Home – Home – Jornals – Thermophysics and Aeromechanics 2008 number 3

The compressibility factor was calculated in a wide range of parameters including the critical region using the equations of state obtained previously for real gas and conditions and limitations formulated by the authors for the form (structure) of the equation of state. It was determined that maximal deviations of compressibility factor values calculated by these analytical equations from the experimental (tabulated) values occur mainly within the critical region. A corresponding correction was introduced into the initial equation, and the analytical equation accurately describing experimental data in a wide range of real gas state parameters, including the critical region, was derived. It was shown by the example of analysis of high-accuracy experimental data on thermal properties of helium in the critical region that data description by the proposed analytical equation is at least as good as that obtained by the equation of fluctuation theory (scaling). It is shown that the proposed equation meets the classical conditions at the critical point.

Speed of sound in the gaseous freon R-236ea with the purity of 99.68 mol. % has been measured by the method of ultrasonic interferometer in the range from 263 to 423 K and at pressures from 17 kPA to 4.2 MPa. Errors of temperature, pressure, and speed of sound measurement were estimated to be within +/- 20 mK, ± 1.5 kPa, and ±(0.1+0.2) % respectively. Temperature dependence of ideal-gas heat capacity of R-236ea has been calculated on the basis of the obtained data.

Experimental techniques for investigation of heat transfer in liquid mixtures of different types complimenting each other have been presented. The main attention is focused on the measurements under conditions of pulse heating. The paper opens the set of papers dealing with the elucidation of features characteristic of the heat transfer in pulse superheated mixtures, including metastable states with respect to the liquid-vapor and liquid-liquid equilibriums.

The gas motion through porous objects in the gravity force field with a non-uniform distribution of heat sources, which may arise as a result of natural or man-caused catastrophes (as the damaged power unit of the Chernobyl NPP), is investigated. The influence of different parameters of the heat-releasing zone on the process of cooling of such objects is analyzed with the aid of computational experiment. It is shown that the porous element heating is affected not only by the height of the heat-releasing zone and the heat-release intensity therein but also by the distance of the heat-releasing zone from the element inlet as well as by the width of the heat-releasing zone. The phenomenon of a reduction of the porous element heating with increasing distance of the heat-releasing zone from the porous element inlet is revealed. An ambiguous dependence of the porous object heating on the width of the heat-release zone is identified: at a growth of the heat-releasing zone width, the heating of the element may both increase and decrease depending on the distance of the heat-release zone from the element inlet.

Three-dimensional wave processes in vertically falling films of viscous liquid are considered. The 3D localized perturbations, which are studied insufficiently, are of a particular interest. The numerical method for watching evolution of initial perturbations was developed. The final stage of this evolution is formation of the 3D localized structures: solitons. The boundaries of 3D soliton stability were determined.

A Particle Image Velocimetry (PIV) system was used to perform an investigation into the effect of low concentration of dispersed phase on time-average and pulsating characteristics of the flow over the self-similar part of a two-phase jet emanating into ambient space filled with the same fluid. A phase discrimination procedure based on reflected intensity was introduced into routine practice. Distributions of mean and pulsating velocities in the carrier and dispersed phases of the gas-droplet jet were obtained. In spite of low concentration of the dispersed phase, large droplets present in the flow were found to reduce the intensity of velocity pulsations in the gas phase.

The PIV/LIF method was used to experimentally examine turbulent characteristics of a submerged gas-saturated axisymmetric impact jet. A novel method to analyze the dynamics of vortex formations is proposed, making it possible to obtain spectral characteristics of turbulent motion at low sampling frequency. A comparison of data obtained with theoretical models is reported.

Under conditions of a model experiment in nonswept-wing boundary layer, forerunner wave packets were obtained in the flow regions preceding the fronts of streaky structures. A model to describe the formation and development of the fronts is proposed. An external-flow pressure gradient is shown to be a necessary condition for forerunner growth. Besides, the spatial geometry of the forerunners and the evolution of this geometry in the course of downstream development of the wave packet were studied.

Results of parametric calculations of the total aeropropulsive characteristics and characteristics of acceleration of a small-scale high-velocity flying vehicle with an air-breathing engine are presented. Integral parameters of acceleration from the flight Mach number М_∞ = 4 to М_∞ = 7 are determined, namely, the time, required fuel stock, and range. A schematic configuration of the vehicle is considered, which allows studying the basic parameters, such as the forebody shape, the angles of surfaces of compression of the stream captured by the inlet, angles of external aerodynamic surfaces of the airframe, relative planform area of the wing panels, and relative area of the nozzle cross section. A comparative estimate of the effect of these parameters shows that it is possible to improve the characteristics of acceleration of vehicles of the type considered.

