Immersed Boundary Lattice Boltzmann Research Articles

Flow-Induced Transverse Vibration of Three Equal-Diameter Cylinders in an Equilateral Triangle Using the Immersed Boundary–Lattice Boltzmann Flux Solver

Flow-Induced Transverse Vibration of Three Equal-Diameter Cylinders in an Equilateral Triangle Using the Immersed Boundary–Lattice Boltzmann Flux Solver

Numerical analysis of an oscillating square and circular bluff body submerged in the wake of an identical static bluff body: A GPU Accelerated Immersed Boundary-Lattice Boltzmann Approach

Hydrodynamic forces acting on marine structures, tubes, and objects can trigger disruptive vibrations. This study is an effort to encapsulate the results of wake induced vibration among tandem bodies. Specifically, impact of a static upstream body on a downstream oscillating body at Reynolds number 100 and constant frequency ratio Fr=1.0. The effects of streamwise displacement are investigated in a tandem arrangement of 1.05≤Lx/D≤12.0. In this study an in-house developed code employed that combines an immersed boundary lattice Boltzmann method with a structural equation and is accelerated using a graphical processing unit. When comparing scenario 1 (both bodies oscillate) to scenario 2 (only the downstream body oscillates), the study finds that the upstream square body motion has little effect on the downstream square body oscillation. However, the upstream circular body motion significantly impacts the downstream body oscillation. In addition, the study observes that the maximum amplitude occurs after reaching the critical spacing in scenario 2, whereas it occurs at and after the critical spacing in scenario 1. The critical spacing ratio is similar in both scenarios but varies for square and circular bodies. Lastly, the study examines the flow physics and hydrodynamic force coefficients of the downstream oscillating body.

Vortex synchronization-enabled heat-transfer enhancement in a channel with backward- and forward-facing steps

A channel with one backward-facing step and one forward-facing step is a typical configuration in engineering applications. In the channel, good heat transfer performance is often required, and the enhancement is usually achieved by employing different passive control methods, such as modification of geometric configuration or application of nanofluid. However, the other control method, i.e., active flow control (AFC), which is likely more effective, has been rarely applied in such a scenario. This study aims to bridge this gap by exploring how a rigid plate affects the heat transfer of the channel. The plate either is stationary or actively rotates, corresponding to passive flow control or AFC. The influences of the horizontal position of the plate (S) and its orientation angle (θ) on the heat transfer performance are studied when the plate is stationary to provide a baseline. Compared to the baseline, the effects of S, θ, and the rotation frequency (fr) are revealed when the plate undergoes a sinusoidal rotation. Such a thermo-fluid dynamic problem is numerically simulated by the immersed-boundary lattice Boltzmann method. The results show that the plate can improve the heat transfer performance no matter whether it rotates or not, compared to the case without a plate. The rotating plate outperforms the stationary one when θ and fr are properly chosen at each S. Substantial improvement can be achieved when vortex synchronization or resonance occurs in the channel, i.e., when the natural vortex shedding frequency is close or equal to fr.

Effects of Different Motion Parameters on the Interaction of Fish School Subsystems.

For a long time, fish school swimming has attracted a great deal of attention in biological systems, as fish schools can have complex hydrodynamic effects on individuals. This work adopted a non-iterative, immersed boundary-lattice Boltzmann method (IB-LBM). A numerical simulation of two-dimensional three-degree-of-freedom self-propelled fish, in side-by-side, staggered, and triangle formations, was conducted by adjusting spacing and motion parameters. A comprehensive analysis of individual speed gains and energy efficiencies in these formations was carried out. Furthermore, an analysis of the hydrodynamic characteristics of fish schools was performed, using instantaneous vorticity profiles and pressure fields. Certain studies have shown that passive interactions between individuals cannot always bring hydrodynamic benefits. The swimming efficiency of side-by-side formations in the same phase gradually increases as the distance decreases, but it also brings certain burdens to individuals when the phases are different. This paper also shows that the roles of passive interactions, spacing, and deflections affect fish school subsystems differently. When the low-pressure areas created by a wake vortex act on one side of an individual's body, the tail-end fish are good at gaining hydrodynamic benefits from it. This effect is not universal, and the degree to which individuals benefit from changes in exercise parameters varies. This study provides a theoretical basis for bioinspired robots, as well as providing certain insights into the mechanism of collective biological movement.

