Fluid-solid Interaction Force Research Articles

Combined immersed boundary and discrete unified gas kinetic scheme for the motion of an autonomous underwater vehicle model with slip over a solid-liquid interface

To improve the endurance and speed of an autonomous underwater vehicle (AUV), we consider adopting the slip over a solid-liquid interface, which has the effect of drag reduction. However, the simulation of motion of an AUV with the slip remains a challenge due to the fluid-structure interaction and multiscale problems involving the moving boundary. To solve these problems, the present work proposes a novel and competitive mesoscopic method. Firstly, the Discrete Unified Gas Kinetic Scheme (DUGKS) coupled with the immersed boundary method is improved by correcting the boundary force, avoiding any additional computational time or implementation effort. Its effectiveness and accuracy are validated by two numerical tests involving the moving boundary. Furthermore, a fluid-solid interaction force is introduced to this method to model the slip condition due to its easy and effective implementation. We perform the experiment of motion of an AUV model in water to further validate the proposed method, which shows that it can predict acceptable results. Then, the method is applied to study the effect of the slip on the motion of the AUV model. The greater slip induced by the fluid-solid interaction force has a greater effect on reducing the drag and improving the velocity. It is indicated that increasing the fluid-solid interaction force can increase the amplitude and decrease the oscillation frequency of the drag curve. Overall, the slip can improve the endurance and speed of the AUV model.

Dissipative Particle Dynamic Simulation of Oil-Water Two-Phase Flow in Quartz Slits

Aiming to study the characteristics and mechanism of oil-water two-phase flow, based on the method of dissipative particle dynamics (DPD), meso-scale models of pressure-driven flow in quartz slits with width of 5-15 nm were simulated. Water is the driving phase. The results show that, as the liquid flew, it stratified gradually. The stratification came earlier as the width, and the driving force increased. The flow in slit of 5 nm was slug flow, while velocity profiles in other models showed parabolic characteristics. When the liquid stratified, the velocity gradient in the near-wall area decreased as a result of the low momentum exchange rate between from water to oil. The density peaks of fluid appeared at the fluid-solid interface and the oil-water interface, caused by the fluid-solid interaction force and the oil-water repulsion, respectively. The oil phase showed stronger aggregation due to the attractive force from the wall. When the water saturation was 25%, the water phase was a water droplet surrounded by oil. When the water saturation was 75%, oil and water stratified. As the repulsive force between the two phases decreased, the surface tension decreased, the mixing degree increased, and the parabolic characteristics of the velocity profile were more obvious.

Minireview on Lattice Boltzmann Modeling of Gas Flow and Adsorption in Shale Porous Media: Progress and Future Direction

As an important unconventional resource, shale gas reservoirs have unique characteristics different from conventional oil and gas reservoirs. The ultrasmall pore sizes in shale induce the nanopore confinement effect on shale gas flow. In addition, shale rocks are rich in organic matter, which has strong interactions with gas molecules and results in gas adsorption. The lattice Boltzmann method (LBM) for micro- and nanoscale gas flow, which is originally designed for micro-electro-mechanical systems (MEMS), has been modified to simulate gas flow and adsorption in shale rocks. This work reviews four types of lattice Boltzmann models developed recently for shale gas flow/adsorption: (1) the slip-velocity-based LBM, (2) high-order LBM, (3) diffusion-based LBM, and (4) REV-scale LBM. Among these models, the slip-velocity-based LBM is widely used for shale gas modeling, which incorporates the slip boundary condition and Knudsen number (Kn)-determined relaxation time to simulate the nanopore confinement effect. To model the gas adsorption, the fluid–solid interaction force is introduced into the model, and the magnitude of this interaction force is usually obtained from the molecular level simulations. LBMs have been regarded as an efficient numerical tool to estimate the shale gas apparent permeability, to describe the pore-scale flow behaviors, and to address the influence of gas adsorption on shale gas storage and transport. Nevertheless, some challenges exist in current applications of LBMs for shale gas flow and adsorption simulations that are discussed in this minireview as well.

