retaining the advantages of traditional visualization methods and is especially suitable for resolving such complex flows. Thanks are due to the Royal Swedish Academy of Sciences, the Swedish Energy Agency (Energimyndigheten). The work was financially supported by the President of the Russian Federation (Grant No. NSh-964.2003.1), the Russian Foundation for Basic Research (Grant No. 05-01-00034) and Ministry of Education and Sciences of the Russian Federation (Grant No. RNP.2.1.2.3370).     

Matrix formulation of hydrodynamics and extension of ptolemaic flows to three-dimensional motions

A new matrix formulation of Lagrange hydrodynamic equations is proposed. Exact solutions of those equations are obtained in matrix form. It is found that precession of vortex lines around some fixed axis in space is a general property of the flows described by those solutions. Two types of fluid motion are studied. Flows of the first type have straight vortex lines, and their particle trajectories are windings on toroidal surfaces. The other flows have plane particle trajectories, and their vortex lines are arbitrarily shaped plane curves. All these motions are shown to be three-dimensional generalizations of plane Ptolemaic flows [1,2].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 6, pp. 783–796, June, 1996.The authors express their gratitude to the Russian Foundation for Fundamental Research for support of these investigations under Grant No. 96-01-00585 and to INTAS Foundation for support under Grant No. 93-1373.     

Turbulent gas-dispersed flow in a pipe with sudden expansion: numerical simulation

A mathematical model was developed to simulate two-phase gas-dispersed flow moving through a pipe with axisymmetric sudden expansion. In the model, the two-fluid Euler approach was used. The model is based on solving Reynolds-averaged Navier — Stokes equations for a two-phase stream. In calculating the fluctuating characteristics of the dispersed phase, equations borrowed from the models by Simonin (1991), Zaichik et al. (1994), and Derevich (2002) were used. Results of a comparative analysis with previously reported experimental and numerical data on two-phase flows with separation past sudden expansion in a plane channel and in a pipe are given. This work was supported by the President of the Russian Federation through the Foundation for Young Candidates of Sciences under Grant MK-186.2007.8 and by the Russian Foundation for Basic Research (Grants Nos. 05-08-33586 and 06-08-00967).     

Experimental study and mathematical modelling of heat transfer processes in heat accumulating media

Experimental results on reversing non-stationary heat transfer are presented for filtration of an air flow through an immobile heat accumulating medium consisting of lead (D = 2.0, 3.5, and 4.5 mm) and glass (D = 3.2 mm) balls. The studied device imitated the cyclic modes of heat regeneration in the ventilation system for domestic and office rooms. Dependency between the time of flow switching and Re number was measured. The mathematical model describing heat transfer between a gas flow and an immobile layer of balls was developed. Good correspondence between the experimental data and calculation results is observed for high Reynolds numbers. For low Re numbers the effect of heat losses is considerable, and experimental time of flow switching is shorter than the calculation one. The work was financially supported by the President of the Russian Federation (Grant No. NSh 6526.2006.3), Russian Foundation for Basic Research (Grant No. 06-08-00982), Foundation “Global energy” and Program “Energy saving of SB RAS”.     

Development of laminar-separating-flow perturbations on a wavy wing

The development of velocity perturbations at laminar boundary-layer separation from a wing with wavy surface has been examined. Experiments were carried out to identify flow features displayed by the spatially periodic flow structure. An analysis of the linear stability of measured velocity profiles is performed. As a result of the analysis, the influence of surface waviness on the frequency range and growth rates of instability waves was investigated, with a good agreement between calculated and experimental data. This work was supported by the Ministry of Education and Science of the Russian Federation under the Program “Development of Higher-School Scientific Potential” for the years 2006–2008 (Projects RNP 2.1.1.471 and RNP 2.1.2.3370), and also by the Russian Foundation for Basic Research (Grant No. 07-08-00164).     

Improvement of gas-jet ejector discharge characteristics with heads,chevrons, and tubs

Properties of gas-jet ejectors with converging mixing chamber operated under critical and subcritical flow conditions are examined. Establishment of the critical operation mode in such ejectors started up with and without the secondary gas flow is considered. The mechanism underlying the emergence of flow pulsations at low rates of the low-head flow is described. Results of an experimental study aimed at the improvement of ejector discharge characteristics by chamber-length reduction and related mixing enhancement are reported. As flow-mixing elements, slotted heads, chevrons, and tubs are considered. The best discharge characteristics were obtained with nozzles provided with tubs. This work was supported by the Russian Foundation for Basic Research (Grant No. 05-08-01215) and by the PRE “Laser systems” (Contract No. 512-2005).     

