Vol 25, No 4 (2018)

The turbulent properties of a supersonic jet were studied related to a high level of pressure pulsation found in model jets of a reentry flight vehicle approaching the landing ground. This study comprised measurements of total pressure at a small-size target using a dynamic pressure probe placed in a free jet. The most comprehensive data about jet turbulence can be obtained by direct transformation of the pressure reading at the stagnation point near the target into the normalized velocity. The oscillogram of normalized velocity produces the velocity average value, root-mean-square value as well as turbulence intensity and turbulence spectrum. It was demonstrated that a high level of turbulence for a high-head jet retains along the supersonic core length and at the beginning of subsonic interval.

In this work, we present a numerical study of the laminar-turbulence transition flow around a symmetrical air-foil at a low Reynolds number in free flow and near the ground surface at different angles of attack. Finite volume method is employed to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. In this way, the Transition SST turbulence model is used for modeling the flow turbulence. Flow around the symmetrical airfoil SD7003 is numerically simulated in free stream and near the ground surface. Our numerical method can detect different aspects of flow such as adverse pressure gradient, laminar separation bubble and laminar to turbulent transition onset and the numerical results are in good agreement with the experimental data.

The possibility of drag reduction due to compliant coatings of viscoelastic silicone rubbers has been tested experimentally. For this purpose, a series of single-layer coatings of various thicknesses was made of a homogeneous material. The experiments were carried out in a high-speed cavitation tunnel of Pusan National University. Dynamic viscoelastic properties of coating materials were carefully measured. The range of flow rates and coating thicknesses was calculated assuming that the coatings can interact intensively with the dynamic structures of the turbulent boundary layer only in the region of frequencies of their maximum compliance. The predicted range of coating parameters and flow velocities, in which the coatings reduce drag, is compared with experimental data.

Spectral distributions of intensities, relative emissivity, and inverse radiance temperatures of an opaque, free-radiating object in a condensed state are used as the initial data. The methods of determining the thermodynamic (true) temperature corresponding to these distributions, when object emissivity is previously unknown, are considered. The advantages and disadvantages of each method and corresponding form of an initial data presentation are discussed. It is shown that the spectral distribution of inverse radiance temperatures gives the greatest information about the true temperature and emissivity of the measured object. The estimates of the temperature range to which the true temperature belongs are given based on the known experimental data for tungsten. The methods for additional verification of reliability of the obtained results are presented.

To describe the thermodynamic properties of xenon, a new fundamental low-parametric equation of state (in the form of reduced Helmholtz energy) is obtained with the help of the methods and approaches developed by the authors. It allows us to describe the thermal properties of gas, liquid, and fluid with a sufficiently high accuracy close to the accuracy of experiment in a range from the density in the ideal gas state to the density at the triple point, excluding the critical region. The caloric properties and speed of xenon sound are calculated without involving any caloric data, with the exception of ideal gas enthalpy. The values of isobaric heat capacity, sound speed, and other thermodynamic properties obtained by calculations are in good agreement with the experimental data.

A new numerical model for hydraulic fracturing has been developed. This model takes into account several simultaneous processes: pumping of proppant-laden slurry and its flow through the fracture, fracture growth with variable height and length, proppant settling, forming of proppant packing, and fluid filtration through this packing. Simulation experiments demonstrated that proppant particle diameter has significant influence on forming the proppant packing, fluid filtration through the packing, and, finally, on the fracture length and ultimate distribution of fracture width.

The article presents the research results of the influence of process parameters on the thermodynamic efficiency of expander-generator units, used as an alternative to throttling devices for technological reduction of pressure of transported natural gas at the plants of technological decompression of the gas supply system–gas distribution stations (GDS) and gas control points (GCP). The process parameters are the temperature of the outside air, the ratio between the pressures of the transported gas at the outlet and inlet of GDS and GCP, and the temperature of the gas heating before the expander. Various circuit designs of expander-generator units for generating either only electricity or electricity and cold are considered. Exergy efficiency is taken as a criterion for evaluating thermodynamic efficiency. The calculation results for the changes in flow exergy and exergy efficiency at changing process parameters are presented in graphical form. The thermodynamic efficiencies of throttling devices and expander-generator units are com-pared. It is shown that the replacement of the throttling device by the expander-generator unit for all the considered process parameters leads to an increase in the exergy efficiency of the stations for technological decompression of the transported gas in all the considered schemes of this unit inclusion: without heating the gas in the expander-generator unit, with heating the gas after the expander, as well as with heating before and after it.

The flow of a turbulent round submerged jet in far field has been considered. The modified Navier−Stokes equations have been derived with the aid of known self-similar properties of the time-mean flow as well as the spatial and temporal characteristics of the entire spectrum of the scales of turbulent fluctuations. A technique has been proposed for the numerical computation of these equations to describe a family of self-similar solutions in a cylindrical region with periodic boundary conditions in the longitudinal direction, and the velocity of the jet expansion enters the obtained equations explicitly as a parameter.

A mathematical model was developed for viscous incompressible medium; this model comprises a small parameter for regularization of ill-posed problem. Starting from the analogy with strain problems of axisymmetric laminar structures which include the elastic orthotropic and elastic volume-incompressible layers with a connection to viscous laminar fluid flow, we have developed a method providing a single algorithm for computation of velocity field, stresses, and other parameters of laminar composite material. The example of calculation for the binding agent flow during pultrusion formation is presented.