Home – Home – Jornals – Thermophysics and Aeromechanics 2004 number 3

Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear stage of the laminar-turbulent process in shear flows are presented. The flow behavior in the course of spatial evolution of streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical and numerical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaky structure are demonstrated, such as transverse and streamwise modulation of the structure by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady (-type structures localized in space in both cases.

In the present study, we examined the distributed (along the streamwise coordinate) excitation of 3D Tollmien ( Schlichting (TS) waves by weak non-stationary free-stream vortices propagating along the edge of a thickening laminar boundary layer obtained on a plate with 2D small-height surface roughness. We performed a theoretical analysis of the operating excitation mechanism and, based on this analysis, introduced functions (coefficients) of distributed receptivity for the flow and proposed an experimental procedure for determining these functions based on fitting experimental distributions with analytical solutions. Under conditions of controllable disturbances, we performed a quantitative experimental study of Blasius boundary-layer receptivity to non-stationary free-stream vortices with wall-normal vorticity vector in the presence of 2D streamwise-periodic surface roughness. A detailed thermoanemometric study of disturbances in the free stream and in the boundary layer was carried out, and the shape (waveform) of the surface roughness was measured. By the point-source technique, we experimentally examined the linear 3D stability characteristics of the flow under study necessary for obtaining the coefficients of distributed receptivity. The free-stream vortices were found to excite 3D TS waves via two receptivity mechanisms: on the smooth surface and through the interaction of free-stream vortices with surface roughness. Based on the new approach, we experimentally determined the amplitudes and phases of the coefficients of distributed vortical receptivity of both above-indicated types as functions of spanwise wavenumber. The flow is found to be most sensitive to quasi-2D vortical disturbances. At the same time, for the chosen streamwise wavenumber of surface roughness, it is 3D TS waves that are excited most efficiently. For these waves, a wavenumber resonance is possible, proved to play a fundamental role in the generation of instability waves. A large width of this resonance in the spectrum of spanwise wavenumbers is demonstrated.

The characteristics and specific features of development of streamwise vortex structures obtained by means of injection (suction) are studied under conditions of a model experiment in the boundary layer on a nonswept wing. The studies were performed in a subsonic low-turbulent wind tunnel with a hot-wire method used to register the disturbances. In the case of generation of controlled disturbances (streaky structures) in the boundary layer on a nonswept wing, high-frequency wave packets (precursors) are found to be excited near the fronts of the streamwise disturbances. The dynamics of development of the wave packets is considered with respect to the following parameters: velocity gradients at the leading and trailing fronts of the streamwise disturbance and methods of its generation (injection/suction). An analogy is drawn between the precursors and packets of Tollmien ( Schlichting waves.

Results of experimental investigations of an incompressible turbulent boundary layer formed on a flat plate under the action of a viscoelastic (compliant) coating made of synthetic rubber are discussed. It is shown that the examined specimen of the viscoelastic coating with prescribed properties ensures a 5

The experimental results are presented for study of gravitation-driven film flow in a model of cubic packing of balls bed. The velocity field was measured with PIV technique (Particle Image Velocimetry) using the transparent elements of the ball bed as components of optical system. The pioneer measurements of instant and averaged velocity were performed in a

Wave characteristics of the water film flow over a vertical plate with a heater of 150x150 mm were measured by the capacitance method. The influence of heat flux density on the wave flow of a liquid film forms rivulets and a thin film between them. In the interjet area wave amplitude and thickness pulsation frequency decrease. Three-dimensional waves propagate along the jet crests. Wave amplitude is determined by a change in liquid film thickness under the action of thermocapillary forces. Relative amplitude is almost independent of the heat flux.

The main regularities of supersonic heterogeneous flows (gas

The structure of hydrogen flame combustion zones in an nonisobaric supersonic high-temperature air jet is experimentally studied. Reliability of results obtained under adopted experimental conditions by registering visible emission from the air-hydrogen flame is confirmed. With the help of a high-speed recording system, the dynamics of combustion zones developing in peripheral regions of the flame has been revealed. A direct correlation is shown to exist between the combustion zones in the flame and the gasdynamic structure of the outer nonisobaric air jet. The travel velocity of large-scale combustion zones is estimated. The mechanism of flame-tail instability is unveiled.

The process of plasma thermochemical activation of fuel mixture in a chamber with plasmatorch was studied numerically. Experimental data required for verification of applied mathematical models were obtained using a plasmatorch with a straight-flow burner. Values of temperatures, gas, and solid particle velocities as well as concentration of gaseous components along the chamber with plasmatorch were calculated, temperature, velocity and concentration profiles were obtained in the chamber for gas and coal particles. Numerical results satisfactorily correlate with experimental data.

The numerical modelling of convective heat and mass transfer processes has been performed in real furnace chambers at the burning of both conventional fuel and the fuel treated in electric arc plasmafuel system mounted on the burners. The obtained results are presented as the fields of temperature and concentrations of the main components. The distributions of main parameters of combustion process are compared for two regimes of operation of furnace chambers. An analysis of the results obtained shows a positive influence of the plasma preparation on the basic kinetic and thermophysical characteristics of the process.

18 July, 2004 was the 90th anniversary of the famous scientist, Academician Samson S. Kutateladze. The history of thermophysics is inseparably linked with the name of S.S. Kutateladze. He made a priceless contribution to development of science on heat and mass transfer.

5 August, 2004 was the 60th anniversary of the Honored Scientist of Russian Federation, the Laureate of State Prize of RF in the field of science and technology, Doctor of Technical Sciences, Professor Victor I. Terekhov.