Suspensions of viscoelastic capsules: effect of membrane viscosity on transient dynamics

Membrane viscosity is known to play a central role in the transient dynamics of isolated viscoelastic capsules by decreasing their deformation, inducing shape oscillations and reducing the loading time, that is, the time required to reach the steady-state deformation. However, for dense suspensions of capsules, our understanding of the influence of the membrane viscosity is minimal. In this work, we perform a systematic numerical investigation based on coupled immersed boundary–lattice Boltzmann (IB-LB) simulations of viscoelastic spherical capsule suspensions in the non-inertial regime. We show the effect of the membrane viscosity on the transient dynamics as a function of volume fraction and capillary number. Our results indicate that the influence of membrane viscosity on both deformation and loading time strongly depends on the volume fraction in a non-trivial manner: dense suspensions with large surface viscosity are more resistant to deformation but attain loading times that are characteristic of capsules with no surface viscosity, thus opening the possibility to obtain richer combinations of mechanical features.

Stability Improvement of the Immersed Boundary–Lattice Boltzmann Coupling Scheme by Semi-Implicit Weighting of External Force

The immersed boundary–lattice Boltzmann (IB-LB) coupling scheme is known as an efficient scheme for fluid–structure interactions (FSIs). However, the conventional IB-LB schemes suffer from instability because they involve a high-Reynolds-number flow or a larger stiffness structure. An averagely weighted iteration approach is presented to improve the stability restriction in this paper. This new approach, which improves the stability by mitigating the high-frequency fluctuations, is implemented by iteratively calculating the external force, and averagely weighting the force obtained at every iterative step. Five cases are simulated to verify the accuracy and effectiveness of the present approach. Under the premise of maintaining the accuracy of the conventional IB-LB method, the implementation of the present approach can significantly enhance the numerical stability. Compared with the conventional IB-LB method, the present approach can significantly expand the material parameter range for simulation; in particular, this approach qualitatively improves the upper limit of the bending rigidity coefficient by approximately 8000 times. To use the outstanding stability of the present approach, the IB inertia force can be directly incorporated into the simulation. In addition, under the low-viscosity condition, the present approach can effectively simulate the large-deformation FSI problem.

The effects of particle shape, orientation, and Reynolds number on particle-wall collisions

Crystallisation is an important unit operation used in the production of Active Pharmaceutical Ingredients (APIs). Crystallisation is typically carried out using seed crystals in a process called secondary nucleation that allows for greater control of crystal quality attributes. The mechanism of secondary nucleation is still not well understood. Particle attrition is one proposed mechanism. This work examines the conditions under which particle-wall collisions occur. This is done through the simulation of free-moving particles in an impinging jet flow using an immersed-boundary lattice Boltzmann method (IB-LBM) CFD solver. Particle Reynolds numbers from 100 to 400 are examined. Particle shapes with aspect ratios from 1:1 to 8:1 are used to represent the crystal habits of APIs.Particles that start in their low-drag or high-drag orientation maintain this orientation on approach to the target surface. All other intermediate initial orientations examined cause particles to rotate toward and overshoot their high-drag form before adopting their high-drag form in proximity to the target surface. Particles in their low-drag form remain in their initial orientation due to the symmetry of the computational domain. In this orientation, a collision is most likely to occur, and the minimum critical Reynolds number at which a particle-wall collision will occur can be determined. This value is shown to increase with increasing particle frontal length. Pointed or rounded leading edges are shown to improve a particle's ability to pierce the boundary layer adjacent to the target surface and reduce this value. In cases where a Reynolds number of 400 is insufficient to cause a particle-wall collision, the particles’ minimum distances from the target surface are reported. Using the minimum critical Reynolds number values obtained, the approach velocities required for particles to collide with a wall are shown to be larger than the impeller tip speeds typically used during crystallisation operations. This work provides for the first time the conditions under which particle-wall collisions occur for varying shape and orientation, their behaviour on approach, and the associated impact velocities.

