Gas-particle Two-phase Flow Research Articles

An Open-Source Code for High-Speed Non-Equilibrium Gas–Solid Flows in OpenFOAM

This paper details the development and verification tests of an open-source code named hy2LPTFoam intended for solving high-speed non-equilibrium gas-particle flows in OpenFOAM. The solver, based on hy2Foam for high-speed non-equilibrium gas flow, integrates multiple particle force models, heat transfer models, the diffusion-based smoothing method, and the MPPIC method. The verification tests incorporate interactions between shock waves and particle curtains with varying particle volume fractions, a JPL nozzle generating a two-phase gas–particle flow, and a Mars entry body with two particle inflow mass fractions. The tests yield good physical agreement with numerical and experimental data from the literature.

Study on particle deposition in pipeline groove from gas–particle two-phase flow

In the process of particle–fluid flow, solid particles are easily deposited in pipes, which leads to collisions and abrasion, especially in pipelines with grooves. Therefore, some structural components are always designed above the groove to improve particle trajectories inside the groove in the pipeline. In the present study, the deposition of particles was analyzed in detail by means of experimental visualization, and Computational Fluid Dynamics and Discrete Element Method model (CFD-DEM) methods were used to investigate the motion and deposition of particles when both grooves and baffles are designed in the pipeline system. Finally, the effect of the baffle width on the deposition of particles in the groove was studied. The results show that the baffle width has a slight effect on the mass of particles deposited in the groove after the number of particles there stabilizes, but when the width of baffle is the same as that of the groove, the time it takes the particles to reach this stable state is shortest.

МЕТОДЫ ПРОЕКТИРОВАНИЯ ПНЕВМАТИЧЕСКИХ СИСТЕМ

In this paper, the parameters of a two-phase heterogeneous gas-particle flow (for example, “airseed”) are shown using the example of mathematical modeling of technological processes of a pneumatic system of a grain seeder. It is proposed to apply the mechanics of two-phase gas-particle flow to the theoretical description of the processes of motion and distribution of solid particles in pneumatic systems. The results of the study establish the possibility of using these methods to analyze and optimize the pneumatic system of grain seeders. Practical and theoretical methods were used to determine the air flow and speed of movement of seeds of various crops in pneumatic systems of grain drills. The values of the seed resistance coefficients necessary for mathematical modeling of the technical processes of the pneumatic system are also presented. The research will make it possible to effectively simulate the operation of the pneumatic system of the sowing complex using the mechanics of two-phase flows and computational fluid dynamics methods.

Loosely coupled analysis strategy for melt-ablation modeling of thermal protection material in supersonic gas-particle two-phase impingement flow

In this study, a two-way fluid-thermal-ablation loosely coupled analysis strategy is used to investigate the melt-ablation process of the copper specimen plate in the scaled ducted launcher. By coupling a discrete-phase model for simulate the supersonic gas-particle two-phase exhaust plume impingement flow field of a small scaled solid propellant rocket and a solidification/melting model for simulate the melt-ablation process of a copper specimen plate, the ablation depth profile of the copper specimen plate at a burn time of 3.6 s is successfully estimated. The numerical model is validated by experimental-scale test which shows that the simulation results using the two-way fluid-thermal-ablation loosely coupled analysis strategy can accurately predict the ablation depth profile of the copper specimen plate.

Dusty Gas Flow past Bodies under Scattering of Rebounded Particles

Two-phase gas-particle flow over a flat plate of finite thickness in a channel at a high subsonic velocity and supersonic transverse flow past a cylinder are considered. The leading edge of the plate is wedge-shaped or represents a smooth bluntness of constant radius. The wedge surface and the front bluntness are specified both smooth and rough. The roughness is modeled by a two-dimensional profile based on an experiment. Spherical particles and a mixture of particles in the form of ellipsoids of revolution, rectangular prisms, prisms with flat-cut vertices, and tetrahedrons are considered. The parameters of each of the forms vary. The impact interaction model proposed earlier and consistent with the experimental data on the coefficients of restitution of the center-of-mass velocity is used to determine the translational and rotational velocities of non-spherical particles after rebound. Along with monosized particles, a dispersed phase with a spread of particles in size is considered. The role of the studied factors of random nature which affect the flow pattern and the dispersed phase parameters is found.

