Two-phase Flow Coupling Research Articles

Calibration and Experimentation of Discrete Elemental Model Parameters for Wheat Seeds with Different Filled Particle Radii

A Gas–solid two-phase flow coupling simulation is widely used to study the working process of pneumatic seed dischargers. Due to the demand for deterministic particle orbit numerical calculation models, seeds are mostly modeled using the particle aggregation method, where the seed model is formed through particle aggregation bonding without overlapping. The smaller the radius and the more filled ball particles used in this method, the closer they resemble the real morphology of the seed. However, this results in the over-consumption of simulation computational resources and simulation time growth. In this study, we used wheat seeds as the research object, studied the effect of seed models with different filled ball radii on the kinetic response characteristics between the particles, and searched for the optimal number of filled ball particles for the seed model. With the help of three-dimensional scanning and inverse fitting methods to obtain the seed profile, we used different radii (0.2 mm, 0.24 mm, 0.28 mm, 0.32 mm, 0.36 mm, and 0.4 mm) to fill the ball particles, and formed a wheat particle bonding model for a gas–solid coupling simulation. We used a combination of real tests and simulation measurements of bottomless cylinder-lifting and slip-stacking. The interspecies static and dynamic friction factors in seed models with different radii of filled spherical particles were first calibrated using the angle of repose as an index. Then, the parameters were verified using bottomless cylinder lifting and slip stacking tests, which used the coefficient of variation for the simulation test’s angle of repose as an index. Our results show that the smaller the radius of the filled ball, the closer the simulation results were to the real value. Validation was conducted using a gas–solid coupling simulation of an air-blown wheat seed discharger, with the seed filling rate as an index. Our results showed that the simulation length and simulation accuracy were optimal when the radius of the filling particle was 0.32 mm.

Research on diffusion characteristics of liquid jet effected by shock wave in supersonic high-enthalpy crossflow

The diffusion characteristics of liquid jets with phase transition under the action of shock waves in supersonic high-enthalpy crossflow were discussed in this paper. Numerous numerical simulations were carried out in high enthalpy inflow (Tt = 1680 K) under different shock wave intensity and injection parameter conditions. The Euler-Lagrangian method was employed to solve the gas-liquid two-phase flow coupling, and the evaporation, diffusion and mixing processes of kerosene were obtained. By analyzing simulation results, the influence and the mechanism of shock waves on enhanced kerosene mixing were revealed. The results show that increasing the shock wave intensity effectively improves the penetration and mixing of kerosene in general by changing the flow state and evaporation process. The penetration depth can be increased by up to 63.54 % in this paper. To balance the contradiction between total pressure loss and mixing efficiency, it is necessary to select an appropriate shock wave intensity. The enhanced diffusion and mixing process of kerosene by shock waves are related to the injection momentum ratio, evaporation momentum ratio and streamwise vortex intensity. Weakening mainstream momentum while boosting evaporation and vortex intensity effectively strengthens kerosene diffusion and mixing. This research significantly contributes to enhancing the diffusion and mixing of liquid kerosene and improving combustor performance.

Numerical simulation of coated proppant transport and placement in hydraulic fractures based on CFD-DEM

Channel fracturing technology is designed to form fractures supported by non-uniform pillar proppants. Non-cured adhesive resin-coated proppant gradually becomes viscous after immersion and agglomerates during transportation. The pillars are stable after the fracture is closed. They not only maintain a certain compressive strength but also maintain long-term conductivity. Currently, there are few evaluations of coated proppant migration. Based on CFD-DEM method, a two-phase flow coupling model considering the adhesive contact force of coated proppant particles is established to study the cementation characteristics of coated proppant during transportation. The transportation mechanism of coated proppant are revealed by numerical calculation analysis. The results show that different from the conventional proppant, the migration process of the coated proppant is divided into four stages (1) the softening of the proppant contact; (2) the paving of the proppant agglomeration; (3) proppant pillars growth along fracture height; and (4) proppant pillars growth along fracture length. We have completed a preliminary geometric characteristics evaluation of sand bank formed by coated proppant by evaluating the pore volume ratio (the ratio of void volume between pillars to the sand bank volume) under various parameters. This evaluation offers some theoretical guidance for the optimization of channel fracturing proppant injection parameters.

Some Comments on Added Mass Modeling for Tube Bundles Under Two-Phase Cross Flow

Abstract Within the study of fluid-elastic instability in heat exchangers tube banks, a considerable theoretical and experimental effort has been produced for understanding fluid–structure coupling in two-phase flow. This communication discusses the commonly accepted added mass modeling and proposes some ways of further improvement. Notably, it turns out that added mass may be overestimated in a two-phase flow. Taking into account this phenomenon improves the collapsing of flow-induced forces data.