Influence of the corner radii on the flow characteristics of three square-like cylinders in an equilateral-triangular arrangement using IB-LBM

A two-dimensional momentum exchange-based immersed boundary–lattice Boltzmann method (IB-LBM) is used to scrutinize the influence of the corner radii on the characteristics of laminar flow around square-like cylinders arranged in an equilateral-triangular configuration, with each cylinder represented by 300 discrete elements. Numerical simulations were carried out in Newtonian flow with viscous, incompressible, and constant properties, by simultaneously changing the corner ratio λ from 0.0 (square) to 1.0 (circular), Reynolds number Re from 40 to 160, and gap ratio δ from 0.5 to 5.0. The wake flow patterns, force coefficients, and Strouhal number St were calculated and discussed. The numerical outcomes demonstrate that the corner ratio, Re, and gap ratio have a prominent influence on the flow characteristics. The wake flow patterns in the λ-Re plane can be divided into steady-state, flip-flopping, anti-phase, and in-phase modes for δ = 3.0. The drag Cd and lift Cl coefficients exhibit a decreasing trend with increasing corner radius except for Clc1; as δ is increased, the Cl of all three cylinders for λ ranging from 0 to 1.0 gradually approached zero. The St of the steady state flow pattern is significantly lower than that of other flow states, the relationship between St and λ is complex and irregular; as δ increases, the St and λ show a positive correlation.

A Non-Equilibrium Interpolation Scheme for IB-LBM Optimized by Approximate Force

A non-equilibrium scheme and an optimized approximate force are proposed for the immersed boundary–lattice Boltzmann method (IB-LBM) to solve the fluid–structure interaction (FSI) equations. This new IB-LBM uses the discrete velocity distribution function and non-equilibrium distribution function to establish the interpolation operator and the spread operator at the mesoscopic scale. In the interpolation operator, we use the force model of LBM to derive a direct force with a simple form. In the spread operator, we give a theoretical proof with local second-order accuracy of the spread process using the non-equilibrium theory from the LBM. A non-iterative explicit force approximation scheme optimizes the direct force in that the streamlines have no penetration phenomenon, and the no-slip condition is strictly satisfied. Different from other schemes for the IB-LBM, we try to apply the non-equilibrium theory from the LBM to the IB-LBM and obtain good results. The explicit force obtained using the non-equilibrium scheme and then optimized via the non-iterative streamline correction equation simplifies the explicit direct force scheme and the original implicit scheme previously proposed but obtains a similar streamline correction result compared with the implicit method. Numerical tests prove the applicability and accuracy of this method in the simulation of complex conditions such as moving rigid bodies and deforming flexible bodies.

A VOS based Immersed Boundary-Lattice Boltzmann method for incompressible fluid flows with complex and moving boundaries

A Volume of Solid (VOS) based Immersed Boundary-Lattice Boltzmann Method (IB-LBM) in the framework of the direct forcing based IB-LBM model has been developed in this work to simulate the fluid flow with complex and moving boundaries efficiently. In the present model, the concept of VOS is introduced to achieve the field extension to the solid phase, and a unified Lattice Boltzmann Equation (LBE) has been obtained to describe the fluid flow and the solid body motion consistently. To solve the resulting unified LBE, an efficient direct forcing model has been developed. Compared with the traditional surface based IB model with the direct forcing strategy, in the present work, the dependency of the Lagrangian grid to describe the body profile on the background Cartesian grid is removed by modelling the solid body with a Level-Set function. With such Level-Set description about the body surface, the VOS function can be obtained for the further field extension. With the present IB-LBM algorithm, the motion of the solid body can be enforced effectively without iterations about the forcing term compared with the implicit velocity correction or multiple velocity correction based IB algorithm, and flow penetration, which has been observed in the explicit velocity correction based IB model, can be reduced considerably. To achieve the velocity adjustment in the solid phase, an optimal forcing factor is recommended. With such optimal factor, the unphysical oscillation during force prediction can be well controlled. To verify the performance of the present model, a series of typical benchmarks, including the fluid flow caused by general shaped fixed or moving structures, hydrodynamic characteristics of thin-wall bodies undergoing specified motions and even more complex vortex induced vibrations, are conducted and the good agreements between the present results and the well-validated previous ones confirm the reliability and robustness of the present model.

