Level Contour Reconstruction Method Research Articles

Numerical simulation of the oil peeling mechanism on a hydrophilic plate dipping underwater

Peeling is a fundamental physical behavior involving the removal of foreign substances attached to a surface, and it finds applications in various engineering problems. Most previous studies have focused on peeling thin solid films from solid surfaces. However, ocean pollution has emerged as a serious environmental concern, making it critical to effectively and continuously remove highly viscous oil from oil recovery devices to prevent oil fouling. To address this, recent technological advancements have introduced an oil recovery technique that utilizes a hydrophilic surface capable of detaching, and even peeling, oil when dipped into water. In this study, we analyzed the underlying peeling mechanism by numerically simulating the oil peeling process from a vertically situated dipping plate with hydrophilic treatment. The present work expanded the level contour reconstruction method, originally developed for two-phase interface tracking, to handle the three-phase flow involved in the peeling of oil attached to the plate by an air–water meniscus. We properly validated the proposed numerical model and investigated the effects of various input conditions, including oil thickness, descending plate speed, and oil viscosity, in detail. Furthermore, force analysis during the oil peeling process was performed, and a regime map is provided to offer a comprehensive understanding of the overall peeling process. This research aims to contribute to the development of efficient and reliable oil recovery methods, particularly in combating ocean pollution caused by viscous oil residues.

Maximal spreading of droplet during collision on particle: Effects of liquid viscosity and surface curvature

This study uses the level contour reconstruction method to numerically investigate the maximum spreading due to droplet collision with a dry, stationary, spherical particle. We consider a broad range of impact conditions: Weber number 30–90, Ohnesorge number 0.0013–0.7869, and droplet-to-particle size ratio 1/10–1/2, and quantitatively and systematically analyze 120 collision cases to understand how liquid viscosity and surface curvature affect the maximum spreading. The maximum spreading increases on the smaller particles for both the capillary and viscous regimes, but the underlying physics clearly differ. The increase in maximum spreading is governed mainly by the surface deformation of the rim for the capillary regime and viscous dissipation for the viscous regime. An empirical correlation that can be applied to the droplet impact on both a particle and a flat surface is also presented. The model shows good agreement with existing experimental data as well as our simulation results within a deviation range of ±15%.

Computational study on dynamic behavior during droplet-particle interaction

In this study, the dynamic behavior of droplet collision with a dry, stationary, spherical particle was numerically investigated based on the level contour reconstruction method (LCRM). A broad range of impact conditions: Weber number (30 ≤ We ≤ 90), surface wettability (20° ≤ θeqi ≤ 175°), and droplet-to-particle size ratio (1/4 ≤ Ω ≤ 1/2), are considered, and three major impact outcomes: deposition, partial rebound, and complete rebound, are analyzed in detail. The dynamic spreading factor (for deposition cases), contact time (for complete rebound cases), and mass and momentum of the rebounded droplet (for partial rebound cases) were quantitatively investigated. The study quantitatively and systematically investigated the mass and momentum of (partially) rebounded droplets. We confirmed that the contact time of a (completely) rebounded droplet is independent of the surface curvature of the spherical particle as well as the impact velocity with the given impact conditions.

낙하하는 액적의 계면활성제 흡수 거동에 관한 수치 해석 연구

Surfactant, which has hydrophilic heads and hydrophobic tails, tends to accumulate at the phase interface. In general, surfactant decreases the surface tension coefficient locally, and thereby affects the dynamics of interface motion as well as flow characteristics. Although recent advances in numerical simulation for multiphase flow systems have made it possible to understand complicated interfacial phenomena interacting with surfactant, most of the existing numerical studies have mainly focused on the surfactant adsorption behaviors of rising bubbles so far. In this study, we attempt to analyze the effect from surfactant in the concentration field of external gas with a freely falling droplet. A Numerical model for tracking the movement of interface is proposed by using Level Contour Reconstruction Method (LCRM), and the governing equations for the surfactant transport are also formulated. Two benchmarking tests, i.e. Marangoni migration of a droplet, and a bubble rise interacting with surfactant, are performed to check the validity of proposed numerical formulation. Interaction behavior of surfactant with a freely falling droplet is compared with the case of rising bubble. In addition, the adsorption characteristics of surfactant during the free fall of a droplet are analyzed with various non-dimensional flow conditions. The absorption coefficient and the maximum surfactant concentration have been found to be the effective variables to increase the total absorption amount.