Numerical investigation of dynamic characteristics of debris bed formation based on CFD-DEM method

In a severe accident in nuclear reactor, the core meltdown occurs when nuclear fuel rods cannot be sufficiently cooled, thus forming debris beds with specific shapes on the lower head of the Reactor Pressure Vessel (RPV). In this paper, the fluid–solid interaction during debris bed formation is studied based on Computational Fluid Dynamics method coupled with Discrete Element Method (CFD-DEM). The CFD models are used to simulate the flow and pressure field of fluid, the DEM models are used to calculate the collision between solids and the collision between solids and wall, as well as the fluid–solid interaction force can be calculated by the two-way coupling models. The DEM models and CFD-DEM models were validated by different experiments. Based on the above models, the DEFOR-E7 test was simulated, and a conical debris bed formed by irregular debris with a static angle of 35° and a porosity of 72% was obtained. Therefore, the method and findings in this paper are significative on theory and application for the study of nuclear severe accidents.

Investigation of the characteristics and mechanisms of the layer inversion in binary liquid–solid fluidized beds with coarse particles

This paper adopts an optimized Euler–Lagrange method proposed in our previous work to study the characteristics and formation mechanisms of layer inversion in binary liquid–solid fluidized beds (LSFBs) with coarse particles. The LSFBs are formed in a cylindrical pipe with a diameter of 50 mm and a length of 0.6 m and consist of two species of coarse particles with different sizes: 6 mm glass spheres (species 1) and 10 mm glass spheres (species 2) with the particle density of 2600 kg/m3. First, the characteristics of the layer inversion of LSFBs with coarse particles are qualitatively analyzed. The positions of species 1 and species 2 are converted during layer inversion. Second, the changes in the trajectory and volume fraction of two species of particles are quantitatively investigated. Finally, the formation mechanisms of layer inversion with coarse particles are analyzed. The results show that the relative magnitude of the fluid–solid interaction force and the gravity is the main reason for determining the layer inversion of binary coarse particles of different sizes. The collision force is to balance the net force of the particle–fluid interaction force and the net gravity, so that the fluidized bed is in relative equilibrium. In addition, through the analysis of the evolution of the network of contact forces, the constraint of the wall on coarse particles is discussed during the layer inversion.

An improved lattice Boltzmann model for fluid–fluid–solid flows with high viscosity ratio

In this paper, we present an improved lattice Boltzmann model for fluid–fluid–solid (FFS) flows with a high viscosity ratio. The bounce-back particle model is combined with the Shan–Chen (SC) multicomponent model. We extend the bounce-back scheme based on velocity interpolation and a fresh-node initialization approach with second-order accuracy to moving particles within the framework of the multicomponent model. An improved virtual solid density model for wetting boundary conditions is employed to implement contact angles on curved boundaries. We examine the factors that lead to the violation of mass conservation, and an easy redistributing method is developed to fix the mass leakage issue. The combined multiphase particle model is able to simulate FFS flows with a high viscosity ratio of up to 1000 while preserving the total mass of the two fluids. The performance of the approach is tested by a variety of numerical experiments. The dynamic behaviors of moving contact lines on the curved boundary are validated by a droplet wetting on a solid particle. The model is then applied to simulate dynamic FFS problems, such as particle wetting at the fluid interface and particle motion through a fluid–fluid interface. According to the simulation results, the present model is capable of capturing the total force exerted on a particle by the fluid and the interface. However, the SC-type fluid–solid interaction force does not equal the capillary force in the present model. Finally, the self-assembly process of two floating particles on a liquid–liquid interface is investigated.