SPH numerical simulation of non-steady sand ripple wind-sand flow structure.

The Smoothed Particle Hydrodynamics (SPH) method is used to numerically simulate the unsteady sand ripple wind-sand flow movement in a small scale. Compared with the traditional grid-based numerical method, the SPH method uses discrete independent particles to represent the solution domain, get rid of the constraints of the computational grid, and completely solve various problems caused by large deformation or distortion of the grid based on the Euler grid method. Because it also includes the Lagrangian dynamics method, it can easily track the trajectory of any single particle, so the SPH method has unique advantages when dealing with the two-phase flow coupling of wind and sand. This paper expounds the theoretical basis and calculation method of SPH method and focuses on the design idea of applying the core factors in the SPH formula to the numerical simulation program. By discretizing the SPH numerical model of the sand ripple wind-sand two-phase flow, the temporal and spatial changes of the sand particle group on the slope surface during the wind-sand movement are simulated. The formation and development process of macro-wind-sand flow and the saltation law of micro-typical particles are analyzed, which are consistent with the existing wind tunnel experiment results, and the accuracy of SPH numerical simulation method is verified. The results show that the calculation accuracy of this method is high, and it provides a scientific theoretical basis for our further research and prevention of sand damage.

Study on tribocharging of CaCO3 particles based on CFD-DEM gas-solid two-phase flow coupling

Unsuccessful prediction of particle tribocharging in tribocharger is partly due to the complexity of tribocharging process. In this work, computational fluid dynamics-discrete element method (CFD-DEM) modeling approach has been used to investigate particle charge in a cyclone tribocharger. Then particle image velocimetry (PIV) method is used to calculate the particle charge-to-mass ratio. The CaCO3 particle charge in a cyclone tribocharger is simulated and predicted under different gas velocities, particle sizes and moving distances. The simulation results carry out the quantitative and qualitative relationship between different parameters. At the same time, the charge-to-mass ratio between the particle simulation and the experimental results under different gas velocities is compared, and the results are all in the magnitude of 10−4. Experimental results in terms of particle charge-to-mass ratio are thus obtained. The CFD-DEM model is verified by comparison with the experimental results

Structure Optimization of Rib Drill Pipe Based on Gas-Solid Coupling and Orthogonal Experiment

At present, drilling rig is a common equipment for controlling gas outburst generated in underground coal mine, and rib drill pipe is an important component of drilling rig. Due to the insufficiency of slag discharge capacity, pipe-sticking accidents often occur during the drilling process, which greatly reduces the effect of gas control. In order to improve the capacity of slag discharge of rib drill pipe, the mechanism of slag removal was analyzed, and the process of slag discharge was simulated as a gas-solid two-phase flow coupling process. Utilizing the computational fluid dynamics method, the process of slag discharge was simulated on the Edem-Fluent cosimulation platform. The structural parameters of the drill pipe affecting the capacity of slag discharge were derived. Based on the analysis results, the structural parameters of rib drill pipe were optimized by orthogonal experiment method. The global optimal results were obtained as follows: its pitch, blade height, and blade width are 120 mm, 3 mm, and 15 mm, respectively. Therefore, the results of slag discharge experiment on the optimum structure of rig drill pipe show that the slag discharge efficiency is increased by 11.38%, which effectively resolves the pipe-sticking problem.

Two-phase SPH model based on an improved Riemann solver for water entry problems

There are challenges in simulating two-phase flows with large density ratios using traditional SPH. Taking full advantages of Riemann solver in dealing with contact discontinuity problems and combining two-phase flow SPH method with Riemann solver, a new model of two-phase flow coupling with structure based on an improved Riemann solver is described for the water entry problems with the effect of air. The flow momentum equation of the Riemann form is improved to decrease the Riemann dissipation and simulate the two-phase flows with different viscosity ratios. One-sided Riemann problem considering the free-slip and no-slip conditions at a wall is used to deal with the fluid-body interaction. A switch-function-based Riemann solver dissipation is used to improve the instability of interface owing to the strong impact. In order to test the accuracy of the model in fluid-structure coupling problems, five cases, including dam break, sinking of a rectangle body, water entry of a wedge, flat plate slamming on water and water entry of a catamaran, are numerically simulated. The agreements between the present results and other reference results demonstrate that the proposed method is robust and stable to simulate the water entry problems with the air.