Two Coupled Analysis Strategies for Melt-Ablation Modeling of Thermal Protection Material in Supersonic Gas-Particle Two-Phase Impingement Flow

In this study, two analysis strategies were used to investigate the melt-ablation process of the copper specimen plate in the scaled ducted launcher. The reliability of the simulation results of the two analysis strategies was confirmed by comparing the two-way fluid-thermal-ablation coupled analysis (two-way FTA-CA) strategy with two-way fluid-thermal-ablation loosely coupled analysis (two-way FTA-LCA) strategy. Then, the accuracy of the FTA-LCA strategy was validated by comparing the simulation results of the FTA-LCA strategy and experimental results from the experimental scale test. Finally, the FTA-LCA strategy used in this study can not only estimate the impingement surface heat flux into the copper plate when the inverse heat conduction analysis (IHCA) is not possible, but also provide the analysis solution accuracy and the considerable gain in computational efficiency for predicting the long-duration ablation problem in supersonic gas-particle two-phase exhaust plume impingement flow.

Efficient Focusing of Aerosol Particles in the Microchannel under Reverse External Force: A Numerical Simulation Study.

Focusing aerosol particles efficiently is of great significance for high-precision aerosol jet printing and detection of the airborne target. A new method was proposed herein to achieve the efficient focusing of aerosol particles in the microchannel by using a reverse external force. Considering the slip at the interface between the gas and the aerosol particle, a numerical model of the particle movement in the microchannel was established and simulations were conducted on the gas-particle two-phase flow in the microchannel under the effect of the reverse external force. The results showed that a suitable reverse external force in a similar order of magnitude to the Stokes force can dramatically increase the velocity difference between the particle and the gas, which significantly enhances the Saffman lift force exerted on the aerosol particle. Eventually, the aerosol particle can be efficiently focused at the center of the microchannel in a short channel length. In addition, the influence of the channel geometry, the magnitude, and the direction of the external force on the particle focusing was also studied. This work is of great significance for the precise detection of aerosol particles and the design of nozzles for aerosol jet printing.

CFD–DEM simulation of gas-driven sampling on asteroid regolith: Dependence of collected mass on gas ejection

Asteroids are the remnants of the process by which planets formed from the protoplanetary disk. Laboratory analyses of materials originating from asteroids give us the unique opportunity to reveal the formation history of our Solar System about 4.6 billion years ago. To obtain surface regolith in the low-gravity and vacuum environment, a gas-driven sampling strategy has been proposed, but the relation between the collected mass and the gas ejection remains to be explored, which is important for the development of efficient sampling mechanism designs. In this paper, we simulate the gas-particle two-phase flow in the gas-driven sampling process by using the coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) method. The results show that the sampling process can be divided into three stages according to the mass of particles that are sampled. Initially, the impact ejection of the pressurized gas on the regolith layer dominates, during which the sampling speed increases to a maximum value rapidly. After that, the gas flow transports the ejected particles to the collection chamber. In this stage, the conveyance effect of gas plays a primary role. As grains accumulate near the entrance of the collecting tube, jamming state happens and obstructs the particle flow, making the sampling rate drop to a stable value. By varying the inlet gas velocity, we show that higher gas velocity increases the collected mass rate greatly at the first stage while no significant differences are found after the development of jamming state inside the chamber. The position of the inlets affects the flow field and thus could be used to prevent the unfavorable aggregation of particles near the collecting tube, which facilitates the sampling. The influence of the inlet gas angle is also explored. We find two inward tilting gas inlets could increase the sampling efficiency considerably through striking a balance between ejected mass and ejecting velocity. The results presented in this article are expected to provide important information on the optimal designs of gas-driven sampling devices for future asteroid space mission. • CFD-DEM method is used to study the gas-driven sampling on asteroid regolith. • The impact ejection of pressurized gas and its conveyance effect dominate at different stages. • The gas inlet velocity affects the sampling efficiency only at the initial stage. • The inlet position and angle can be used to prevent the unfavorable jamming of particles.