Kinetic theory of granular particles immersed in a molecular gas

The transport coefficients of a dilute gas of inelastic hard spheres immersed in a gas of elastic hard spheres (molecular gas) are determined. We assume that the number density of the granular gas is much smaller than that of the surrounding molecular gas, so that the latter is not affected by the presence of the granular particles. In this situation, the molecular gas may be treated as a thermostat (or bath) of elastic hard spheres at a fixed temperature. The Boltzmann kinetic equation is the starting point of the present work. The first step is to characterise the reference state in the perturbation scheme, namely the homogeneous state. Theoretical results for the granular temperature and kurtosis obtained in the homogeneous steady state are compared against Monte Carlo simulations showing a good agreement. Then, the Chapman–Enskog method is employed to solve the Boltzmann equation to first order in spatial gradients. In dimensionless form, the Navier–Stokes–Fourier transport coefficients of the granular gas are given in terms of the mass ratio$m/m_g$($m$and$m_g$being the masses of a granular and a gas particle, respectively), the (reduced) bath temperature and the coefficient of restitution. Interestingly, previous results derived from a suspension model based on an effective fluid–solid interaction force are recovered in the Brownian limit ($m/m_g \to \infty$). Finally, as an application of the theory, a linear stability analysis of the homogeneous steady state is performed showing that this state is always linearly stable.

Numerical prediction on minimum fluidization velocity of a supercritical water fluidized bed reactor: Effect of particle shape

Supercritical water fluidized bed reactor (SCWFBR) is a novel gasification reactor for hydrogen production. Compared with traditional hydrogen production technique, the SCW-based gasification has outstanding advantages such as high hydrogen production efficiency, no emission of gaseous pollutants, low water consumption and strong material adaptability. In this paper, based on Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations, numerical investigation is conducted on the effect of particle aspect ratio (α) on the minimum fluidization velocity (Umf) of a SCWFBR containing cylindrical biomass particles. The coupled CFD-DEM model is firstly validated against previously published experimental data. Then, the Umf for six types of particle shapes are calculated under different working conditions of temperature ranging from 633 to 693 K, pressure ranging from 25 to 27 MPa and α ranging from 1 to 6. Numerical results show that Umf increases with the temperature, but decreases with the pressure. Moreover, Umf is increasing with α. The underlying mechanisms are revealed by investigating the micro-structure of different shaped particles. It is shown that the increase of Umf with α is caused by the weakened fluid-solid interaction force and enhanced inter-particle locking. And the weakened fluid-solid interaction force is mainly due to the increase of the voidage. Finally, a predictive correlation of Umf for the SCWFBR is proposed considering α which demonstrates strong predictive capability for cylindrical particles.

A resolved CFD-DEM-IBM algorithm for water entry problems

A resolved CFD-DEM-IBM algorithm is proposed for elaborate numerical description of water entry process. Discretized on fixed Cartesian grids, the Navier-Stokes equations are adopted to describe the complex fluid behaviors. The motion of solid bodies and their interactions are modeled by the discrete element method (DEM). The immersed boundary method (IBM) is applied to track solid boundaries undergoing drastic movement by a series of Lagrangian points, on which the fluid-solid interaction forces are derived according to velocity boundary conditions. The free surface is captured using the improved conservation level set method which exhibits remarkable accuracy and mass conservation property. The partitioned scheme where several iterations are required is employed to realize tightly coupled fluid-solid system. Shown to be fully resolved where detailed resolution of fluid phase could be captured, the proposed method allows interaction among heterogeneous fields to be modeled with convincing accuracy. Several cases are performed to demonstrate the reliability of the algorithm whose results are in good accordance with the established data. Once validated, the proposed approach is applied to mimic water entry of multiple bodies, and particles settling in stratified fluid is conducted afterwards to reveal the versatility of the CFD-DEM-IBM algorithm for more general problems.

A dissipative particle dynamics study:influence of fluid-solid interaction force on micro-flow in shale slits

The fluid-solid interaction force has a decisive influence on the flow characteristics of micro-nano scale. Based on the dissipative particle dynamics (DPD) method, static and flow simulations of fluid in typical shale slits were carried out. The Lennard-Jones (LJ) potential function of 96X was applied to characterize the fluid-solid interaction force. The slit width ranged 3–10nm, the wall material was quartz, the fluid was n-hexane, and the driving force of the flow simulation ranged 1–20kcal/(mol·A). The results show that due to the attraction of solid wall, the aggregation of fluid molecules near the wall was enhanced, fluid density there increased, and the diffusion coefficient there was significantly lower than that in the middle of the slit. The fluidity of the fluid near the wall is significantly reduced. In the flow model, when the fluid-solid interaction force was ignored, the flow profile was piston-like, and the velocity gradient at the edge of the slit was extremely large, showing the characteristics of slip flow. When the fluid-solid interaction force was taken into account, the velocity was reduced significantly, and the profile was parabolic. When the LJ96X was replaced by LJ126X potential function to characterize the fluid-solid interaction force, the attractive force from the wall on the fluid near the wall decreased, the fluidity was enhanced, and the velocity profile increased. When the conservative force parameter of fluid was changed, enhancing the wettability of oil phase, the affinity between fluid and solid was increased, and the velocity profile was reduced.

