Showing papers in "Fluid Dynamics in 2017"
TL;DR: In this article, the stability of two-layer flows with account of evaporation at the thermocapillary interface is studied under the condition of a fixed gas flow rate.
Abstract: The problem of stability of two-layer (fluid-gas) flows with account of evaporation at the thermocapillary interface is studied under the condition of a fixed gas flow rate. In the upper gas-vapor layer, the Dufour effect is taken into account. A novel exact solution of the Navier–Stokes equations in the Boussinesq approximation is constructed. The effects of longitudinal temperature gradients, gravity, thicknesses of the gas and fluid layers, and the gas flow rate on the flow structure, the onset of recirculated flows near the interface, the evaporation rate, and the properties of characteristic disturbances are investigated.
16 citations
TL;DR: In this article, a model of deep-bed filtration of a two-component suspension through a porous medium with formation of two types of the deposit which have different structures and properties is constructed.
Abstract: A model of deep-bed filtration of a two-component suspension through a porous medium with formation of two types of the deposit which have different structures and properties is constructed. The influence of the parameters of fluid and particle flux densities which determine mass transfer between different components of the suspension and deposits on the filtration characteristics and properties of the resulting deposits is estimated on the basis of numerical experiments for the suspensions with contrast particle fractions.
14 citations
TL;DR: In this paper, the spectral stability of the plane phase transition interface is investigated in the presence of capillary forces exerted on the phase transition front in the wettable medium and it is shown that the plane front can be destabilized on the mode with both infinite and zero wavenumbers (short-and long-wave instabilities).
Abstract: The stability of vertical flows through a horizontally extended two-dimensional region of a porous medium is considered in the case of presence of a phase transition front. It is shown that the plane steady-state phase transition front may have several steady-state positions in the wettable porous medium and the necessary condition of their existence is obtained. The spectral stability of the plane phase transition interface is investigated. It is found that in the presence of capillary forces exerted on the phase transition front in the wettable medium the plane front can be destabilized on the mode with both infinite and zero wavenumbers (short- and long-wave instabilities); the short-wave instability can then exist even in the case of the sole steady-state position of the front.
14 citations
TL;DR: In this paper, the stability of a phase transition interface which separates the soil regions saturated with water and humid air, respectively, is investigated, where the humid air region contacting with the atmosphere is assumed to be located above the water-saturated region.
Abstract: The stability of a phase transition interface which separates the soil regions saturated with water and humid air, respectively, is investigated. The humid air region contacting with the atmosphere is assumed to be located above the water-saturated region. Water flows through the porous medium in the lower region, while diffuse vapor transfer is implemented in the upper region. Two cases corresponding to water evaporation and vapor condensation are considered. In the first case water flows out from the porous aquifer, evaporates, and comes out into the atmosphere. In the second case, during condensation, the atmospheric moisture saturates soil. The problem is solved in the steady-state case. The investigation of linear stability carried out by means of the normal mode method shows that the evaporation surface can be unstable in both nonwettable and wettable soils in the presence of the capillary pressure gradient. Depending on the parameters, the condensation surface can be unstable also in the neutral medium.
13 citations
TL;DR: In this paper, exact solutions with plane and cylindrical waves are obtained for one-dimensional problems of injection of a suspension into a porous reservoir when lagging of the suspended particles behind the carrier fluid is taken into account in the case of large change in the porosity.
Abstract: Exact solutions with plane and cylindricalwaves are obtained for one-dimensional problems of injection of a suspension into a porous reservoir when lagging of the suspended particles behind the carrier fluid is taken into account in the case of large change in the porosity. It is shown that taking lagging of the particles behind the fluid into account can lead to slowing-down the motion of jump in concentration. This is in agreement with the results of a series of experiments. It is also noted that, in principle, models in which the particles pass in average ahead of the carrier fluid are possible in the problems of deep bed filtration.
12 citations
TL;DR: In this article, a system of exact integro-differential equations solved relative to the derivatives with respect to time is derived and the equivalent system of equations is obtained in the Dyachenko variables.