Deposition of micron-sized inertial particles on flat surfaces: effects of electrostatic forces and surface roughness

Micron-sized particles are prone to deposit on smooth surfaces. A micron-sized particle collision-deposition model including the effects of electrostatic forces, integrated with the factors of particle size, material properties, elastic–plastic deformation, particle charging, surface roughness, and van der Waals forces, is proposed. The effects of the electrostatic forces on the critical deposition velocity, collision duration, and coefficient of restitution (COR), which is the ratio of particle velocity after and before the collision, are investigated for 1–20 μm sand particles colliding with glass, steel, and aluminum alloy surfaces. The results show that the electrostatic forces of sand particles are approximately 106–108 times their gravity and increase the impact duration. Moreover, these forces increase the critical deposition velocity by 2.32–6.89% for the glass surface and decrease the COR by 0.6–3.5% for the three surfaces, while the particle size is below 20 μm and the roughness is 1 nm. The electrostatic forces ranked from the maximum to the minimum are those of the aluminum alloy, steel, and glass surfaces for the same particle size and surface roughness. The developed model can perfect the theory of particle flow and gas-particle two-phase flow.

Experimental and numerical study on the development process and flow characteristics of powder fuel jet in the powder fuel scramjet

The injection process of powder fuel directly affects the scramjet operating performance. This study analyzes gas-particle two-phase flow during powder fuel injection. The macroscopic behavior of powder fuel jets under different injection pressure conditions is characterized using the high-speed shadow imaging technology. Simultaneously, the coupled model of computational fluid dynamics-discrete element method is employed to determine the experimental conditions, and the flow field structure and gas-particle interactions are analyzed. The results show that the development of powder fuel jets mainly occurs in three stages: the low-speed development stage, the high-speed development stage, and the stable stages. A long transition period exists between different stages, and the transition time decreases with increasing injection pressure. In the low-speed development stage, the powder fuel jet initially develops slowly and then develops rapidly. In the high-speed development stage, the jet initially develops rapidly and then develops slowly. The jet in the stable stage is classified into the powder particle, fluidized gas, and free flow regions. The distribution range of the particles decreases with increasing injection pressure. The fluidized gas velocity and drag force curve on the axis experience many fluctuations, and the particle velocity is almost always accelerated. Fluidized gas velocity, drag force, particle velocity, and particle acceleration distance increase with the injection pressure.

Numerical study on the transverse jet flow and mixing characteristics of hydrogen/metal powder fuel in powder fuel scramjet

The powder fuel scramjet is one of the most promising propulsion systems for future hypersonic vehicles. To study the flow mechanism and mixing characteristics of gas-particle two-phase fuel in a supersonic crossflow. In this study, the porosity was introduced into the Navier-Stokes equation, and a program suitable for solving gas-particle two-phase flow in the supersonic flow field was developed. The evolution process of vortex structure, hydrogen/metal powder fuel distribution, jet penetration depth, and mixing efficiency in the single-hole and the double-hole jet flow fields were analyzed. The results show that the particle disturbance reduces the center position of the Mach disk, the height of the barrel shock and jet shear layer, intensifies the Kelvin-Helmholtz instability in the flow field and forms a large number of large-scale coherent structures downstream of the jet. The jet and supersonic crossflow interaction form a large-scale CVP structure for hydrogen fuel. Among them, three pairs of CVP structures (including CVP-B, CVP-C, and CVP-D) appear before and after the downstream of the double-hole jet. CVP-C is the main factor affecting the shape and area of the hydrogen fuel reaction zone. For powder fuel, the penetration depth of fuel is mainly affected by the height of the Mach disk and the shear layer. The higher Mach disk and shear layer position, the greater the velocaity obtained by particles and the higher the penetration kinetic energy. The double-hole injection system has a higher fuel penetration depth and higher mixing efficiency of hydrogen and powder fuel. The mixing efficiency of hydrogen fuel at the outlet of the double-hole jet is 0.728, which is 10% higher than that of the single-hole jet; The mixing efficiency of powder fuel is 0.342, which is 2% higher than that of the single-hole jet. However, the complex flow field structure of the double-hole jet leads to a large total pressure loss, about 0.74% higher than that of the single-hole jet.