Direct numerical simulation of droplet collision with stationary spherical particle: A comprehensive map of outcomes

We use direct numerical simulation based on the level contour reconstruction method to investigate head-on droplet collisions with dry, stationary, spherical particles. Three important impact parameters are varied over broad ranges: Weber number (4 ≤ We ≤ 150), surface wettability (20° ≤ θeqi ≤ 160°), and droplet-to-particle-size ratio (1/3 ≤ Ω ≤ 2), leading to a total of 225 collision scenarios being examined. Seven collision outcomes are identified: deposition, partial rebound, complete rebound, complete coating, gravity disintegration, momentum disintegration, and splashing, and are represented in outcome regime maps. The first six outcomes are categorized into two cases: the partial-coating case (deposition, partial rebound, and complete rebound for larger particles) and the full-coating case (complete coating, gravity disintegration, and momentum disintegration for smaller particles), with a clear boundary separating the two cases in parameter space. The partial-coating case is characterized by maximum spreading and a subsequent recoiling that depends strongly on wettability. Conversely, the full-coating case involves complete initial wetting of the particle and the following dynamics is strongly governed by impact velocity. Detailed interaction mechanisms of each outcome scenario are also presented. Furthermore, three important quantitative parameters (i.e., film thickness, maximum spreading diameter, and coating time) are analyzed in detail.

Interaction of a deformable solid with two‐phase flows: An Eulerian‐based numerical model for fluid‐structure interaction using the level contour reconstruction method

SummaryWe describe the formulation of a method for fluid‐structure interaction involving the coupling of moving and/or flexible solid structures with multiphase flows in the framework of the Level Contour Reconstruction Method. We present an Eulerian‐based numerical procedure for tracking the motion and interaction of a liquid‐gas interface with a fluid‐solid interface in the Lagrangian frame together with the evaluation of the fluid transport equations coupled to those for the solid transport, namely the left Cauchy‐Green strain tensor field, in the Eulerian frame. To prevent excessive dissipation due to the convective nature of the solid transport equation, a simple incompressibility constraint for the strain field is enforced. A single grid structure is used for both the fluid and solid phases which allows for a simple and natural coupling of the fluid and solid dynamics. Several benchmark tests are performed to show the accuracy of the numerical method and which demonstrate accurate results compared to several of those in the existing literature. In particular we show that surface tension effects including contact line dynamics on the deforming solid phase can be properly simulated. The three‐phase interaction of a droplet impacting on a flexible cantilever is investigated in detail. The simulations follow the detailed motion of the droplet impact (and subsequent deformation, breakup, and fall trajectory) along with the motion of the deformable solid cantilever due to its own weight as well as due to the force of the droplet impact.

Numerical investigation of freely moving particle–droplet interaction with initial contact

We simulated freely moving particle–droplet interaction with initial contact. Fluid–structure interaction was modeled by fictitious domain method, and two-fluid interface was tracked using Level Contour Reconstruction Method. For tracking movement of the solid object, additional object distance function was calculated at Eulerian grid center. Since simple geometry, i.e., circle, was used in this study, object distance function can be easily computed from center location updated by averaged velocity to constrain solid movement. The interaction phenomenon was simplified as center-to-center contact without initial velocity. The gravitational acceleration was also ignored. We choose the size ratio and Ohnesorge (Oh) number as main parameters. Two characteristic behaviors were captured: the merging and separation case. Each velocity of the particle and droplet was shown to see the detailed evolution for merging and separation. In addition, two major forces acting on the particle, a capillary force and inertial force, were analyzed.

