Channel Of Variable Cross Section Research Articles

Numerical simulation of a boiling up fluid flow in the variable cross-section channels

A physical and mathematical model of a boiling-up fluid flow in the variable crosssection channels is proposed. The numerical model is based on the solution of the Navier-Stokes nonstationary equations for compressible fluid by the implicit finite-difference method. We present the results of the numerical modeling for two-phase flow characteristics at the initial stage of the evaporation process and the steady-state quasistationary flow of a two-phase medium.

Stabilization of detonation waves in a supersonic flow

A supersonic flow in a channel of variable cross section is considered in a quasi-one-dimensional approximation in the framework of a model of infinitely thin detonation waves. An analytical method is developed using special coordinates to analyze the conditions for the existence of steady flow behind a detonation wave. On the basis of numerical experiments, it is shown that the detonation wave can be stabilized. A stability analysis of the steady state is performed with respect to small perturbations of heat release. This analysis allows one to make a selection of the emergent flow pattern.

Numerical Study on the Heat Transfer Characteristic in Periodical Variable Cross-Section Channel

The heat transfer characteristic through periodical variable cross-section passage is studied with numerical scheme. The results in multi-period variable cross-section channel show that the heat transfer enhancement can be obtained by forming flow destabilization at large Reynolds number. The parameters include pressure, velocity, temperature in the channel are symmetric about central line at low Reynolds number, then change to asymmetric at high Reynolds number. The variations occur firstly at the downstream near outlet of the channel and move upstream, which could improve the fluid mixing to increase the enhancement of heat transfer in channel.

Numerical Study on the Flow Characteristic in Periodical Variable Cross-Section Channel

The flow characterizations through periodical variable cross-section passage are performed by numerical simulations in the one wavelength passage with periodic inlet and outlet boundary conditions. The flow patterns through the transient method in the passage show the steady characteristic at low Reynolds number, and the unsteady characteristics include either occurrence or development of self-sustained oscillations as the increasing of Reynolds number. As a consequence of these flow characteristics, the fluid mixing between the core flow and vortexes in trough or crest in channel can be improved to increase the heat transfer.

Three-dimensional numerical simulation of viscous liquid flow in channel of variable cross-section using boundary element method

In the present work the three-dimensional flow of a viscous liquid described by Stokes equations is studied in a cylindrical tube and a channel of variable cross-section. A qualitative triangulation of the surface of a channel variable cross-section is constructed. The problem is solved numerically using the boundary element method in two modifications. A comparison of the method modifications for a channel of different radius of a neck, as well as for the Poiseuille flow with an analytical solution. It is found out the critical radius of the channel neck at which the vortices arise.

Initiation of detonation waves in channels of variable cross section filled with liquid with combustible gas bubbles

Special features are investigated of the initiation of detonation waves in chemically active bubble media located in channels of variable cross section. It is found that, depending on the initial volume content of combustible mixture, the detonation in convergent channels may proceed with the emergence of one or two detonation solitons. The possibility of the emergence of a stable detonation wave upon reflection from the channel bottom is demonstrated in channels with closed bottom. Also demonstrated is the possibility of initiation of detonation upon reflection of the wave from the region of “pure” liquid. Depending on the amplitude of initiating wave and of the initial volume content of bubbles, a map of solutions is constructed which illustrates the modes of the process of detonation in the considered channels.

Elastic turbulence under polymer solutions flow in microchannels with variable cross-section

The flow of a dilute solution of a high-molecular polymer in channels of variable cross-section at low Reynolds numbers exhibits elastic turbulence accompanied by an increase of the hydraulic resistance by several times in comparison with water although the viscosity of the solution is only 10-20% higher than the viscosity of water. This phenomenon was studied in models of glass balls by James and McLaren (1978), in channels of variable cross-section by V.N. Kalashnikov (1987). In described experiments the flow field was visualized in the flat and volumetric models of variable cross-section and in the complex channel structure representing the core section of the oil reservoir. An increase of hydraulic resistance was observed in all types of flow at low Reynolds numbers, pulsations in a flow with a frequency of 5-10 Hz were detected. Competent use of elastic turbulence will significantly increase the efficiency of waterflooding during oil production.