The effects of particle shape on inertial focusing

This paper proposes a 2D particle inertial focusing model by the immersed boundary–lattice Boltzmann method (IB-LBM), aiming to study the effects of particle shapes on their focusing state. First, as the validation, we investigated the inertial focusing of circular particles and got consistent focus positions with other previous reports. Then, the inertial focusing of the circle, rectangle, ellipse, and capsule particles were studied in detail. The results revealed that the particle shapes significantly influence the focusing positions, self-rotation, and running speed. At a given Reynolds number, the circular particle has a minimum average distance to the pipe center in the focus state, then follows the elliptical, capsular, and rectangular particles. The elliptical particle’s self-rotation cycle is in approximately the cubed relation to the long-short axis ratio. Moreover, the rectangle particle runs fastest at the same Reynolds number, followed by capsule, ellipse, and circle particles. Our study and the above results can provide a significant reference for screening or separating particles with different shapes in microfluidic devices.

Partial confinement effects on the performance of a flapping foil power generator

The impacts of partial confinement on the power extraction performance of a flapping foil generator at a Reynolds number of 1100 are numerically studied using an immersed boundary–lattice Boltzmann method. Four confinement levels are implemented with two thin plates of finite size symmetrically placed at the distance of 1.5, 2, 3, and 4 foil chord length from the neutral position of the flapping foil. Parametric studies on plate lengths varying from 10 to 50 foil chord lengths at the four confinement levels are conducted. The results show that the power-extraction efficiency increases nearly monotonically with the upstream plate lengths while the impact of the downstream plate lengths is much less significant, indicating that upstream confinement is the dominant factor influencing the power-extraction performance. Contrary to the performance improvement observed in studies on the effect of infinite walls, the efficiency decreases dramatically with the decrease in the distance from the plates to the foil. The reasons for the dramatically decreased performance due to confinement effects are found. First, the interactions between the boundary layer of the plates and leading edge vortices formed on the foil reduce the size of the low-pressure region on the suction surface of the foil, leading to reductions in lift forces and consequently to major reductions in the extracted power. In addition, large mass flow deficits between the finite plates are observed when the distance between the two plates is small, indicating substantial reductions in potential power that can be extracted from the inflow.

Reduced model for droplet dynamics in shear flows at finite capillary numbers

Droplet deformation at finite capillary numbers is accurately studied in shear flows via Immersed Boundary - Lattice Boltzmann (IB-LB) simulations. A reduced model is introduced to capture nonlinear effects in droplet deformation and orientation.

Flight dynamics in forward flights of cabbage white butterfly

We conducted measurements of a butterfly’s motion in forward flight and numerical simulations using a computational model reflecting its motion. We measured the motion of a cabbage white butterfly (Pieris rapae), and then we constructed a computational model composed of a thorax, an abdomen, and four wings (i.e., left and right wings with fore and hind parts). Furthermore, we calculated the flow field and aerodynamic force and torque generated by the butterfly model using the immersed boundary–lattice Boltzmann method. In this simulation, we considered two types of periodic motions corresponding to slightly-descending and ascending forward flights. As a result, we found that the wing-tip and leading-edge vortices are formed on the wings and then released backward and downward in both flights. The major difference between the two flights is the flapping amplitude, indicating that the butterfly changes the flapping amplitude for each period and increases it to ascend. In addition, we considered a chimera model whose motion is based on the slightly-descending flight but partly given by the ascending flight. As a result, we found that the pitching angle and the angle of attack determine the traveling direction, but simply changing these angles does not achieve the ascending flight due to insufficient lift force. Thus, the butterfly should adjust the flapping and lead–lag angles in response to the pitching angle and the angle of attack to change the flight mode.

Thermal free-surface immersed-boundary lattice Boltzmann method for free surface flows with a liquid-solid phase transition

This paper reports on the progress of the liquid-solid phase transition modeling of water in open channel flow by using the lattice Boltzmann method with the immersed boundary modification. The phase transition in a fluid flow has a moving interface between the liquid and solid state, which leads complicated treatments in existing numerical models. By applying the immersed boundary modification in the lattice Boltzmann method and the non-iterative enthalpy approach for the separation of the states, the moving boundary of the melting or solidification front is solved without any difficulty. The ice bed and the submerged ice cover under dynamic flow conditions is exercised to demonstrate the model performance. The model is extremely suitable in the formulation in terms of its simple and compact framework extendable to any dimensions.