The Simulation of Liquid Flow in the Pore Network Model of Nanoporous Media

Abstract The fluid–solid interaction force shows significant influence on liquid flow at nanoscale. Vast experimental observations in recent literatures have shown that Darcy's law cannot be applied to nanoporous media. In this study, the slip length and effective viscosity are adapted to characterize the nanoscale effect. First, the nanoscale effect is investigated in nanotubes through computational fluid dynamic (CFD) modeling analysis. Slip boundary condition has been studied as an important discrepancy between macroscopic flow and nanoscale liquid flow. The effect of viscosity change becomes more notable with the slip length increasing. Then, the flow equation for pore network modeling is developed to capture nanoscale effect. The results show that the apparent permeability of nanoscale systems is significantly underestimated when slip effect is neglected. The size of the pore throat determines whether the slip effect needs to be considered, and critical diameter of neglecting the slip effect for circular throat is 79.17 Ls. It is necessary to take the variation of effective viscosity into account under slip boundary condition. With the pore throat size decreasing, the nanoscale effect increases. The nanoscale effect is more sensitive to pore throat size under hydrophobic conditions than hydrophilic conditions.

An SPH Approach for Non-Spherical Particles Immersed in Newtonian Fluids.

Solid particles immersed in a fluid can be found in many engineering, environmental or medical fields. Applications are suspensions, sedimentation processes or procedural processes in the production of medication, food or construction materials. While homogenized behavior of these applications is well understood, contributions in the field of pore-scale fully resolved numerical simulations with non-spherical particles are rare. Using Smoothed Particle Hydrodynamics (SPH) as a simulation framework, we therefore present a modeling approach for Direct Numerical Simulations (DNS) of single-phase fluid containing non-spherically formed solid aggregates. Notable and discussed model specifications are the surface-coupled fluid–solid interaction forces as well as the contact forces between solid aggregates. The focus of this contribution is the numerical modeling approach and its implementation in SPH. Since SPH presents a fully resolved approach, the construction of arbitrary shaped particles is conveniently realizable. After validating our model for single non-spherical particles, we therefore investigate the motion of solid bodies in a Newtonian fluid and their interaction with the surrounding fluid and with other solid bodies by analyzing velocity fields of shear flow with respect to hydromechanical and contact forces. Results show a dependency of the motion and interaction of solid particles on their form and orientation. While spherical particles move to the centerline region, ellipsoidal particles move and rotate due to vortex formation in the fluid flow in between.

Modified immersed boundary method for flows over randomly rough surfaces

Many phenomena, ranging from biology to electronics, involve flow over rough or irregular surfaces. We treat such surfaces as random fields and use an immersed boundary method (IBM) with discrete (random) forcing to solve resulting stochastic flow problems. Our approach relies on the Uhlmann formulation of the fluid-solid interaction force; computational savings stem from the modification of the time advancement scheme that obviates the need to solve the Poisson equation for pressure at each sub-step. We start by testing the proposed algorithm on two classical benchmark problems. The first deals with the Wannier problem of Stokesian flow around a cylinder in the vicinity of a moving plate. The second problem considers steady-state and transient flows over a stationary circular cylinder. Our simulation results show that our algorithm achieves second-order temporal accuracy. It is faster than the original IBM, while yielding consistent estimates of such quantities of interest as the drag and lift coefficients, the length of a recirculation zone in a cylinder's wake, and the Strouhal number. Then we use the proposed IBM algorithm to model flow over cylinders whose surface is either (deterministically) corrugated or (randomly) rough.

