Том 52, № 4 (2017)

A class of exact solutions is obtained for the magnetohydrodynamic equations with plane waves which describe the solid-body motion of an ideally conducting gas in a given uniform gravitational field. The gas motion is initiated by the impact of a piston which generates a shock wave propagating through the initial equilibrium state with a decreasing density. Propagation of the shock wave across a current sheet is considered within the framework of the results obtained.

A new design of the wave propulsor is presented. In this design the thrust mechanism is due to the interaction between the waves and the ship structure elements rather than to ship’s motions. To verify the possibility of using a rigidly fixed inclined plate as the ship wave propulsor a model catamaran was constructed in the Institute of Mechanics of Moscow State University. The effect of the upwave motion of the ship, whose mean velocity is a nonmonotonic function of the wavelength, is studied. As the plate edge pierces the water surface, the ship starts to move in the opposite direction, that is, downwave. The experimentally observable effects are also revealed in the numerical simulation using the XFlow software package which involves the meshless lattice Boltzmann method. On the basis of the calculated results it is shown that the upwave motion effect is due to a variation in the hydrostatic force component in the case of wave breakdown.

The problems of the control of steady three-dimensional viscous incompressible flows modeling the gas flow in the vicinity of the attachment line on the leading edge of a swept wing are considered. It is assumed that the control is realized by means of the body force action approximating the action of a periodic sequence of plasma actuators mounted perpendicular to the leading edge. The corresponding boundary value problems for the system of Navier–Stokes equations are numerically solved using the Fourier method along the longitudinal coordinate and second-order difference approximation in the vertical coordinate. An important role played by the control-induced pressure gradient is shown.

The convective stability of quasi-equilibriumof a fluid layer formed by two horizontal coaxial cylindrical surfaces which have different temperatures and rotate at the same angular velocity about the axis of symmetry is investigated theoretically and experimentally. Consideration is carried out from the standpoint of thermal vibrational convection caused by the average lifting force generated as a result of vibrations of a nonisothermal fluid with respect to the cavity. The vibrations are induced by an external field. The action of the centrifugal force field is also taken into account. Stability of mechanical quasi-equilibrium with respect to monotonic plane perturbations, which are, as shown experimentally, the most dangerous, is studied within the framework of the linear analysis. The stability boundaries are constructed for layers of various relative thickness in the plane of control parameters, the centrifugal and vibrational Rayleigh numbers. The thresholds of excitation of two-dimensional convective structures obtained experimentally are in good agreement with the theoretical ones.

A complex shape of an external meniscus formed due to the capillary rise of a liquid along a fiber having the ovoidal profile is considered. Within the framework of the asymptotic approach and under the assumption on the complete wetting of the fiber material by the liquid, an analytical solution of the problem is derived. The particular examples of the meniscus configuration are presented in the cases in which the fiber profile has the shape of an ovoid or an ellipse.

Analytical expressions for the heat flux divided by its value at the stagnation point which depend on the geometric parameters invariant with respect to the choice of the coordinate system, as well as expressions depending on the geometry and the pressure on the surface which have a wider applicability range are obtained in the problem of three-dimensional hypersonic flow over blunt bodies at large and moderate Reynolds numbers. These formulas are derived by solving the thin viscous shock layer equations for a perfect gas using the integral method of successive approximations developed by the author. The accuracy and the range of applicability of the analytical solutions are estimated by comparing them with numerical solutions. On the basis of comparisons with numerical solutions for multicomponent chemically nonequilibrium air at altitudes from 90 to 50 km of the spacecraft reentry trajectory in the Earth’s atmosphere it is shown that the formulas obtained can be used for calculations of the heat flux on an ideal catalytic surface of bodies in hypersonic chemically reacting gas flow.