Application of oscillation flow to horizontal gas–particle two-phase flow

The purpose of this study is to apply the oscillation flow induced by a combination of a circular cylinder and non-uniform soft fins to gas–solid two-phase flows to reduce the transport gas velocity and power consumption in a horizontal pipe. In order to evaluate the oscillation flow, several different sizes of square and circular cylinders are used to combine four pieces of soft fins with non-uniform lengths, which are mounted on the horizontal central plane in front of the particle supply. The test pipe comprises a horizontal acrylic pipe with a length of 5 m and an inside diameter of 80 mm. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test particles. The average gas velocity was 9–16 m/s, and the solid mass flow rate was 0.11–0.51 kg/s. It is found that the combination of a circular cylinder or square cylinder of L = 10 mm with non-uniform soft fins causes the lowest pressure drop and highest velocity fluctuation in the oscillation flow based on single-phase flow (gas only) measurement. Compared to conventional gas–solid two-phase flows, the reduction in the minimum transport velocity, pressure drop, power consumption, and additional pressure drop were obtained using a combination of a circular cylinder with non-uniform soft fins. This combination provides the highest reduction rates in the minimum conveying velocity and an additional pressure drop by approximately 10.0% and 34.1%, respectively. Based on particle image velocimetry measurements, the time-mean particle velocity and particle fluctuating velocity of a circular cylinder with non-uniform soft fins were higher than those of conventional flows near the bottom part of the pipe, thus easily accelerating and suspending particles near the pipe bottom, even at lower gas velocities.

Hydrodynamic modeling of non-swirling and swirling gas-particle two-phase turbulent flow using large eddy simulation

Flow structures of non-swirling and swirling particle-laden turbulence are modeled using the large eddy simulation. Four-way coupling to reveal the interaction mechanism of gas to particle, particle to gas and particle-particle collisions is adopted by a new proposed subgrid scale (SGS) particle kinetic energy-granular temperature model. Evolution of particle vortices, particle coherent structures and particle dynamics are predicted numerically, and comparisons are also conducted. Predictions are in good agreement with experimental measurements. For non-swirling flows, the typical coherent structures, and larger vortices at downward region of gas flow are dominantly. However, particle transport characteristics are significantly different, distinctly coherent structures and more vortices have not been generated in additions to fewer ones at far distance from entrance. Meanwhile, fewer coherent structures and vortices that dispersed at corner recirculation are observed for swirling flow. Compared to gas flow, the number of particle vortices is less and Reynolds stress and kinetic energy transport behaviors of particle flow are relatively independent due to inertia. Gas fluctuations of shear stresses are approximately twice greater than those of particle in non-swirling flows. A novelty finding is that turbulent fluctuations and instantaneous gas vortices of non-swirling flow are stronger than swirling case.

