Vol 53, No 2 (2018)

The steady flow arising in a spheroidal cavity with periodically-deformed elastic wall is studied experimentally. It is found that average flows whose intensities and structures depend on the wall oscillation frequency and amplitude can develop in the fluid. The average flow is generated in the Stokes boundary layer whose relative thickness is characterized by the dimensionless frequency of the vibrational action. Flow in the form of a pair of toroidal vortices which occupy the entire cavity volume can be observed over the range of low dimensionless frequencies when the boundary layer thickness is comparable with the characteristic cavity dimension. Increase in the dimensionless frequency (decrease in the relative thickness of the Stokes layers) leads to a displacement of the primary vortices towards the cavity boundary. In this case secondary vortices with opposite swirling are formed in the central part of the cavity above the primary vortices. The further increase in the dimensionless frequency leads to development of the secondary vortices and growth of the flow intensity. The large-scale secondary vortices occupy almost the entire cavity volume over the range of high dimensionless frequencies. The dependences of the regimes of average flows and their intensities on the control dimensionless parameters, the oscillation amplitude and frequency, are found on the basis of the results of the investigation.

Flat plates, both single and in tandem or side by side arrangement, are widely used in many engineering applications. Despite vast investigations of the flow structures and wakes downstream of these bluff bodies, this unsteady phenomenon yet remains a fundamental issue in many industrial applications. This paper reviews the state of the art concerning the flow over flat plates in different arrangements focusing on plates normal to the flow. Turbulent wake regions are discussed for the flat plates in side by side or tandem arrangement. Numerical studies are reviewed with emphasis on the realized turbulent models. The effect of the chosen turbulence model on the prediction of the wake region is discussed.

The intensity of electromagnetic radiation generated by a charged drop oscillating in a uniform electrostatic field is studied within the framework of analytical calculations retaining the terms of the second order of smallness with respect to the ratio of the droplet oscillation amplitude to the droplet radius. It is found that the charge induced in the drop surface oscillations generates a dipole radiation detected in the first-order calculations and a self-charge detected with allowance for the second-order terms only. It is shown that the order of the magnitude of the total intensity of radiation generated by a cloud can be determined from small-droplet radiation. Among two radiation sources, namely, the radiation generated by small droplets oscillating at low modes and the radiation generated by hydrometeors oscillating at high modes, the first plays a dominant role.

A model of laminar flow of a highly concentrated suspension is proposed. The model includes the equation of motion for the mixture as a whole and the transport equation for the particle concentration, taking into account a phase slip velocity. The suspension is treated as a Newtonian fluid with an effective viscosity depending on the local particle concentration. The pressure of the solid phase induced by particle-particle interactions and the hydrodynamic drag force with account of the hindering effect are described using empirical formulas. The partial-slip boundary condition for the mixture velocity on the wall models the formation of a slip layer near the wall. The model is validated against experimental data for rotational Couette flow, a plane-channel flow with neutrally buoyant particles, and a fully developed flow with heavy particles in a horizontal pipe. Based on the comparison with the experimental data, it is shown that the model predicts well the dependence of the pressure difference on the mixture velocity and satisfactorily describes the dependence of the delivered particle concentration on the flow velocity.

The problem of small perturbations of the equilibriumstate of a viscous, heat-conducting fluid in a cylindrical container with a deformable free upper boundary, on which heat exchange with the ambient medium is preassigned, is studied. The mathematical modeling of convection is based on Oberbeck–Boussinesq equations. The spectral problem thus obtained is solved using the tau method. As a result, the dependence of the imaginary part of the complex decrement on the Marangoni number is obtained. In the case of monotonic perturbations the neutral curves are plotted as functions of a geometrical parameter, namely, the cylinder height-to-radius ratio. The dependence of the Marangoni number on the physical parameters of the fluid is also obtained.

The distinctive features of directmethods for contouring axisymmetric noses of bodies in a supersonic flow are discussed. The nose of a body of revolution in a supersonic flow, optimal with respect to the wave drag, includes a forward-looking flat face adjoining through a bend a sloping region of given aspect ratio (length-to-base-radius ratio), which, in turn, adjoins, again through a bend, the main part of the body. The above-mentioned sloping region can have, depending on its length, some additional internal bends. The presence of bends in a contoured configuration can often be undesirable, owing to strength, thermal, or others restrictions. For this reason, in solving the optimal contouring problems by means of direct methods analytical approximations of the unknown contour are often used, which leads to an increase in the drag of the optimized configuration. The degree of the increase in the drag of the nose part of a body of revolution in the cases of the local smoothing of bends in the optimal configuration and the global variation of its shape on the basis of an analytical approximation is investigated. It is shown that an increase in the drag of the nose part of a body of revolution owing its ineffective approximation can be many times greater than the gain due to optimization. The results of calculations are confirmed by the experimental data obtained.

The formulas for the heat fluxes of heavy components and electrons as well as the Stefan–Maxwell relations for the diffusion fluxes in amagnetic field are derived for amulticomponent two-temperature plasma with regard to the higher-order approximations in orthogonal expansions of the component distribution functions in Sonine polynomials. For the complex transport coefficients of heavy components and electrons exact formulas are obtained in the significantly simpler form as compared with the standard procedure of the Chapman–Enskog method with the minimum number of minimum-order matrix inversions.