Abstract: Waves in deep water with constant vorticity in the region bounded by the free surface and the infinitely deep plane bottom are considered. Using the conformal variables and the conformal transform technique, a system of exact integro-differential equations solved relative to the derivatives with respect to time is derived and the equivalent system of equations is obtained in the Dyachenko variables. The efficiency of using the obtained system in the Dyachenko variables for investigating surface wave dynamics on the current of infinite depth with constant vorticity is demonstrated with reference to numerical experiments.
11 citations
TL;DR: In this article, the aerodynamic heating of a pre-X spacecraft in the vicinity of the stagnation point of a high-enthalpy air flow was modeled using the VGU-4 induction high-frequency plasmatron.
Abstract: 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.
11 citations
TL;DR: In this paper, 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.
Abstract: 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.
10 citations
TL;DR: In this article, the authors considered the problem of acoustic wave reflection and transmission through a multilayer medium containing a bubbly fluid layer and calculated the wave reflection coefficients and compared with the experimental data.
Abstract: The problem of acoustic wave reflection and transmission through a multilayer medium containing a bubbly fluid layer is considered. For the water-water with air bubbles-water model the wave reflection and transmission coefficients are calculated and compared with the experimental data. The problem parameters, at which these coefficients take extremum values, are determined. The influence of vapor within the bubbles on the acoustic wave transmission through a layer of a fluid with the vapor-gas bubbles is shown.
10 citations
TL;DR: In this paper, the results of direct numerical simulation of turbulent flows of non-Newtonian pseudoplastic fluids in a straight pipe are presented for steady turbulent flows at the Reynolds numbers of 104 and 2×104.
Abstract: The results of direct numerical simulation of turbulent flows of non-Newtonian pseudoplastic fluids in a straight pipe are presented. The data on the distributions of the turbulent stress tensor components and the shear stress and turbulent kinetic energy balances are obtained for steady turbulent flows at the Reynolds numbers of 104 and 2×104. As distinct from Newtonian fluid flows, the viscous shear stresses turn out to be significant even far from the wall. In power-law fluid flows the mechanism of the energy transport from axial to transverse component fluctuations is suppressed. It is shown that with decrease in the fluid index the turbulent transfer of the momentum and the velocity fluctuations between the wall layer and the flow core reduces, while the turbulent energy flux toward the wall increases. The earlier-proposed models for the average viscosity and the non-Newtonian one-point correlations are in good agreement with the data of direct numerical simulation.
9 citations
TL;DR: Arational asymptotic theory is proposed in this paper, which describes the turbulent dynamic and thermal boundary layer on a flat plate under zero pressure gradient, where the flow depends on a finite number of governing parameters and algebraic closure conditions relating the turbulent shear stress and heat flux with the gradients of the averaged velocity and temperature.
Abstract: Arational asymptotic theory is proposed,which describes the turbulent dynamic and thermal boundary layer on a flat plate under zero pressure gradient. The fact that the flow depends on a finite number of governing parameters makes it possible to formulate algebraic closure conditions relating the turbulent shear stress and heat flux with the gradients of the averaged velocity and temperature. As a result of constructing an exact asymptotic solution of the boundary layer equations, the known laws of the wall for velocity and temperature, the velocity and temperature defect laws, and the expressions for the skin friction coefficient, Stanton number, and Reynolds analogy factor are obtained. The latter makes it possible to give two new formulations of the temperature defect law, one of which is identical to the velocity defect law and contains neither the Stanton number nor the turbulent Prandtl number, and the second formulation does not contain the skin friction coefficient. The heat transfer law is first obtained in the form of a universal functional relationship between three parameters: the Stanton number, the Reynolds number, and the molecular Prandtl number. The conclusions of the theory agree well with the known experimental data.
TL;DR: In this paper, the effect of a deflector on the aerodynamic and acoustic characteristics of turbulent flow in a cavity is numerically modeled using the immersed boundary method, and the adequacy of the computation method is checked against some similar problems for which there are plausible experimental data.