Unified gas-kinetic wave–particle method for gas–particle two-phase flow from dilute to dense solid particle limit

A unified framework for particulate two-phase flow is presented with a wide range of solid particle concentration from dilute to dense limit. The two-phase flow is simulated by two coupled flow solvers, that is, the gas-kinetic scheme (GKS) for the gas phase and unified gas-kinetic wave–particle method (UGKWP) for the solid particle phase. The GKS is a second-order Navier–Stokes flow solver. The UGKWP is a multiscale method for all flow regimes. The wave and particle decomposition in UGKWP depends on the cell's Knudsen number (Kn). At a small Kn number, the highly concentrated solid particle phase will be modeled by the Eulerian hydrodynamic wave due to the intensive particle–particle collisions. At a large Kn number, the dilute solid particle will be followed by the Lagrangian particle to capture the non-equilibrium transport. In the transition regime, a smooth transition between the above limits is obtained according to the local Kn number. The distribution of solid particles in UGKWP is composed of analytical function and discrete particle, and both condensed and dilute phases can be automatically captured in the most efficient way. In the current scheme, the two-phase model improves the previous one in many aspects, such as drag force model, the frictional pressure formulation, and flux limiting model. The scheme is tested in many typical gas–particle two-phase problems, including the interaction of shock wave with solid particle layer, horizontal pneumatic conveying, bubble formation, and particle cluster phenomena in the fluidized bed. The results validate the GKS-UGKWP for the simulation of gas–particle flow.

Particle-free zone of the two-phase flow in a convergent-divergent nozzle

The gas-particle two-phase flow in a convergent-divergent nozzle is encountered in many applications like solid-propellant rocket motors (SRMs). The “Particle-free Zone” adjacent to the nozzle wall is crucial for the nozzle performance which is closely related to the specific impulse of the motor. Though it has been usually observed by many investigators, the existence of the particle-free zone in different nozzles and its effect on nozzle performance are still ambiguous. In this research, we investigated the two-phase flow with monodispersed micron particles in a nozzle using a two-way coupled Eulerian-Lagrangian model and found that the particle-free zone does not exist for smallest particles (dp = 1.0 μm). Moreover, we built a theoretical model for predicting the extent of the particle-free zone by calculating the trajectory of the particle closest to the nozzle wall. The effects of the particle size, total pressure, total temperature and nozzle geometry on the particle-free zone were studied. Finally, we analyzed the nozzle performance and found that the gas velocity at the outlet and the thrust do not change with particle size monotonously, and the medium-sized particles cause the largest thrust loss.

Numerical Study on the Gas-Particle Two-Phase Jet Flow during Canister Launching Process

The Euler-Lagrange model of Jet-gas and AL2O3 is established to study the impact of gas-particle jet flow during canister launching process. The gas phase is the Navier-Stokes equation of the two-component transport of gas and air, and the turbulence model is the realizable two-equation model. The airflow flux is numerically discretized via AUSM format, and the viscous dissipation flux is a second-order central difference. The movement trajectories of particles with different diameters ranging from 1 to 100 μm and the distribution characteristics of jet flow dynamic parameters in the launching box are studied. The jet impingement flow field results of gas-particle two-phase flow are compared with those without particle phase. The results show that the particle phase has a retardation and heat transfer effect on the expansion of jet flow, which affects the distribution of jet flow parameters in the launch canister. Furthermore, compared with the pure jet flow impingement effect, the velocity of the two-phase jet flow along the central axis decreases and the temperature increases. Meanwhile, the trajectory of the particle phase is related to the particle diameter. As the diameter of the particles becomes smaller, the flow ability is better and affected by turbulence, and a random movement area in the downstream area of the jet is formed. As the diameter of the particles becomes larger, a particle aggregation area is formed on the jet axis due to inertial force.