Effect of riblets on nonlinear disturbances in the boundary layer

Results of experimental investigations of the nonlinear stage of sinusoidal and varicose instability of a streaky structure, which leads to multiplication of streaky structures and origination of coherent structures (such as Λ-structures), are presented. Riblets suppress the intensity of streaky structures, stabilize the flow against the development of the secondary high-frequency instability of streaky structures, and, for this reason, delay spatial turbulization of the flow. The results of these investigations can be useful for understanding the flow structure in such situations and for possible controlling of the coherent structures aimed at flow stabilization. This work was supported by the President of the Russian Federation (Grant No. NSh-964.2003.1) and by the Russian Foundation for Basic Research (Grant No. 05-01-00034).     

Wall shear stress in an upward slug flow in a vertical tube

This paper deals with wall shear stress in an upward gas-liquid slug flow inside a vertical tube. Local characteristics were measured by the electrodiffusion method. The method of conditional averaging over realization ensemble was used, and this allows distinguishing large-scale structures on the background of turbulent pulsation of liquid. While averaging, each slug velocity measured by a double probe of electric conductivity was taken into account. Averaged distributions of shear stress over the wall under a gas slug were obtained for different mode parameters. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-01-00328) and the Russian Science Support Foundation (Grant “The Best Post-Graduate of RAS-2006”).     

Heat transfer peculiarities in separated flow past an oblique rib under different external turbulence

Results of an experimental study of turbulent flow past a flat rib installed at an angle to the free-stream direction are reported. In the experiments, external flows with two different turbulence numbers were used, and the angle of rib inclination to the free stream was varied from 50 to 90°. The experiments were performed for ribs of various heights under conditions with natural and high (13.4 %) free-stream turbulence levels. Visualization tests were performed to elucidate the vortex formation pattern and the direction of flow streamlines. Deformations of the recirculation region and secondary-vortex zone as well as enhanced effects due to 3D flow structure observed on decreasing the angle ϕ, and also notable restructuring of the flow at a high free-stream turbulence intensity, were identified. A comparison between pressure coefficients in different longitudinal sections of the channel is reported for ribs of various heights installed at various angles ϕ. The influence of rib inclination angle, rib height, and free-stream turbulence number on local heat-transfer coefficients and heat-transfer intensification is analysed. This work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00300).     

Interaction of Tollmien—Schlichting waves in compressible boundary layer

The computations of nonlinear development of pairs of oblique Tollmien — Schlichting waves in a boundary layer on a plate are carried out for M = 2 using the non-local (parabolized) stability equations. Besides such waves, a harmonic engendered by them is involved in the interaction. The work was supported financially by the President of Russian Federation (Grant NSh No. 2005-RI-112/001/742) and by the Russian Foundation for Basic Research (Grants Nos. 05-01-00079 and 05-01-00176).     

Modelling of streaky structures and turbulent-spot generation process in wing boundary layer at high free-stream turbulence

Results of an experimental study of turbulent breakdown in gradient boundary layer at high freestream turbulence are reported. For the first time it is shown that, like the flat-plate boundary layer, the wing boundary layer at high freestream turbulence is modulated with streaky structures. One of possible mechanisms underlying the generation of turbulence spots in wing boundary layer is modelled assuming the interaction of streaky structures with high-frequency waves. Qualitative and quantitative data concerning the evolution of streaky structures in swqpt-wing boundary layer and in swept-wing boundary layer are presented. Certain differences between the evolution of streaky structures in wing boundary layer and in flat-plate boundary layer are revealed. This work was supported by the President of the Russian Federation (Grants NSh-454.2008.1, MK- 101.2007.1), by the Russian Foundation for Basic Research (Grant No. 05-01-00034), by the Ministry of Education and Science of the Russian Federation (Grant No. RNP 2.1.2.3370), and by the Russian Government (State Contract No. 02.513.12.0043).     

Experimental and theoretical investigation of boundary layer perturbations on a low-aspect-ratio wing

Laminar-turbulent transition in a boundary layer of low-aspect-ratio wing was investigated. Experiments clarifying the flow structure, its mean and oscillatory characteristics were carried out accompanied by linear stability analysis of the wind tunnel data on the laminar flow velocity profiles. Theoretical results obtained in a parallel flow approximation are in a good agreement with the experimental data on disturbances evolution at the initial stage of transition to turbulence. The study was supported by the Ministry of Education and Science of the Russian Federation (Grant No. RNP 2.1.1.471) and Russian Foundation for Basic Research (Grant No. 03-01-06145)     

Spatial structure of the flow at round jet outflow into a narrow channel

Results on visual studies of the flow structure in case of the round submerged jet in a narrow channel are presented. These studies were carried out for the laminar and turbulent flows. The typical large-scale structures and zones of intensive turbulent mixing were identified in the flow. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00417-a).     