Sub- and supercritical horizontal-shear flows in an open channel of variable cross-section

The concepts of sub- and supercritical flows are introduced for the longwave approximation model describing the steady-state horizontal-shear motions of an ideal incompressible fluid with a free boundary in a channel of variable cross-section. Fluid layer flows developed in a local channel contraction or expansion are analyzed. Continuous and discontinuous exact solutions describing different flow regimes are constructed and their properties are studied. Flows with the formation of recirculation zones are considered.

Lagrangian Modeling of the Dynamics of River and Floodplain Flow

A new Lagrangian, dynamic river model is described. The model solves the coupled one-dimensional hydrostatic flow equations separately in a main river channel and in adjacent floodplains using a two-stage predictor-corrector scheme. The lateral interaction between the main channel and floodplains, due to both advective exchange arising from lateral pressure gradients and turbulent exchange due to lateral shear, is included. The Lagrangian moving grid eliminates numerical diffusion and oscillations commonly experienced in Eulerian models, and can accurately simulate wave propagation and nonlinear steepening until wave breaking. The Lagrangian moving grid is dynamically adaptive, providing variable resolution as the moving fluid parcel’s length changes, either because the cross-sectional flow area or the flow depth changes as the wave moves down a channel of variable cross section. The model also allows flows over dry beds and moving boundaries to be handled efficiently. The model was successfully validated...

Nonstationary flow in the model channel of a ramjet engine in pulse-periodic energy supply

A study has been made of the influence of the pulse-periodic supply of energy that is equal to the energy released in the combustion of hydrogen in air on the structure of supersonic flow in a channel of variable cross section, modeling the duct of a ramjet engine. The flow has been modeled on the basis of two-dimensional nonstationary gas-dynamic equations. Different flow regimes have been obtained depending on the configuration of the zones of energy supply and the excess-air coefficients.

Nonstationary flow in a channel with variable cross section under conditions of periodic pulsed energy supply

The effect of a periodic pulsed supply of energy, equal to that of hydrogen combustion in air, on the structure of a supersonic flow in a channel of variable cross section modeling a ramjet tract has been studied. The flow has been numerically simulated based on two-dimensional gasdynamic equations. Various flow regimes are obtained depending on the configuration of energy supply zones and the excess air ratio in the channel.

Modeling of Nonstationary Flow in the Ramjet Channel with a Distributed Pulse-Periodic Energy Supply

A study has been made of the influence of a pulse-periodic supply of energy that is equal to the energy released in combustion of hydrogen in air on the structure of supersonic flow in a channel of variable cross section, which models the ramjet duct. The flow has been modeled based on two-dimensional nonstationary gas-dynamics equations. Different regimes of flow depending on the configuration of the zones of energy supply and the excess-air coefficient have been obtained.

Nonlinear and curvature effects on peristaltic flow of a viscous fluid in an asymmetric channel

The flow of an incompressible viscous fluid driven by the travelling waves along the boundaries of an asymmetric channel is studied when inertia and streamline curvature effects are not negligible. The channel asymmetry is produced by choosing the wave train on the walls to have different amplitudes and phases. An asymptotic solution is obtained to second order in δ, a ratio of channel width to the wavelength, giving the curvature effects. A domain transformation is used to transform the channel of variable cross section to a uniform cross section, and this facilitates in easy way of finding closed form solutions at higher orders. The relation connecting the pressure gradient and time rate of flux is a cubic leading to non-uniqueness of flux. A uniqueness criterion is derived which restricts the parameters to get a unique flux for a prescribed pressure gradient. The effects of inertia and curvature on pumping, trapping and shear stress are discussed for symmetric and asymmetric channels and compared with the existing results in the literature. Even under a favorable pressure gradient the possibility of fluid flow in a direction opposite to the direction of the waves propagating on the walls is detected as in the case of some non–Newtonian fluids. It is noticed that the effects of Reynolds number and asymmetry may play an important role in producing mixing. Another interesting observation is that the shear stress distribution on the walls vanishes at some points and this will not indicate any flow separation.

