Home – Home – Jornals – Thermophysics and Aeromechanics 2008 number 1

An experimental study of different control methods for hypersonic air inlets aimed at ensuring reliable starting of these apparatuses and improving their operating characteristics in the range of Mach numbers 2 to 8 is reported. Conditions for boundary-layer separation and possibilities for preventing this separation by using modified diffuser configurations and/or perforation bleedage are examined. An air-inlet model was tested for operation in an intermittent wind tunnel and in a blow-down wind tunnel respectively in the Mach-number ranges 2 to 6 and 5 to 8. Distributions of static and total air pressures on the walls of the model and in several cross sections were measured, together with air flow coefficients and total-pressure recovery coefficients. Perforation bleedage is shown to offer an efficient means to facilitate air-inlet starting. Perforation bleed has enabled a more than two-fold increase in the air flow coefficient on the model with sidewalls. A perforation-bleed panel installed closer to the air-inlet throat proved to be more efficient. The possibility of sudden starting of the air-inlet apparatus was checked in the intermittent wind tunnel; it was shown that, here, sudden starting could be realized. The data obtained in the intermittent wind tunnel proved to be consistent with data obtained in the blow-down wind tunnel with up to 150-ms blowdown time.

The effect of local periodic forcing in the form of blowing/suction through sequentially located annular slots on the features of the turbulent boundary layer formed on an axisymmetric body of revolution in an incompressible flow is studied experimentally. The Reynolds number based on the momentum thickness of the boundary layer ahead of the annular slot is 1362. The dimensionless amplitude of the forcing signal A₀ is set to be 0.4. The frequency of the forcing signal in the law-of-the-wall units is f⁺

The results are presented for experimental investigation of the peculiarities of the development of three-dimensional turbulent separated flows on a flat surface for the Mach number

Experimental data concerning the influence of initial conditions at the nozzle exit on the structure and development characteristics of round jets are reported. Features in the development of laminar and turbulent round jets emanating from variously elongated nozzles at identical Reynolds numbers are revealed. Smoke visualization pictures obtained for jets formed under different initial conditions (with different distributions of mean and pulsating flow velocities at the nozzle exit) are discussed. It is shown possible to make the zone of laminar flow in the jet stream more extended, and to delay the jet turbulization process in space, by making the flow-velocity profile more parabolic at the exit of elongated nozzle. Features in the development of vortical structures in a jet under an acoustic action are identified. It is shown that, for a turbulent round jet to be produced right at the nozzle exit, the nozzle length must be increased in excess of a certain value so that to provide for spatial growth of turbulent boundary layer thickness, finally ending in the formation of a fully turbulent flow velocity profile across the channel.

We consider the influence of the solar ultraviolet emission on the photoionization of the working body of drainage systems and microthruster units of a space vehicle, which leads to an increase in the decay of radio-waves of its radio systems. It is necessary to choose the working body of the microthruster units of the space vehicle orienting towards the substances with a low photoionization section (hydrazine, methyl alcohol, etc.). When choosing the working frequencies of radio systems it is necessary to orient oneself towards higher frequencies (hundreds and thousands of megahertz).

The field of application for the systems of high-altitude aerodynamics and typical problems solved are presented. The main requirements for these systems are formulated. Some methods for implementation of these requirements are shown by the example of RuSat system.

A single cell of the gas-liquid slug flow was studied. The flow around an immobile gas slug in a downflow of liquid and under its bottom was measured. The values of the wall shear stress and its pulsations were measured by the electrodiffusion method depending on a distance from the slug nose. It is shown that in a liquid film around a slug, turbulent pulsations are damped in comparison with a single-phase liquid flow. In the bottom part of a slug, where vortices are detached, turbulent pulsations exceed significantly the single-phase ones.

Results of numerical investigation of the boundary layer thickness on turbulent separation and heat transfer in a tube with an abrupt expansion are shown. The Menter turbulence model of shear stress transfer implemented in Fluent package was used for calculations. The range of Reynolds numbers was from 5× 10³ to 10⁵. The air was used as the working fluid. A degree of tube expansion was (D₂/D₁)² = 1.78. A significant effect of thickness of the separated boundary layer both on dynamic and thermal characteristics of the flow is shown. In particular, it was found that with an increase in the boundary layer thickness the recirculation zone increases, and the maximum heat transfer coefficient decreases.

Numerical modelling of a conjugate convective-conduction heat transfer in a rectangular region with a heat-release source was carried out in the presence of forced flow and mass exchange. The distributions of thermal and hydrodynamic characteristics, which describe the specific peculiarities of flow regimes under study, were obtained. The mutual influence of forced and free-convective flow was analysed. The scales of the effect of determining dimensionless complexes (Gr, Br, Re) on flow regimes were established. The evolution of analysed process was shown.

The influence of the plate inclination angle relative to the horizon on a distance between formed rivulets and breakdown of a falling water film was studied experimentally on a heater of 150×150 mm. Dependences of the distance between rivulets on the heat flux density and plate inclination angle were examined. In experiments two zones of influence of the heat flux on a distance between rivulets were revealed: at θ≥20

Electric characteristics of a high-frequency torch discharge measured by the resonance method are presented. It is shown that discharge capacity determined by the modified Neumann scheme is close to the value of electrostatic capacity. Capacity of discharge channel was calculated with consideration of propagation of a surface electromagnetic wave along this channel.

The role of electromagnetic forces and the forces of viscous friction with the arc plasma flow in the flow formation within the cathode melt is considered within the framework of numerical modelling; a comparative estimation of the separate influence of each of the above forces is carried out. The melt flow pattern is found to form mainly by electromagnetic forces. The character of the effect of electromagnetic forces is determined to a considerable extent by the ratio of the radius of cathode attachment of the arc on the melt droplet and the rod cathode radius.

The spatial combustion of turbulent jets in furnace devices is modelled numerically basing on equations for multi-component turbulent reacting gaseous mixtures. The dependencies are obtained for the influence of the secondary air velocity and composition of gaseous components on torch configuration at a diffusion combustion process. The effect of regime parameters on the increase in torch sizes, which arises at the interaction of secondary air with gaseous components, has been elucidated.

The experimental data obtained previously on the investigation of power characteristics and the possibility of the self-start of the Darrieus rotor are anlysed. These results are used at the design of new two-tier wind turbines with straight blades. The full-scale tests of two design variants showed the prospects for the development of wind turbines with the Darrieus rotor. At a reasonable design, they do not need any devices for the rotor orientation and start-up, are little sensitive to wind gusts and can have a high level of power characteristics, which is not inferior to the best samples of the units of propeller type.

Operation of the diametrical disc fan was studied experimentally at low (5- 50 torr) pressures in air. The effect of a drastic decrease in volumetric flow rate of the fan was revealed at pressures below 40 torr (flow rate crisis), what does not correlate with published data. The critical value of dimensionless parameter corresponding to flow transformation and formation of a closed flow inside a fan was determined and proved experimentally.