Abstract: The effect of a deflector on the aerodynamic and acoustic characteristics of turbulent flow in a cavity is numerically modeled. The computation method working on unstructured grids is described. The immersed boundary method is applied to model the deflector. The adequacy of the computation method is checked against some similar problems for which there are plausible experimental data. The results of the calculations of turbulent flow around deflectors of different shape are presented and their influence on the flow structure is analyzed. The results of the large-scale calculations of flow near a cavity are also considered in the presence and the absence of a deflector near the leading edge. On the basis of the numerical data obtained the deflector effect on the aerodynamic and acoustic characteristics of cavity flow is analyzed, including the effect on the acoustical loads on the cavity surface.
TL;DR: In this article, a technique of controlling the flow past the airfoil of a civil aircraft wing is proposed, which consists in blowing a jet tangent to the upper surface of the air foil from a small size slot nozzle.
Abstract: Flow past the airfoil of a civil aircraft wing is numerically modeled in the transonic buffeting regimes. The characteristics of unsteady self-oscillations of the shock on the upper surface of the airfoil are studied. To suppress them a technique of controlling the flow is proposed. It consists in blowing a jet tangent to the upper surface of the airfoil from a small-size slot nozzle. The calculations are carried out within the framework of the unsteady Reynolds equations.
TL;DR: In this paper, the drop material is concentrated in the form of thin fibers which form a regular streaky or netlike pattern in which triangular, quadrangular, and pentagonal cells are expressed.
Abstract: Macrophotography and high-speed videofilming are used to investigate the material transfer in a falling drop upon collision with the surface of a fluid at rest. In the experiments the drops of colored water, milk, mineral oil, and seed oil fell in pure or colored water. Emphasis was placed on recording the pattern of the drop material spreading over the surface of the receiving fluid. On the continuous surface of the primary cavity and the crown the drop material is concentrated in the form of thin fibers which form a regular streaky or netlike pattern in which triangular, quadrangular, and pentagonal cells are expressed. The cell rows are ordered in the form of layers on the lateral walls and the bottom of the cavity. The fiber dimensions and the degree of their expressiveness vary in the process of flow evolution. The upper row of structures on the crown surface is formed by vertical fibers.
TL;DR: In this article, an impermeable layer saturated with a hydrate-icemixture can be formed in reservoirs with initial positive temperature, and the conditions of existence of such a layer in a reservoir with high hydrate content are investigated.
Abstract: The problem of decomposition of methane hydrate coexisting with water in a highpermeability reservoir is considered. The asymptotic solution is obtained for the decomposition regime in the negative temperature domain. Energy estimates presented show that an impermeable layer saturated with a hydrate-icemixture can be formed in reservoirs with initial positive temperature. The mathematical model of the process of hydrate decomposition is formulated under the assumption on the presence of such a layer in a high-permeability reservoir. In this case the problem is reduced to a purely thermal problem with two unknown moving boundaries. The water-ice phase transition takes place on the leading boundary, while hydrate dissociates at negative temperatures on the slower boundary. The conditions of existence of the layer saturated with a hydrate-ice mixture which is implemented in reservoirs with the high hydrate content are investigated.
TL;DR: In this paper, the problem of the radiative gasdynamics of the Apollo-4 command module superorbital entry in the dense terrestrial atmosphere is numerically solved in the two-dimensional formulation of flow past an aerodynamic nose shield on the entry velocity range V∞ = 10.7−5.75 km/s and the altitude range H = 91.5−35.0 km.
Abstract: The problem of the radiative gasdynamics of the Apollo-4 command module superorbital entry in the dense terrestrial atmosphere is numerically solved in the two-dimensional formulation of flow past an aerodynamic nose shield on the entry velocity range V∞ = 10.7−5.75 km/s and the altitude range H = 91.5−35.0 km. The specific regions of the trajectory with strongly nonequilibrium flow in the shock layer, the most high-heat areas of the trajectory, and the regions with strong radiative-gasdynamic interaction in a relatively dense and strongly rarefied oncoming flow are highlighted. The density distributions of the convective and radiative heat fluxes over the body surface are obtained. The spectral composition of the thermal radiation is studied. The results of the calculations are compared and found to be in good agreement with the experimental flight data.
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this paper, the interaction between turbulent jets and the ambient medium is studied on the basis of the results of measurements and numerical simulation, and it is shown that the turbulent flow and the swirl give rise to induced ejection flow toward the jet.
