Vol 59, No 6 (2018)

This paper describes a laboratory study of the behavior of turbulent boundary layers in the presence of two-dimensional hills. Flow measurements of the developing turbulent boundary layer on a single hill and on two successive hills are performed in a wind tunnel. The mean and turbulent velocities are measured by PIV anemometry. The results provide a detailed description of the inner layers upstream and above the hills in the separation recirculation zones. The deduced mean and fluctuating velocity fields are compared for the flow in the presence of a single hill and two successive hills located on smooth and rough walls.

In this paper, we study a new rheological model (a modification of the well-known Pokrovskii–Vinogradov model) which is shown by computational experiments to take into account the nonlinear effects occurring during melt flows and polymer solutions in regions with complex boundary geometry. For the case where the main solution is an analogue of the Poiseuille flow in an infinite flat channel (viscoelastic polymer fluid considered), an asymptotic formula is obtained for the distribution of points of the spectrum of the linear problem. It is shown that small perturbations have the additional property of periodicity in the variable that runs along the axis of the channel.

The airflow and temperature distribution in a heated tunnel greenhouse in the presence of a row of tomato plants owing to heat dissipation from heating pipes is numerically studied with the use of the Fluent-CFD software. The fully turbulent airflow in the greenhouse induced by buoyancy forces is modeled by using the k–ε model. The radiative heat transfer is taken into account by using the model of discrete ordinates. Two types of boundary conditions expressing heat losses at the greenhouse cover are treated: pure convection and convection combined with thermal radiation.

A method for designing a pulsed magnetohydrodynamic generator (MHDG) fueled by the combustion products of the modern aluminized plasma-forming Start-2 solid propellant was developed based on experimental and numerical studies of the characteristics and operating modes of the first-generation 500-MW Sakhalin pulsed MHDG fueled by a solid powder propellant (SPP). This paper presents the results of calculation and optimization of the characteristics of the designed pulsed MHDG with a self-excited resistive “iron-free” magnetic system with an electric power of more than 500 MW. The local, integral, and specific energy, weight, and size characteristics of this generator were determined. Stability parameters of supersonic flow during strong magnetohydrodynamic deceleration of the plasma of combustion products and the time of self-excitation of the magnet were determined. The characteristics of the pulsed MHDG were compared with those of MHDGs fueled by the combustion products of the first-generation SPP. It is shown that the obtained energy, mass, and size characteristics of the MHDG fueled by the Start-2 SPP are much superior to those of the pulsed MHDG fueled by the first-generation SPP.

A forced convection flow and heat transfer of a water-based nanofluid with SiO₂ particles with different volume fractions and nanoparticle diameters in corrugated ducts with different shapes are numerically studied. The three-dimensional governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. The effects of the nanoparticle diameter and shape on heat transfer is considered in the Reynolds number range 3000 ⩽ Re ⩽ 5000, and a uniform wall temperature is applied on the walls. The corrugated duct shape is optimized by the maximum performance evaluation criterion.

Experiments on tension and compression of solid samples cut out from a 60-mm thick plate of an Ti–Al–Sn–V alloy at a temperature of 700◦C are used to determine that this alloy possesses small anisotropy and a different resistance to tension and compression under creep. The approximations of the power law of creep are obtained for each series of these experiments and each direction in the plate. Two models based on the transformed space of stresses are used to simulate the torsion of solid samples. The models account for the different resistance to tension and compression under creep. A series of experiments are carried out on the torsion of solid round rods cut out in the normal direction of the plate. It is shown that the computational and experimental results satisfactorily agree.

A model of a physical section that describes stress–strain states in elastic–plastic solids weakened by cracks is proposed. The problem of plane deformation and the stress state of a solid of an infinite size of an arbitrary geometry, weakened by a physical section, is solved. It comes down to a system of two variational equations with respect to displacement fields in the parts of the solid bordering the interaction layer. For a material whose properties are close to those of a D16T alloy, the linear parameter introduced into the crack model is estimated, and the critical conditions of solids with lateral cracks in the case of a normal detachment are determined.

Cylindrical delamination in a multilayered functionally graded circular shaft loaded in torsion is analyzed assuming a nonlinear mechanical behaviour of the material by using the Ramberg–Osgood equation. The shaft is made of an arbitrary number of adhesively bonded concentric layers of different thicknesses and material properties. In each layer, the material is functionally graded in both radial and longitudinal directions. A solution for the strain energy release rate is derived by analyzing the energy balance. The solution is used to perform parametric investigations of the delamination behaviour.

The process of crack growth in parts subjected to hot fluids is studied. The high temperature of the fluid activates the creep and corrosion processes. The hereditary creep theory is used for calculating the stress field. A creep function is introduced to determine the forces acting on the crack at the crack concealment and crack growth stages. The resisting force is calculated by using the Rabotnov method of accumulated small fractures in the crack region. The effect of the corrosive environment is considered in the calculations by using the penetration function. The resultant equations are solved by using the MATLAB software. The effects of the initial crack length and the applied stress on the crack growth curve are investigated.

Relations for the principal values of the damage tensor based on data on the speeds of longitudinal and transverse waves are proposed. The relationship of acoustic anisotropy with the principal values of the damage tensor are established. The distributions of local speeds and damage along the thickness of the specimen are studied. It is shown that damage is localized in a narrow surface layer, with local damage maxima far exceeding the average damage value.