The effect of a diaphragm on the vortex thermoinsulation of arc in a plasmatron channel

The pattern of gas (argon) flow and heating in a diaphragmed plasmatron channel is calculated within the framework of an equilibrium magnetogasdynamic model, depending on the diaphragm position and hole size and on the gas flow rate and twist momentum. Special features of the arc characteristics in a channel of variable cross section are established for streams with and without twist.

Effect of the Temperature Drop between the Isothermic Walls of a Channel on the Structure of Supersonic Flow and on the Aerodynamic Properties

The results of numerical analysis of the two-dimensional Navier–Stokes equations are used to investigate a supersonic flow of a perfect gas in a symmetric plane channel of variable cross section at the Mach number of M∞= 4 at the inlet for the Reynolds numbers in the range Re = 103–106. The top and bottom channel walls are assumed to be isothermic with different values of the temperature factor. It is shown that the asymmetry of the boundary conditions for temperature leads to the asymmetry of the entire flow field.

Statics of magnetic fluid drop in channels of various forms

A static equilibrium of the magnetic fluid drop with a constant magnet inside the channels of different form: cylindrical rectilinear and curvilinear, in the channels of variable cross section is studied in this work.

Channel shape optimization of electromagnetic pumps

Channels of variable cross section are used to improve the efficiency of electromagnetic pumps. The optimum channel shape is derived analytically and is then tested with a finite element code. The performances are compared with those of standard pumps. >

Self-sustaining thermoconvective flows in the absence of external force fields

It is shown, analytically and numerically, that if there are no external force fields and the hydraulic resistance is low, sustained thermoconvective subsonic flows may exist in a closed channel of variable cross section, in the wider part of which the medium is heated while in the narrower part it is cooled. The flow parameters depend on the equation of state of the medium, the channel geometry and the amount of heat transferred by the flow from the heated to the cooled part. Steady thermoconvective flows exist up to a certain critical value of the thermal power transported by the flow. The relation between the results obtained and the mechanism by which the motion of the medium is sustained in natural convection is discussed.

An efficient numerical scheme for the two-dimensional shallow water equations using arithmetic averaging

A finite difference scheme based on flux difference splitting is presented for the solution of the two-dimensional shallow water equations of ideal fluid flow. A linearised problem, analogous to that of Riemann for gas dynamics is defined, and a scheme, based on numerical characteristic decomposition is presented for obtaining approximate solutions to the linearised problem, and incorporates the technique of operator splitting. An average of the flow variables across the interface between cells is required, and this average is chosen to be the arithmetic mean for computational efficiency leading to arithmetic averaging. This is in contrast to usual ‘square root’ averages found in this type of Riemann solver, where the computational expense can be prohibitive. The method of upwind differencing is used for the resulting scalar problems, together with a flux limiter for obtaining a second order scheme which avoids nonphysical, spurious oscillations. An extension to the two-dimensional equations with source terms is included. The scheme is applied to the one-dimensional problems of a breaking dam and reflection of a bore, and in each case the approximate solution is compared to the exact solution of ideal fluid flow. The scheme is also applied to a problem of stationary bore generation in a channel of variable cross-section. Finally, the scheme is applied to two other dam-break problems, this time in two dimensions with one having cylindrical symmetry. Each approximate solution compares well with those given by other authors.

Reflection from a vertical wall of a tsunami propagating in a channel of variable cross section: Golin'ko, V.I. and V.I. Malyzhenkova, 1988. Izv. Atmos. Odean Phys. (a translation of Fiz. Atmos. Okeana), 24(11):871–875, Gor'kiy Polytechnic Inst., USSR

Reflection from a vertical wall of a tsunami propagating in a channel of variable cross section: Golin'ko, V.I. and V.I. Malyzhenkova, 1988. Izv. Atmos. Odean Phys. (a translation of Fiz. Atmos. Okeana), 24(11):871–875, Gor'kiy Polytechnic Inst., USSR