Vol 52, No 1 (2017)

Amethod of constructing the model of ideal incompressible unbounded flow past an axisymmetric tube is developed; the tube shape and dimensions are determined in the process of the problem solution. The problem is solved using the method of spatial annular sources and sinks. It is shown that under certain conditions the resulting flow corresponds to that past a round finite-length tube, whose wall has a finite thickness. It is established that near the tunnel entry the flow is considerably restructured.

The piston effect (adiabatic heating or cooling) is investigated numerically for a fluid with parameters in the neighborhood of the thermodynamic critical point. The fluid represents a plane layer on one of whose boundaries a jump in temperature takes place. The temperature of the medium is higher than the critical temperature and the mean density is equal to the critical density. The mathematical model includes the Navier–Stokes and energy equations for a heat-conducting compressible gas and the Van der Waals equation of state. The characteristics of the linear piston effect (properties of fluid are almost invariable) are compared the analytic data. The features of the nonlinear piston effect accompanied by significant variation in the physical properties of the medium are investigated.

The onset of convection in a porous rectangle is analyzed with account for the anisotropy of the thermal parameters and the permeability. For the Darcy–Boussinesq equations the conditions under which the problem pertains to the class of cosymmetric systems are established and explicit formulas for the critical Rayleigh numbers corresponding to the loss of stability of the mechanical equilibrium are derived. The critical numbers and the branching stationary convection regimes are calculated using a finite difference method conserving the problem cosymmetry.

The amplitudemethod of prediction of laminar-turbulent transition on a swept-wing initiated by the simultaneous action of free-stream turbulence and surface roughness is developed. Generation of growing intrinsic perturbations in the boundary layer is described by the mechanism of distributed generation, i.e., an external perturbation generates an instability mode with the same wavelength and frequency. Generation occurs in a small neighborhood of the neutral point at which the parameters of an external perturbation and the instability modes coincide. The development of proper perturbations in the boundary layer is described by the nonlinear method of parabolized stability equations (PSE). The criterion of laminar-turbulent transition is the combined amplitude. i.e., transition begins at a point at which the sum of amplitudes of steady and traveling modes reaches a critical value.

A steady-state axisymmetric model of transport and transition into a plastic state of a permeable elastic body carried by an incompressible power-law fluid in a vertical pipe flow is constructed. Possible flow regimes are found and the threshold values of the parameters responsible for the change of a regime are determined. Semi-analytical expressions for the fluid velocity distribution in the annulus, the pressure difference, and the steady-state velocity of the body are obtained. The conditions of the transition of the body into a plastic state are studied depending on the governing parameters of the problem.

The effect of channel inclination on the variation in the wall shear stress and the heat transfer in a two-phase bubbly flow in a rectangular channel is experimentally and numerically investigated. The wall friction was measured using the electrodiffusion method and the temperature was measured by tiny platinum resistance thermometers. The model is based on the system of RANS equations with account for the back influence of the bubbles on the flow characteristics. Flow turbulence is calculated according to the model of transport of the Reynolds stress tensor components. It is shown that in the gas-liquid flow the angle of the channel inclination to the horizon can have a considerable effect on the friction and the heat transfer. The greatest friction and heat transfer values correspond to the angles of channel inclination ranging from 30 to 50∘. In the inclined two-phase bubbly flow the shear stress enhancement on the wall amounts to 30% and that of the heat transfer to 15%. A friction and heat transfer reduction to 10 and 25%, respectively, is noticed in near-horizontal flows.

The dynamic relations on the phase interface are derived in the isothermal approximation for liquids in which the dependence of the surface energy on the mass flux across the phase interface must be taken into account. The criterion of stability of subsonic phase-transition fronts with plane waves with respect to small perturbations is determined. The dependence of the surface tension on the mass flux is calculated for the well-known exact solution to the problem of the structure of isothermal phase transition within the framework of the generalized van der Waals model.

The concept of the local similarity of nonequilibrium boundary layers in high-enthalpy gas flows past blunt bodies is briefly described. The technical possibilities of the VGU-4 induction high-frequency plasmatron in modeling the aerodynamic heating of the hypothetical Pre-X (CNES) spacecraft in the vicinity of the stagnation point of a high-enthalpy air flow are presented. The engineering approach to quantitatively reproduce the thermochemical effect of a dissociated air flow on the vehicle surface in the high-heat region of the terrestrial entry trajectory is developed. In this approach the full-scale values of the total enthalpy, the stagnation pressure, and the velocity gradient at the stagnation point near the surface are reproduced in the experiment. The effective coefficients of O and N atom recombination on a silicone carbide (SiC) surface are determined under the conditions similar with those of the peak heating of the Pre-X vehicle surface in the vicinity of the flow stagnation point.