Investigations of Gas–Particle Two-Phase Flow in Swirling Combustor by the Particle Stokes Numbers

Gas turbulence modulations and particle dispersions of swirling gas–particle two-phase flow in the combustor is investigated under the large spans of the particle Stokes numbers. To fully consider the preferential concentrations and anisotropic dispersions of a particle, a kinetic frictional stress model coupled with a second-order moment two-phase turbulent model and granular temperature equation is improved. The proposed modeling and simulations are in good agreement with the experimental validations. Results show turbulent modulations and particle dispersions exhibit strongly anisotropic characteristics, keeping a close relationship with flow structure. The axial gas velocity and RMS fluctuation velocity of 45.0-μm EGP was approximately 5.0 times and 3.0 times greater than 1000.0 μm Copper particles, and their axial particle velocity was 0.25 times and twice greater than those of 45.0 μm EGP. The degree of modulation in the axial–radial direction is larger than those of radial–tangential and axial–tangential direction. Particle dispersions are sensitive to particle diameter parameters and intensified by higher Stokes number.

Three-dimensional non-isothermal numerical model for predicting semi-volatile organic compound transport process in a room.

In this paper, a three-dimensional non-isothermal computational model for predicting indoor SVOC distribution is proposed, considering the effects of turbulence diffusion and suspended particles. The realizable k-ε model is introduced for turbulent flow simulation in a room. The Euler-Euler method is adopted to deal with the gas-particle two-phase flow coupled problem. Inertia slip velocity and irreversible first-order absorption boundary are employed for more accurate prediction of particle motion. The simulated curve of outlet gas-phase di-2-ethylhexyl phthalate (DEHP) concentration with emission time is verified by available experimental data. The emission process of DEHP in a 15m2 room in Beijing during 100days with or without air cleaner is simulated by the developed model considering air leak through window and door gaps. It is found that if the air cleaner keeps on all the time during 100days the gas-phase DEHP concentration in the room will tend to be uniform, while the emission process is far from equilibrium without an air cleaner even the emission lasts 100days. Results also suggest that floor heating, decrease of particle concentration, weaken of heat transfer, enhancement of mass transfer, and air infiltration in window gap contribute to decrease DEHP concentration.

Hydrodynamic Modeling of Turbulence Modulation by Particles in a Swirling Gas-Particle Two-Phase Flow.

Turbulence modulations by particles of a swirling gas–particle two-phase flow in an axisymmetric chamber are numerically simulated. To fully consider the preferential concentrations and the anisotropic dispersions of particles, a second-order moment model coupling particle–particle collision model was improved. Experimental validation for the proposed model, algorithm, and in-house codes by acceptable match was carried out. The effects of ultralight-expanded graphite and heavy copper particles with a large span of Stokes number on gas velocities and fluctuations, Reynolds shear stresses and tensor invariants, turbulence kinetic energies, and vortice structures are investigated. The results show that turbulent modulation exhibits strong anisotropic characteristics and remains in a close relationship with the flow structure. Modulation disturbances and vortex evolution are enforced by heavy-large particles with higher Stokes numbers. Preferential accumulations of ultralight particles in shear stress regions at lower vortices are weaker than those of heavy particles. For axial turbulence modulations, a heavy particle plays the primary role in the inhibition action because of larger inertia, and a light particle contributes to the enhancement effect due to excellent followability. The instantaneous flow information and coherent turbulent structure are failed to be acquired due to the limitation of the Reynolds time-averaged algorithm.

Investigation on Gas-Soot Flow Distribution Characteristic of Soot Capture Process in the Wall-Flow Diesel Particulate Filter

In order to investigate the distribution characteristics of gas-particle two-phase flow in the diesel particulate filter in the capture process, a mathematical model of gas-particle two-phase flow for inside-and-outside filter had been established in the capture process according to the mass conservation equation, momentum conservation equation, and k-ε turbulence equation. The model verification was carried out with the experimental and simulated of flow distribution characteristics of gas-particle two-phase. The obtained results showed that the static pressure gradient along the radial distribution was greater at the inlet of the filter in capture process in the diesel particulate filter, which could easily lead to causing eventual fatigue damage due to stress concentration in the front-end of filter; moreover, the weaker the vortex strength of gas-particle formed in expansion pipe was, the better uniformity of flow velocity and soot concentration distribution were. Therefore, the established mathematical model can be used for predicting gas-particle flow velocity distribution in the diesel particulate filter.