Experimental study of pressure and density of saturated and superheated vapor of refrigerant R-236ea from 20 to 150 °C

The saturation pressure, pressure and density of superheated vapor of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea, R-236ea) were studied by an isochoric piezometer within the temperature range of 294–423 K up to the pressure of 4.0 MPa. The uncertainties of temperature, pressure, and density measurements were estimated as ±20 mK, ±1.5 kPa, ±(0.1–0.2) %, and ±(0.1–0.2) %, correspondingly. The purity of studied samples was 99.68 mass %. The obtained experimental data are shown as tables and analytical equations. Coefficients of the virial state equation were calculated for R-236ea on the basis of these data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-02-16355).     

Nonlinear instability research of longitudinal structure generated by roughness in unswept wing boundary layer

The results of experimental study of a nonlinear varicose instability of the streaky structure generated by roughness element in unswept-wing boundary layer are presented. Features of the varicose breakdown of longitudinal steady streaky structure such as modulation of structure in transverse and streamwise directions by secondary disturbance, occurrence of the new streaky structures and A-structures downstream are shown. Spatio-temporal pictures of the hot-wire visualization of flow during spatial evolution of the streaky structures under influence of secondary high-frequency disturbance are discussed. Features of the adverse pressure gradient influence upon processes of the nonlinear varicose instability evolution and flow structure are revealed. Essential influence of the adverse pressure gradient on evolution of disturbances in shown. Comparison of varicose instability of the streaky structures generated in two different ways (the roughness element as in the given work, and continuous air blowing as in the earlier published work) is the carried out. The work supported by the Ministry of Education and Science of the Russian Federation (Grant No. RNP. 2.1.2.3370) and by the Russian Foundation for Basic Research (Grant No. 05-01-00034).     

On the quantization of SU(3) skyrmions

The quantization condition derived previously for SU(2) solitons quantized with SU(3) collective coordinates is generalized for SU(3) skyrmions with nonzero strangeness content. Quantization of the recently discovered dipole-type configuration with large strangeness content is considered as an example. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 391–396 (25 September 1996) This study was supported by the Russian Fund for Fundamental Research, Grant 95-02-03868a and by Volkswagenstiftung, FRG. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Structure of the electromagnetic fields of loop radiators in magnetized plasmas over the whistler frequency range

The role of different sections of the spatial spectrum of whistler waves excited by a loop antenna in the formation of an electromagnetic field structure is investigated experimentally and theoretically. Primary attention is given to the intermediate range of distances between the source and the observation point.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 2, pp. 192–202, February, 1996.T. M. Zaboronkova, A. V. Kostrov, A. I. Smirnov, and A. A. Shaikin are grateful to The Russian Foundation for Fundamental Research (Grant No.94-02-05447a) and the George Soros International Foundation (Grant No. NOP 300) for financial support. A. V. Kudrin is grateful to the Russian Fund for Fundamental Research (Grant No. 96-02-18666) for financial support.     

Surface instability of the liquid turbulent flows in the open inclined channels

The flow of a viscous liquid layer in an open inclined channel under the turbulent mode is considered in this paper. To describe turbulent viscosity, the Van Driest model is used. The spectrum of characteristic values of the problem on linear stability of a plane-parallel flow is studied numerically. Parameters of the maximal growth waves are found out, the surface tension effect is studied, and theoretical results are compared with experimental data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-33585a).     

Spatiotemporal evolution of the distribution function of electrons in sign-changing electric field

A numerical model for solving the Boltzmann unsteady non-local kinetic equation for the distribution function of electrons over energy is constructed. The Boltzmann equation for isotropic part of the distribution function written in natural variables the kinetic energy — the coordinate was solved by the pseudo-unsteady method. The model was applied for describing the spatiotemporal evolution of the distribution function of electrons in a uniform electric field. For a model distribution of the electric field with the “negative” value in the Faraday dark space and the “positive” value in the positive column of the glow discharge, the main macroscopic parameters of electrons are obtained, the diffusion mechanism of the electron current transfer in the negative electric field region is confirmed. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-02-00781-a) and by State Contract No. 02.513.11.3242.     

Thermal properties of liquid alloys of magnesium-lead system

The temperature variations of the density of liquid magnesium-lead alloys were measured by the gamma-method in the temperature range from the liquidus temperature to 950–1000 K for compositions of 19.11, 33.45, 52.46, and 83.06 at. % Pb. It is shown that within the estimated errors (0.25–0.30 %), the alloy density depends linearly on the temperature. Approximation dependences ρ(T) were obtained for every studied composition together with generalizing density-temperature and density-concentration dependences for the range of 0–100 at. % Pb. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00040).