Abstract: The interaction between turbulent jets, both swirling and nonswirling, and the ambient medium is studied on the basis of the results of measurements and numerical simulation. It is shown that the turbulent flow and the swirl give rise to induced ejection flow toward the jet. The mechanism of the jet action on the ambient medium is connected with a decrease in the static pressure in the jet, which, in turn, is due to either the flow swirl or the fluctuating flow in the mixing layer, when the static pressure reduces owing to the presence of velocity fluctuations. The former rarefaction mechanism is predominant in swirling jets and the latter predominates in jets without swirling. It is shown that the ambient medium inflow into the jet due to the rarefaction is independent in nature of the mechanism of the lowered pressure generation and that it is the kinetic energy of the jet that is the energy source for the induced flow.
TL;DR: In this paper, a new design of the wave propulsor is presented, which is due to the interaction between the waves and the ship structure elements rather than to ship's motions.
Abstract: 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.
TL;DR: In this article, a mathematical model of flow of a binary salt-water mixture through a porous medium in a wide range of pressure and temperature is developed taking different multiphase thermodynamic equilibria of the mixture into account.
Abstract: The mathematical model of flow of a binary salt-water mixture through a porous medium in a wide range of pressure and temperature is developed taking different multiphase thermodynamic equilibria of the mixture into account. Formation of concentrated brine lenses above a degassing magma chamber is investigated within the framework of the model. The lenses are assumed to be coupled with generation of ore deposits. It is shown that the lens formation is caused by phase transitions of two different types undergoing at different depths in the magmatic fluid rising towards the surface. In the shallow zones salt precipitation on the skeleton of the porous medium in the form of a solid phase leads to clogging of pore space and reduction of the permeability. As a result, the magmatic fluid flow towards the surface is blocked and this facilitates the concentrated brine accumulation in a local zone.
TL;DR: In this article, the axisymmetric gas flow through a reservoir which contains a heterogeneous mixture, namely, gas hydrate, ice (water), and gas, is considered and exact solutions to the corresponding steady-state and quasi-steady-state nonlinear problems are found.
Abstract: Two problems of axisymmetric gas (gas and water) flow through a reservoir which contains a heterogeneous mixture, namely, gas hydrate, ice (water), and gas, are considered. The exact solutions to the corresponding steady-state and quasi-steady-state nonlinear problems are found. The critical diagrams are constructed for various flow regimes. The characteristic distributions of the gas hydrate, ice (water), and gas saturations are shown for various values of the parameters.
TL;DR: In this paper, the stability of an infinite elastic plate in supersonic gas flow is investigated taking into account the presence of the boundary layer formed on the plate surface, and the effect of viscous and temperature disturbances on the behavior of traveling waves is studied at large but finite Reynolds numbers.
Abstract: The stability of an infinite elastic plate in supersonic gas flow is investigated taking into account the presence of the boundary layer formed on the plate surface. The effect of viscous and temperature disturbances of the boundary layer on the behavior of traveling waves is studied at large but finite Reynolds numbers. It is shown that in the case of the small boundary layer thickness viscosity can have both stabilizing and destabilizing effect depending on the phase velocity of disturbance propagation.
TL;DR: In this article, the effect of wall and bottom geometry on the frequency, height, and decay rate of standing surface waves in a tank oscillating in the vertical direction is investigated.
Abstract: The results of laboratory experiments on the estimation of the effect of wall and bottom geometry on the frequency, height, and decay rate of standing surface waves in a tank oscillating in the vertical direction are presented. The effect of one or two semi-cylindrical inserts mounted on the face and rear walls of the tank is considered in detail for the cases of a horizontal bottom and a linear shallow on the bottom. The experimental data are interpreted using a mathematical longwave model based on the method of accelerated convergence.
TL;DR: In this paper, the Darcy-Boussinesq equations were established and explicit formulas for the critical Rayleigh numbers corresponding to the loss of stability of the mechanical equilibrium were derived.
Abstract: 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.
TL;DR: In this article, two layouts of annular self-adjustment nozzles are optimized for the mean thrust in operation in the launch and altitude flight regimes using the classical and genetic approaches.