Study on turbulence control method and surface quality analysis of softness abrasive flow machining

To improve mould structural surface quality, the softness abrasive flow (SAF) finishing method is proposed. By setting restrained component to the mould surface, restrained flow passage can be set up. In the flow passage, micro force and quantity cutting for the tiny scale structural surface is realised by using the turbulence wall effect of SAF. Dynamical model of SAF is established based on liquid-solid two-phase flow coupling theory. Semi-annular flow passage is taken as the research object, and turbulent parameters with different flow passages are analysed by using standard k-e turbulent model and discrete phase model (DPM), which is used for describing the influence to turbulent state caused by different boundary conditions, meanwhile, the optimisation design of finishing parameters can be obtained. Finishing platform is constructed, and finishing experiment results show that with the SAF method, the roughness machined is less than Ra 62 nm.

The Numerical Simulation of the Single Abrasive Motion Law in the Environment of Structural Surface

As far as the controllability of turbulence flow field surface effect of the soft abrasive flow was concerned, to begin with the analysis of the motion of the particle in the flow field, the paper studied the motion law of particle in the flow field, especially in the boundary layer. Based on the fluid-solid two-phase flow coupling style, it established the single particle dynamics model. Then it established the realizable k-ε model, in the light of the numerical simulation of turbulent flow. With the adoption of the computational method of SIMPLEC, it asked for the velocity and the pressure of fluid in the U-shaped flow passage, the velocity and the motion law of particles with different granularities and velocity, in the boundary layer. Experimentation results tell us that the original velocity plays a leading role in the motion trajectory of particles. The diameter influenced the particles motion trajectory in some degree.

Structured Surface Softness Abrasive Flow Precision Finish Machining and Its Abrasive Flow Dynamic Numerical Analysis

A new mould structural surface no-tool precision finish machining method based on soft abrasive flow is brought forward. By installing constraint module at nearby the structured surface to be machined, the surface becomes a configurable restrained flow channel (RFC). Micro force and micro amount cutting for RFC is realized by using the turbulence wall effect of liquid-solid two-phase soft abrasive flow in RFC. It will overcome the difficulty of the polishing tool to contact the structured surface and accomplish the no-tool precision machining of the structured surface. Dynamical model of soft abrasive flow in RFC oriented to structured surface precision machining is established on the basis of liquid-solid two-phase flow coupling theory. Choosing corresponding conjunction parameters of different constraint modules, annular constriant flow channel is taken as the research object, and its pressure/velocity distribution and turbulent kinetic energy are analyzed by using standard k-e turbulent model and discrete phase model. The influence of relative variation of inlet/outlet conditions on the turbulent flow pattern can be inspected through the numerical analysis, thus providing a theoretical tool for the research of the basic law of soft abrasive flow form control and the abrasive flow characteristics.

Theoretical Analysis of Viscous Coupling in Two-phase Flow through Porous Media

Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept. The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression, Xϕ 2, was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2.

Experimental Testing of Interfacial Coupling in Two-Phase Flow in Porous Media

Two-phase flow through natural porous media is affected by the interfacial coupling that takes place across the interfaces located in a porous medium. Such coupling may be of two types: viscous and capillary. In this study, defining equations for the capillary and viscous coupling parameters have been constructed. Moreover, these equations, together with a modified form of Kalaydjian's transport equations, have been used to analyze interfacial coupling in two-phase flow through porous media. On the basis of the analysis carried out, it is argued that interfacial coupling has no effect on steady-state, cocurrent flow, and only a small effect on unsteady-state, cocurrent flow. Moreover, it is suggested that interfacial coupling has a significant effect on steady-state, countercurrent flow. Two methods were used to test the theory. In the first method, data from steady-state, cocurrent, and countercurrent experiments were used to show that experimentally determined values of the capillary coupling parameters were in good agreement with those predicted theoretically. Because of experimental problems, it was not possible to determine experimentally, when using the first method, the magnitude of the viscous coupling parameters. In the second method, data from steady-state and unsteady-state, cocurrent flow experiments, using fluids having different viscosity ratios, and porous media having different grain-size distributions, were used to test the theory. Because of a lack of sufficient precision in the measured data, it was not possible to make definitive statements with respect to the adequacy of the theory, or the possible impact of viscosity ratio and grain-size distribution on capillary coupling. Moreover, for the same reason, it was not possible to obtain reliable estimates of the magnitude of the capillary coupling parameters. Because the second method is based on the assumption that viscous coupling is negligible, it was not possible to use this method to determine experimentally the magnitude of the viscous coupling parameters.

