Journal of Applied Mechanics and Technical Physics最新文献

This paper presents the results of experiments to strengthen the surface of a fluoroplastic composite by creating a protective layer. The protective layer was formed by detonation spraying of VSNGN-85 powder consisting mainly of WC (81.56 wt %) and Ni (10.6 wt %). The granulometric and morphological properties of VSNGN-85 powder were studied, and its X-ray diffraction analysis was carried out. Optimal spraying modes for obtaining a dense coating 100–115 (mu )m thick were determined. X-ray diffraction analysis showed the presence of WO₃ tungsten oxide and NiWO₄ (II) nickel tungstate in the coating. The microhardness of the composite material with the protective coating was found to be 48 times higher than the microhardness of the composite without coating. The applied coating increases the life of the fluoroplastic composite, improves its strength, and slows down its oxidation, corrosion, and thermal degradation.

This paper presents the results of experimental and numerical simulations of the interaction of plane shock waves with gas-permeable cellular porous barriers that are uniform in thickness or consist of layers of material with pores of different diameters. The experiments were carried out in a shock tube at shock-wave Mach numbers ({text{M}} = 1.2{kern 1pt} - {kern 1pt} 1.8). Highly porous cellular nickel was used as a gas-permeable material. In the numerical simulation, such cellular porous materials are described by a toroidal model of porous media. The mechanism of formation of reflected waves was determined. It is shown that, in the presence of highly porous gas-permeable cellular barriers, there is a decrease in the intensity of waves reflected directly from the structural elements of the material and the intensity of waves reflected from the rear end of the shock tube. Reflected waves are most effectively suppressed by combined barriers composed of material layers with pores of different diameters.

A history of development of various cycloidal rotors used as aircraft propellers is presented. The operating principle of a pitching-blade cycloidal rotor is described. Different papers on this issue are reviewed, quantitative data are summarized and analyzed, and the most important parameters affecting the characteristics of a pitching-blade cycloidal rotor are identified. Optimal values of the main parameters for improving the characteristics of a pitching-blade cycloidal rotor are obtained. A method for the engineering evaluation of the thrust of a pitching-blade cycloidal rotor is proposed.

An approach is proposed for simulating and evaluating the parameters of thin-walled elastic open shells and plates under postbuckling in large. A finite element model of the longitudinal bending of such a plate with fluted section is considered. A quasi-zero stiffness effect of the plate is numerically modeled. And then an effectiveness of this plate as an elastic element for a vibration isolating mechanism is performed. The validation of the finite element model and an assessment of control possibility the quasi-zero stiffness of the plates were performed by comparison of the results of analytical modeling and physical experiment. The results demonstrate a possibility for a widespread use of such elastic elements in vibration isoltuion systems for the ground and airborne equipment..

The properties of honey are studied experimentally. It is shown that honey becomes less viscous as with an increase in its moisture content or temperature. Close results are obtained when measuring the surface tension coefficient of white honey using several methods: the drop weight method, the capillary rise method, and the air bubble detachment method. A formula is derived that allows one to estimate the dynamic viscosity of the fluid using the known surface tension coefficient and the known air bubble shape recovery rate in a fluid after the stretching the bubble twice its size at the same measurement temperature.

This paper touches upon the formation of thermomagnetic convection in a stratified magnetic colloid that fills up a Hele–Shaw cell placed in an external nonuniform magnetic field and heats up from the side of a narrow edge in such a way that the constant field strength gradient is codirected with the temperature gradient. The Galerkin method is applied to obtain critical magnetic Rayleigh numbers for the cases of monotonous convection and oscillatory convection arising due to the nonuniformity of the concentration of magnetic nanoparticles caused by thermal diffusion and magnetophoresis. In the case of oscillatory instability, the dependence of the neutral oscillation frequency on the mixture separation parameter and the concentration Rayleigh number is determined. For supercritical monotonous and oscillatory convection regimes, the stream function, temperature, and concentration distributions are presented, and the behavior of the amplitudes of various spatial harmonics is investigated.

The propagation of disturbances generated by a heat source in a supersonic boundary layer interacting with an oblique shock wave is studied by direct numerical simulation. Calculations are performed using the HyCFS-R hybrid code. The generation and evolution of unstable boundary-layer disturbances, the effect of the incident shock wave on the development of disturbances and the effect of disturbances on boundary-layer separation and flow development in the regions of separation and laminar-turbulent transition are investigated. The influence of heat pulse duration on the generation and development of unstable waves in the boundary layer and the interaction region is examined. The generation of disturbances by a pair of sources located some distance apart is considered. Decreasing the heat pulse duration is shown to lead to an increase in the amplitudes of the first and second harmonics of the fundamental unstable mode. As result, the spectrum of disturbances in the interaction region changes and the flow transition to turbulence speeds up, leading to a decrease in the size of the separation region.

The interaction of a shock wave with a boundary layer on a half-airfoil model has been studied. Experiments were performed in a wind tunnel at a freestream Mach number ( approx {kern 1pt} 0.75) and a stagnation pressure ({{P}_{0}}{{ = 10}^{5}}) Pa. The half-airfoil model was mounted on the wall of the test section of the wind tunnel. Pressure distributions on the model surface were obtained using pressure sensitive paints and pressure taps. Visualization of the surface streamlines on the model by means of oil flow visualization technique and measurements of surface temperature distribution using infra red CCD camera were performed. Numerical simulation of the flow was performed with experimental parameters using the Reynolds-averaged Navier–Stokes approach. The three-dimensional flow structure was analyzed, and significant differences were found between the measurement results and numerical simulation data for flow in the corner separation regions.

The paper describes an experimental study of the process in which a cluster of monodisperse drops of isoparaffin oil rises to the surface in distilled water in a range of Reynolds numbers Re = 200–800. It is shown that the initial volume concentration of drops in the cluster is one of the main parameters determining its dynamics. The study also touches upon the motion of two types of clusters, characterized by the presence or absence of collisions of the drops contained in it. Experimental dependences of the rising velocity of the drop cluster on the Reynolds number are obtained for different values of the initial volume concentration of drops. The limiting value of the initial volume concentration of drops is determined, corresponding to the onset of cluster motion with a velocity exceeding the velocity of a single drop.

The main objective of the present study is to apply spanwise periodic rows of cylindrical turbulators to investigate the mechanism of forced turbulization of a swept-wing boundary layer with predominant cross-flow instability. The experiments are carried out using hot-wire anemometry in a low-turbulence wind tunnel at the Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, at low subsonic freestream velocities on a 25-degree swept-wing model. The results of detailed precision measurements of the mean and fluctuating flow structure are obtained in a wide spatial region in 12 different measurement regimes for five types of turbulators (and without them) at two flow velocities. The studied range of Reynolds numbers based on the cylinder height lies between 565 and 3613. This is the first part of this study, and it describes the main scenarios of turbulator-induced transition to turbulence. The high efficiency of turbulators is demonstrated. This study continues in part 2 [1].