Wood–Moisture Relationships Studied with Molecular Simulations: Methodological Guidelines

This paper aims at providing a methodological framework for investigating wood polymers using atomistic modeling, namely, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Atomistic simulations are used to mimic water adsorption and desorption in amorphous polymers, make observations on swelling, mechanical softening, and on hysteresis. This hygromechanical behavior, as observed in particular from the breaking and reforming of hydrogen bonds, is related to the behavior of more complex polymeric composites. Wood is a hierarchical material, where the origin of wood-moisture relationships lies at the nanoporous material scale. As water molecules are adsorbed into the hydrophilic matrix in the cell walls, the induced fluid–solid interaction forces result in swelling of these cell walls. The interaction of the composite polymeric material, that is the layer S2 of the wood cell wall, with water is known to rearrange its internal material structure, which makes it moisture sensitive, influencing its physical properties. In-depth studies of the coupled effects of water sorption on hygric and mechanical properties of different polymeric components can be performed with atomistic modeling. The paper covers the main components of knowledge and good practice for such simulations.

Uniqueness of poroelastic and viscoelastic nonlinear inversion MR elastography at low frequencies

Intrinsic actuation MR elastography (IA-MRE) exploits natural pulsations of the brain as a motion source to estimate mechanical property maps. The low frequency motion of IA-MRE introduces new considerations for inversion algorithms relative to traditional external actuation MRE. Specifically, inertial forces become very small, which leaves low frequency viscoelastic inversions with a non-unique scalar multiplier. Biphasic poroelastic inversions include additional fluid–solid interaction forces to balance the elastic forces, which avoids the non-uniqueness. Analyzing the convergence behavior from different starting values using 1 Hz simulated data, IA-MRE data from a gelatin phantom and in vivo brain IA-MRE data reveal that higher frequency (50 Hz) viscoelastic inversion reaches the correct, unique solution regardless of initial property estimate; whereas, low frequency viscoelastic inversion recovers relative values of shear modulus. In the presence of measurement noise, the non-unique scalar multiplier is determined by the softest material reaching the prescribed lower bound on shear modulus. Poroelastic inversion produces a unique solution at both 50 Hz and 1 Hz; however, hydraulic conductivity must be known or accurately estimated in order to recover quantitatively accurate shear modulus maps at low frequency.

A unified grayscale lattice Boltzmann model for multiphase fluid flow in vuggy carbonates

In addition to intrinsic matrix pores, ranging in size from submicrons to microns, vuggy carbonates often contain significantly larger vug spaces. Immiscible multiphase fluids flowing through this type of microporous systems exhibit complicated flow mechanisms that are involved in the interactions between multiphase fluids and different types of pore spaces. Modeling multiphase fluid flows requires using the appropriate governing equations for different porosity systems. More specifically, while multiphase Darcy's equations might hold for a matrix system, they are not applicable for a vug system. To improve understanding this difficult multiphase flow problem in vuggy carbonates, we developed a unified grayscale lattice Boltzmann (LB) model for multiphase flows. The proposed model combines the generalized LB model in porous media with the pseudo-potential multiphase approach by adding the fluid-fluid interaction force, the fluid-solid interaction force, and the linear and nonlinear drag forces induced by the porous matrix. The model is still within the framework of the generalized LB model, and it switches freely from the Darcy's regime to the free-flow regime via rock property (i.e., porosity). It can also extend to a wide range of porosity systems because we incorporated both the linear and nonlinear drag effects. A continuous flow interface between the porous matrix and the vug region is captured by simulation without incorporating complex interface boundary conditions between the two porosity systems. The current model is validated and calibrated with theory, and then it is applied to a number of test cases. The test cases include the simulations of two-phase displacement in non-vuggy porous media, isolated vuggy porous media, and connected vuggy (fractured) porous media. Moreover, the effect of vug spaces on the interface-front speed and the breakthrough time is investigated. In addition, we simulated water displacing oil in two real vuggy carbonate cores imaged using low-resolution and high-resolution X-ray computed microtomography, and we investigated the effects of matrix heterogeneity, vug connectivity, and matrix wetting preference.