Positive Effect of Flow Velocity on Gas-Condensate Relative Permeability: Network Modelling and Comparison with Experimental Results

Positive velocity dependency of relative permeability of gas–condensate systems, which has been observed in many different core experiments, is now well acknowledged. The above behaviour, which is due to two-phase flow coupling in condensing systems at low interfacial tension (IFT) conditions, was simulated using a 3D pore network model. The steady-dynamic bond network model developed for this purpose was also equipped with a novel anchoring technique, which was based on the equivalent hydraulic length concept adopted from fluid flow through pipes. The available rock data on the co-ordination number, capillary pressure, absolute permeability, porosity and one set of measured relative permeability curves were utilised to anchor the capillary, volumetric and flow characteristics of the constructed network model to those properties of the real core sample. Then the model was used to predict the effective permeability values at other IFT and velocity levels. There is a reasonable quantitative agreement between the predicted and measured relative permeability values affected by the coupling rate effect.

The Physical Origin of Interfacial Coupling in Two-Phase Flow through Porous Media

Recently developed transport equations for two-phase flow through porous media usually have a second term that has been included to account properly for interfacial coupling between the two flowing phases. The source and magnitude of such coupling is not well understood. In this study, a partition concept has been introduced into Kalaydjian's transport equations to construct modified transport equations that enable a better understanding of the role of interfacial coupling in two-phase flow through natural porous media. Using these equations, it is demonstrated that, in natural porous media, the physical origin of interfacial coupling is the capillarity of the porous medium, and not interfacial momentum transfer, as is usually assumed. The new equations are also used to show that, under conditions of steady-state flow, the magnitude of mobilities measured in a countercurrent flow experiment is the same as that measured in a cocurrent flow experiment, contrary to what has been reported previously. Moreover, the new equations are used to explicate the mechanism by which a saturation front steepens in an unstabilized displacement, and to show that the rate at which a wetting fluid is imbibed into a porous medium is controlled by the capillary coupling parameter, α. Finally, it is argued that the capillary coupling parameter, α, is dependent, at least in part, on porosity. Because a clear understanding of the role played by interfacial coupling is important to an improved understanding of two-phase flow through porous media, the new transport equations should prove to be effective tools for the study of such flow.

An alternative description of viscous coupling in two-phase flow through porous media

A new formalism is developed to describe the viscous coupling phenomena between two immiscible, flowing fluids in porous media. The formulation is based on the notation of 'two-phase mixture' in which the relative motion between an individual phase and the mixture in porous media can be described by a diffusion equation. The present formulation is derived from Darcy's law with cross-terms without making further approximations. However, the new formulation requires fewer effective parameters to be determined experimentally, thus offering a more viable tool for the study of two-phase flow dynamics with viscous coupling in porous media. Moreover, it is found that no new term appears in the present model in cases with and without viscous coupling; instead, the incorporation of viscous coupling only modifies the effective parameters. It can thus be concluded that viscous coupling does not represent a fundamentally new phenomenon within the framework of the present formulation.

Viscous coupling in two-phase flow in porous media and its effect on relative permeabilities : Ehrlich, R Trans Porous MediaV11, N3, June 1993, P201–218

Viscous coupling in two-phase flow in porous media and its effect on relative permeabilities : Ehrlich, R Trans Porous MediaV11, N3, June 1993, P201–218

Viscous coupling in two-phase flow in porous media and its effect on relative permeabilities

An idealized model of a porous rock consisting of a bundle of capillary tubes whose cross-sections are regular polygons is used to assess the importance of viscous coupling or lubrication during simultaneous oil-water flow. Fluids are nonuniformly distributed over tubes of different characteristic dimension because of the requirements of capillary equilibrium and the effect of interfacial viscosity at oil-water interfaces is considered. With these assumptions, we find that the importance of viscous coupling depends on the rheology of the oil-water interface. Where the interfacial shear viscosity is zero, viscous coupling leading to a dependence of oil relative permeability on oil-water viscosity ratio for viscosity ratios greater than one is important for a range of pore cross-section shapes and pore size distributions. For nonzero interfacial shear viscosity, viscous coupling is reduced. Using values reported in the literature for crude oil-brine systems, we find no viscous coupling.

Added mass effects in fluidized beds: application of the Geurst—Wallis analysis of inertial coupling in two-phase flow

Added mass effects are incorporated into a formulation of the equations of change for fluidization (the particle bed model) using the very simple procedure proposed recently by Wallis ( IMA Workshop Proceedings, in press, 1989) for two-phase flow. Added mass is shown to significantly affect the behaviour of liquid fluidized beds of relatively low density particles. Quantitative predictions of this effect on the velocity of dynamic waves are found to improve agreement with experimental measurements.