Study of Rotation Effect on Nanofluid Natural Convection and Heat Transfer by the Immersed Boundary-Lattice Boltzmann Method

Aiming to investigate the rotation effect on the natural convection and heat transfer of nanofluid, which has an important application in the control of heat transfer, the velocity field and temperature distribution inside the square cylinder with the rotating heat source in the center were numerically studied and presented in detail at different Hartman numbers and aspect ratios using the immersed boundary-lattice Boltzmann method. Then, the average Nusselt number on the surface of the heat source was calculated to compare the heat transfer rate in different cases. The results showed that the rotation would reduce the effect of gravity on the flow and suppress the heat transfer between the rotating heat source and nanofluid, while the external magnetic field would reduce the rotation effect on the flow and suppress or promote the heat transfer depending on the rotational speed and aspect ratio. Moreover, the smaller aspect ratio of the heat source to the square cylinder would enhance the heat transfer rate and make the retarding effect of magnetic field on rotation more apparent. In addition, the dimensionless rotational speed was proposed in this work, by which much computational time could be saved during the calculation of the immersed-boundary lattice Boltzmann method for the problem of rotation.

Numerical simulation for deformation characteristic of tea shoot under negative pressure guidance by the immersed boundary–lattice Boltzmann method

At present, due to the shortage of tea picking labour force, realizing the mechanized picking of famous tea is urgent. Using negative pressure guidance is a feasible method, which can compensate the localization error of machine vision. In this paper, tea shoot with one bud and two leaves is taken as the study object, and a ‘Y-type’ tea physical model is established according to its physical properties. Moreover, the deformation characteristic of tea shoot under negative pressure guidance is studied by using the immersed boundary–lattice Boltzmann method. The purpose is to analyse the effects of pressure P inside the pipe, vertical deviation H and horizontal deviation W on the deformation characteristics of tea shoot quantitatively. The effectiveness of the numerical calculation method is verified by the negative pressure guiding test. The results show that the success rate of negative pressure guidance is 100% when the leaf span d ≤ 30 mm and the horizontal deviation W ≤ 10 mm. The useful data and insights into the picking technology of famous tea based on negative pressure guidance are provided in this paper according to the findings mentioned above.

Inertial migration of soft particles initially evenly spaced along the flow direction in a channel

The inertial migration of two-dimensional soft particles initially distributed uniformly in channel flow is numerically studied by employing an immersed-boundary lattice Boltzmann method coupled with a finite element method. To model a soft particle, a capsule with an elastic membrane separating the liquid inside from the outside is used. Validation tests show excellent agreement with previous numerical results of other researchers. Then, the effects of the number of capsules Np, the bending stiffness Eb, the initial position Y0′, and the Reynolds number Re on the dynamics of the capsules in channel flow are investigated in detail. Interestingly, we discover a new regime (labeled as regime E) in which a few capsules situated near the channel centerline travel much faster than the rest. Moreover, regime E is more prone to vanishing while the capsules are very soft. The normalized overall lateral position of the capsules σ increases almost linearly with Np when the capsules stabilize in a single-line particle train (designated as regime A). We also make an effort to explain the formation of the capsule deformation shape in regime A. The steady dynamics of a single capsule depend on whether the initial position is on the channel centerline. However, if the capsule is not released on the channel centerline, the steady capsule dynamics are independent of the initial position. But, it is not true for multiple capsule dynamics. These findings may help understand the inertial migration of capsules in channel flow.

Computational assessment of immersed boundary–lattice Boltzmann method for complex moving boundary problems

Computational assessment of immersed boundary–lattice Boltzmann method for complex moving boundary problems

Point-to-Point Navigation of a Fish-Like Swimmer in a Vortical Flow With Deep Reinforcement Learning

Efficient navigation in complex flows is of crucial importance for robotic applications. This work presents a numerical study of the point-to-point navigation of a fish-like swimmer in a time-varying vortical flow with a hybrid method of deep reinforcement learning (DRL) and immersed boundary–lattice Boltzmann method (IB-LBM). The vortical flow is generated by placing four stationary cylinders in a uniform flow. The swimmer is trained to discover effective navigation strategies that could help itself to reach a given destination point in the flow field, utilizing only the time-sequential information of position, orientation, velocity and angular velocity. After training, the fish can reach its destination from random positions and orientations, demonstrating the effectiveness and robustness of the method. A detailed analysis shows that the fish utilizes highly subtle tail flapping to control its swimming orientation and take advantage of the reduced streamwise flow area to reach it destination, and in the same time avoiding entering the high flow velocity area.