Numerical prediction of thin liquid film near the solid wall for hydraulic cavitating flow in microchannel by a multiphase lattice Boltzmann model

Based on a multiphase lattice Boltzmann (LB) model integrating body forces such as inter-particle interaction force and fluid-solid interaction force, a numerical prediction of thin liquid film near the solid wall for hydraulic cavitating flow in microchannel is conducted in the present work. The validity of model is tested by means of Laplace law and experimental result. On this basis, a full thin liquid film near the solid wall is successfully predicted, which proves that the single-component multiphase LB model integrated with various interaction forces is a good solution to this type of problem like hydraulic cavitating flow in microchannel. The further simulation indicates that the fluid-solid interaction strength (gs) has a significant effect on the formation of thin liquid film. A critical value (gs = −3.5) of fluid-solid interaction strength is found, and thin liquid film fails to be predicted at gs > −3.5. A simple simulation on the contact angle (θ) of droplet on the solid surface is conducted to analyze the reason for this phenomenon. It is found that a full thin liquid film could be successfully predicted only when the solid surface is fully wetted by liquid, i.e., θ = 0° corresponding to gs ≤ −3.5. The current research provides a potential way for future investigation on heat transfer accompanied by hydraulic cavitating flow.

Simulation of Mixed Convection in Eccentric Annulus: A Combined Lattice Boltzmann and Smoothed Profile Approach

ABSTRACTLattice Boltzmann Method is used to simulate mixed convection between two horizontal cylinders. This geometry is created using Smoothed Profile Method which produces proper fluid-solid interaction force as well as heat exchange. A two dimensional double distribution function lattice Boltzmann method is employed to simulate fluid flow and heat transfer simultaneously. In order to implement the velocity and temperature boundary conditions, the force term and heat source/sink are included in the evolution equations. While fixed Eulerian lattice nodes are employed, while different eccentricities are considered for inner cylinder. In order to simulate mixed convection, the radius ratio is set to be 2.5. Furthermore, the effect of Richardson number by choosing 0.01, 1, 100 and Prandtl number of 0.716 for air and 6.2 for water are investigated. Isotherms, streamlines and mean Nusselt numbers are given for each case. The results are in good agreement with previous related publications.

Lattice Boltzmann simulation of liquid flow in nanoporous media

In this paper, a multi-relaxation-time lattice Boltzmann (LB) model for nanoscale liquid flow is established to investigate the liquid flow characteristics in nanoporous media. The slip length and effective viscosity obtained by molecular dynamics (MD) simulations are adopted to account for the nanoscale effect. First, the LB model for water flow in nanopores is built and water flow characteristics in nanoporous media are investigated. The fluid-solid interaction force shows significant influence on water flow in nanoporous media. The water flux through nanoporous media increases with the decrease of fluid-solid interaction force. In hydrophobic nanoporous media, the nanoscale effect can decrease the gap between water flow resistance in large pores and that in small pores, making the velocity distribution more uniform. In addition, the end effect caused by the bending of streamlines can induce significant additional flow resistance. Neglecting the end effect can greatly overestimate water flow ability. The pore structure also has significant influence on water flow in nanoporous media. With the increase of specific interfacial length, the nanoscale effect increases. Finally, the LB model for oil (octane) flow in quartz nanopores is also established by incorporating the MD simulation results. Oil flow simulation in quartz nanoporous media shows that the conclusions obtained for water flow are also applicable for oil flow.

Fluid-Solid Boundary Handling Using Pairwise Interaction Model for Non-Newtonian Fluid

In order to simulate fluid-solid boundary interaction for non-Newtonian Smoothed Particle Hydrodynamics (SPH) fluids, we present a steady and realistic fluid-solid boundary handling method using symmetrical interaction forces. Firstly, we use the improved SPH method to model the non-Newtonian fluid. Secondly, the density of boundary particle is created into the calculation of fluid-solid interaction forces. Besides, we apply friction conditions to constrain the fluid particles at the boundary. Finally, we apply the predictive-corrective scheme to correct the density deviation and improve boundary computing efficiency. The experiment confirms the feasibility for the interaction between non-Newtonian fluid and solid objects with this method. At the same time, it reflects the viscous characteristics and ensures the physical properties of non-Newtonian fluid. In addition, compared to existing methods, this method is more stable and easier to implement.