Abstract: The comparative efficiency of two layouts of self-adjusted annular nozzles operating over a wide flight altitude range is studied. One of the layouts is presented by the so-called spike nozzles (plane or antisymmetric, with a central body) having the property of self-adjustment when operating in different regions of the flight trajectory. The possibility of locating an annular plug nozzle or a conventional round nozzle in the base region of an axisymmetric spike is considered as a possible means for reducing its base losses. Two layouts of annular self-adjusted nozzles (in combination with internal nozzles or without them) are optimized for the mean thrust in operation in the launch and altitude flight regimes using the “classical” and “genetic” approaches. It is shown that optimal annular spike nozzles in combination with internal nozzles do not provide considerable advantages in the thrust compared with purely spiked optimal configurations. At the same time, an effective optimization of spike nozzles with account for the contribution made by the base thrust can ensure a comparatively low level of the losses.
TL;DR: In this article, the laws of electrostatic instability of the surface of a cylindrical volume charged jet moving relative to the ideal incompressible dielectric medium and the stability of bending-deformation capillary waves developed on the surface are investigated analytically.
Abstract: The laws of implementation of electrostatic instability of the surface of a cylindrical volume charged jet of an ideal incompressible dielectric liquid moving relative to the ideal incompressible dielectric medium and the stability of bending-deformation capillary waves developed on the surface are investigated analytically. It is found that there are thresholds for the critical conditions of implementation of the instability with respect to the jet velocity relative to the medium (Weber number) and with respect to the electric space charge (relative to the ratio of the electrostatic pressure on the jet surface to the Laplace pressure). The critical analytic dependence between these dimensionless parameters is found.
TL;DR: In this article, a physically validated approach to the setting of an experiment is presented and the methodological aspects of an analysis of experimental data for establishing the distinctive features of the fuel mixture combustion in variable-cross-section channels are considered.
Abstract: The physically validated approaches to the setting of an experiment are presented and the methodological aspects of an analysis of experimental data for establishing the distinctive features of the fuel mixture combustion in variable-cross-section channels are considered. The special features of determining the fuel combustion efficiency coefficient in subsonic and supersonic flows are considered with account for heat removal into the channel walls. The effect of the fuel combustion efficiency coefficient on the distributions of gasdynamic and thermodynamic parameters along the length of the internal ducts of channels of different configurations is analyzed. The results of the testing of the techniques proposed against an experimental investigation of gaseous hydrogen combustion in high-enthalpy air flows are presented. The results obtained and the mathematical models developed can be used at the stage of computational and experimental investigations of the working process in promising power plants.
TL;DR: In this paper, 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.
Abstract: 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.
TL;DR: In this article, the authors investigated the linear stability of viscous two-dimensional perturbations in the supersonic plane Couette flow of perfect and vibrationally excited gases.
Abstract: The linear stability of viscous two-dimensional perturbations in the supersonic plane Couette flow of perfect and vibrationally excited gases is investigated. In both cases an alternative is considered so that the transport coefficients were taken either constant or dependent on the static flow temperature. The Sutherland model is used to take the temperature dependence of the shear viscosity into account. It is shown that “viscous” stratification increases considerably the flow stability as compared with the case of constant viscosity. At the same time, the simple constant viscosity model conserves all characteristic features of the development of viscous perturbations in the Sutherland model. The dissipation effect of excitation of the vibrational mode is conserved in taking the temperature dependence of the transport coefficients into account. For both models the corresponding increase in the critical Reynolds number is of approximately 12%.
TL;DR: In this article, the results of the experimental investigation of gravitational sedimentation of a consolidated system of solid monodisperse spherical particles in a viscous liquid are represented over wide ranges of the particle number density and the Reynolds and Stokes numbers.
Abstract: The results of the experimental investigation of gravitational sedimentation of a consolidated system of solid monodisperse spherical particles in a viscous liquid are represented over wide ranges of the particle number density and the Reynolds and Stokes numbers. Empirical dependences of the velocity of sedimentation of a particle aggregate and the drag coefficient of a system of particles as functions of the initial volume number density are obtained. The boundary values of the particle number density separating the sedimentation regimes are determined.