Journal of Applied Mechanics and Technical Physics最新文献

Optimization of tangential jet blowing on the upper surface of a supercritical transonic airfoil under buffet conditions was carried out. Two-dimensional unsteady Reynolds-averaged Navier–Stokes equations were solved to simulate the flow past the airfoil. The Spalart–Allmaras turbulence model was used to close the equations. The location of the slot nozzle and the intensity of the jet blowing from it were varied. The optimal location for blowing with minimum jet intensity to suppress buffet was determined.

A problem of mathematical simulation of a fuel element region, including many fuel pellets and a cladding fragment, is considered in an axisymmetric formulation. It is assumed that the cladding is a thermoelastic-plastic body and that the pellet is a thermoelastic body with account for cracking of the material. Different variants of the domain decomposition method are used to numerically simulate the thermal and mechanical contact of pellets with each other and with the cladding. Calculation results are presented, in which the region containing ten pellets reaches a nominal power and the effect of pellet cracking on the thermomechanical state of the fuel element is estimated.

Investigations (mainly those performed by the authors) of air blowing through a perforated section on a body of revolution with a large aspect ratio in an axisymmetric incompressible flow are summarized. Result of numerical and experimental studies of the flow properties, efficiency of the turbulent boundary layer control and prospects of using it for a body of revolution at low subsonic velocities equivalent to the take-off and landing regimes for a modern subsonic cargo aircraft are analyzed.

A periodic flow of an incompressible fluid around plates at high Reynolds numbers and low Keulegan–Carpenter numbers is considered. Energy dissipation per oscillation period and drag coefficient of plates are determined. The two-dimensional problems under study are a problem of translational and angular oscillations of a flat plate and a plate shaped as a circular arc, a problem of translational oscillations of a circular cylinder with symmetrically located edges, a problem of angular oscillations of cruciform plates, and a problem of a periodic flow around an inclined edge on a flat wall. Also, a three-dimensional problem of translational and angular oscillations of a thin circular disk is considered. All the resulting dependences for energy dissipation and drag coefficient are presented in analytical form via velocity intensity factors, which characterize the velocity singularity at the sharp edges of the plates with a potential flow around an ideal fluid. Some of the resulting dependences are compared with the available numerical and experimental data.

This paper describes a new method for performing the time-frequency analysis of particle image velocimetry data with account for surface constant-temperature anemometer sensor readings. This method is based on calculating correlation coefficients between particle image velocimetry data and constant-temperature anemometer data, previously filtered in a given frequency range. This approach makes it possible to obtain data on the unsteady characteristics of flows throughout the entire measurement range in a frequency range whose boundaries extend beyond the boundaries of the particle image velocimetry frequency range. The proposed method is applied to study nonstationary processes in a region where a shock wave interacts with a boundary layer at a Mach number M = 1.43.

This paper presents the results of a study of the influence of various sources of magnetic field on the size of droplets formed in microfluidic flows. Direct and reverse emulsions in a microfluidic flow focusing were obtained using magnetic fluids based on oil and water which are a continuous phase. Non-magnetic inclusions of various volumes were formed depending on the selected parameters: continuous phase flow rate, magnetic field configuration, and the position of the magnet relative to the axis of the device.

A flow around a symmetrical thick teardrop airfoil in a nonstationary formulation is numerically modeled at Reynolds numbers (mathrm{Re}=10^4{-}10^5) and in a range of angles of attack (alpha=~-10{-}10^circ). Calculations are based on the approximation of unsteady Reynolds-averaged Navier–Stokes (URANS) equations using the implicit large-eddy simulation (ILES). The URANS approach requires that the position of a laminar-turbulent transition is determined using (k{-}kl{-}omega) and (k{-}omega{-}gamma{-}mathrm{Re}_theta) models, as well as ((k{-}omega))-SST models with a given laminar flow region. It is shown that the flow pattern and aerodynamic characteristics of the airfoil are greatly affected by the position of the laminar-turbulent transition region. It is suggested by the comparison of the results obtained using the ILES approach with experimental data that they are in good agreement. The URANS based calculations do not yield results consistent with experimental data. Fixing the laminar-turbulent transition point in the URANS calculation in some cases make it possible to correct the results.

The sizes and rise velocity of bubbles in a stationary liquid in an inclined channel with a circular cross-section at different gas flow rates through a capillary were determined (3.0–5.5 ml/min). The size and velocity of gas bubbles were studied by shadow photography. It is shown that in the range of channel inclination angles 40–60°, the formation of stable bubble structures—clusters consisting of bubbles of the same size (1.5–1.8 mm) — is possible. In regimes without the formation of chain clusters, the average diameter of gas bubbles increased (2.0–2.2 mm) due to their coalescence.

This study touches upon the characteristics of liquid (diesel) fuel combustion in a high-velocity jet of superheated steam in the combustor of a hot water boiler, the thermal power of the burner being approximately equal to 40 kW. It is shown that the burner based on the steam fuel atomizing technology meets modern technical and environmental standards and is quite advantageous in relation to its analogs. It is revealed adding steam makes it possible to cause a severalfold decrease in CO and NO(_x)concentrations in combustion products. At the same time, the amount of carbon monoxide and nitrogen oxide emissions when using this burner is quite smaller (2.5- and 1.4-fold, respectively) than when using a Weishaupt burner. Recommendations for optimizing the operation of such devices are presented.

The breakup of a jet consisting of two coaxial jets of immiscible liquids has been studied experimental with varying phase flow rates. Distilled water and a mixture of polymethylsiloxanes were used as working liquids. Jet breakup regimes, the types of capsules formed, and the sizes of single-core capsules formed under the influence of capillary instability were determined. The natural frequencies of surface instability were measured.