Aerodynamic characteristics of a sharp cone with the semi-apex angle of 15° are investigated by the methods of ballistic modelling in the Mach number range from 0.5 to 3.7, which are computed under the assumption of their almost linear behavior at the angles of attack up to 10°. Using the direct shadow pictures the geometric characteristics of near wake are measured and analyzed within the considered transonic and supersonic range. They provide the basis for semi-empirical computation of integral parameters of the base cavity: the pressure, density, and temperature.

The results are presented for numerical modelling of two-dimensional flows with large pressure gradients in a wide range of freestream parameters (М = 2−4, Re₁ = 5−30⋅10⁶ 1/m) and the intensities of perturbing factors. Computations were performed with the use of averaged unsteady Navier - Stokes equations of a viscous heat-conducting gas. The structure of a turbulent boundary layer at its passage through a single shock and a system of shocks of different strengths, which lie at a fixed distance from one another, was investigated numerically. In the case of the boundary layer passage through a system of shocks, the influence of the first interaction on the structure and separation properties of the boundary layer behind the second shock was investigated. The presence of a preliminary shock was shown to improve the boundary layer capability to withstand separation ahead of the secondary interaction region.

Based on the solution of unsteady Reynolds equations (URANS) closed with the aid of differential equations for shear stresses transport (MSST), the evolution of the vortex structure in a square cavity with a moving lid and an unsteady turbulent heat transfer in the air medium are computed while maintaining constant temperatures of the hot moving and cold motionless walls (Re = 5⋅10⁴). The phases of the development of dynamic and thermal processes are analyzed.

Specific features of laminar diffusion boundary layer on permeable surface with isothermal helium blowing into airflow are experimentally examined. Measured profiles of helium, nitrogen, and oxygen concentrations show that the proportion between the volume molar fractions of N₂ and О₂ varies across the boundary layer. At high intensities of helium blowing into air a difference from binary diffusion obeying the Fick law is observed. Our estimates show that, in boundary layer with foreign blowing, manifestation of effects due to multi-component diffusion is possible.

A physical and mathematical model is proposed and numerical investigations are carried out for processes of the deformation and non-equilibrium crystallization of a liquid metal drop with modifying refractory solid nano-inclusions at its collision with a solid substrate under the typical conditions of the gas-thermal and also plasma-sprayed coating. An analysis of the formation of splats is carried out depending on the substrate temperature.

A mathematical model is constructed for the bubble dynamics, in which the interphase surface variation is presented in the form of a series in spherical harmonics, and the equations are written with the accuracy up to the squared amplitude of the distortion of the spherical shape of the bubble. In the oscillation regimes close to periodic sonoluminescence of a single bubble in a standing acoustic wave, the character of air bubble oscillations in water was studied depending on the bubble initial radius and the amplitude of the liquid pressure variation. It was found that non-spherical oscillations of bounded amplitude can take place outside the region of linearly stable spherical oscillations. Both the oscillations with a period equal to one or several periods of the liquid pressure variation and aperiodic oscillations are observed. It is shown that neglecting the distortions in the form of spherical harmonics with large numbers (i > 3) may lead to a change of oscillation regimes. The influence of distortions on the bubble surface shape for the harmonics with i > 8 is insignificant.

The influence of acoustic resonators on the acoustic and propulsion performance characteristics of a ramjet ejector chamber under conditions with vibration hydrogen combustion was experimentally examined. In the study, resonators having identical throats and different cavity diameters were used. For fixed-volume resonators the best propulsion performance characteristics were achieved in the case in which the cavity diameter differed little from the resonator throat diameter.

The flow of reacting mixture of methanol and steam in a 2D microslot was studied numerically at activation of the reactions on the channel wall. This modelling was carried out in the framework of Navier - Stokes equations for a laminar flow of multicomponent compressible gas. Correlations between thermal, diffusion, and physical-chemical processes were studied under the conditions of intense endothermic reaction and external heat supply distributed along the channel. It is shown that not only the amount of heat supplied to the reaction zone is essential, but also the mode of heat supply along the channel length is important, which allows optimization of the compact reactor for hydrogen production.

Under consideration is the physical nature of the auto-scanning in plasmatorches with tube electrodes; the exclusive simplicity of this process comparing to the aeromagnetic and gas methods of scanning has been demonstrated.