초소수성 실린더 표면에 충돌하는 액적의 움직임에 관한 수치해석 연구

Droplet impact is widely used in various engineering applications. Various conditions could affect the droplet evolution during impacting process. We have focused on geometrical effect from curved surface. Due to curvature of the wall, dynamics of the droplet would be quite different compared to the flat surface. We also paid great attentions to the contact line behavior. To augment the curvature effect, cylindrical surface with superhydrophobic characteristic was considered in this study. Very high advancing (165o) and receding angle (160o) associated with superhydrophobic surface makes distinctive difference in its behavior between axial and circumferential direction. We have numerical studied the impact process of the 3D droplet on cylindrical surface using Level Contour Reconstruction(LCRM) method. We found that impact behavior is pretty much same as flat surface in the axial direction. In circumferential direction, contact diameter has certain limit for higher impact velocity. Contact time of the droplet is also quite different compared to the flat surface in circumferential direction. At lower impact velocity, contact time of the droplet decrease rapidly with increased impact velocity but has negligible change at higher values.

A hybrid interface tracking – level set technique for multiphase flow with soluble surfactant

A formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu and Tryggvason (JCP 274 (2014) 737–757) [17] is adapted to the context of the Level Contour Reconstruction Method, LCRM, (Shin et al. IJNMF 60 (2009) 753–778, [8]) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that the adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows with a structured mesh. We also demonstrate that this approach applies easily to massively parallel simulations.

Numerical investigation of interaction between rising bubbles in a viscous liquid

The rising behavior of bubbles undergoing bubble-bubble interaction in a viscous liquid is studied using a two-dimensional direct numerical simulation. Level contour reconstruction method (LCRM), one of the connectivity-free front tracking methods, is applied to describe a moving interface accurately under highly deformable conditions. This work focuses on the effects of bubble size on the interaction of two bubbles rising side-by-side in a stagnant liquid. Several characteristics of bubble-bubble interaction are analyzed quantitatively as supported by energy analysis. The results showed clear differences between small and large bubbles with respect to their interaction behavior in terms of lateral movement, vortex intensity, suppression of surface deformation, and viscous dissipation rate. Distributions of vorticity and viscous dissipation rate near the bubble interfaces also differed depending on the size of the bubbles. Strong vortices from large bubbles triggered oscillation in bubble-bubble interaction and played a dominant role in the interaction process as the size of bubbles increases.

Numerical Simulation of Solid Liquid Interface Behavior During Continuous Strip Casting Process

A new metal-strip-casting process called continuous strip-casting (CSC) has been developed for making thin metal strips. A numerical simulation model to help understand solid-liquid interface behavior during CSC has been developed and used to identify the solidification morphologies of the strips and to determine the optimum processing conditions. In this study, we used a modified level contour reconstruction method (LCRM) and the sharp interface method to modify interface tracking, and performed a simulation analysis of the CSC process. The effects of process parameters such as heat-transfer coefficient and extrusion velocity on the behavior of the solid-liquid interface were estimated and used to improve the apparatus. A Sn (Tin) plate of dimensions 200 x 50 x 1 mm3 was successfully produced by CSC for a heat-transfer coefficient of 104 W/m2 K and an extrusion velocity of 0.2 m/s.

Analysis of Solid-Liquid Interface Behavior during Continuous Strip-Casting Process Using Sharp-Interface Technique

Continuous strip casting (CSC) has been developed to fabricate thin metal plates while simultaneously controlling the microstructure of the product. A numerical analysis to understand the solid-liquid interface behaviors during CSC was carried out and used to identify the solidification morphologies of the plate, which were then used to obtain the optimum process conditions. In this study, we used a modified level contour reconstruction method and the sharp-interface method to modify the interface tracking, and we performed a simulation analysis to identify the differences in the material properties that affect the interface behavior. The effects of the process parameters such as the heat transfer coefficient and extrusion velocity on the behavior of the solid-liquid interface are estimated and also used to improve the CSC process.

Direct numerical simulation of rising bubble interaction with free surface using level contour reconstruction method

Bubble rising phenomenon is widely found in many engineering applications including stream generators in power plants. Many experimental and numerical researches have been performed to predict the dynamic behavior of the bubble rising process. Most simulations so far have focused on evolution behavior of the rising bubble itself. Rising bubbles could penetrate through the top free surface which makes the problem much more complicated in addition to the curvature effect on the interface. With top surface, satellite droplets may be generated near breakup region and entrained to rising velocity field. In this paper, the effect of top free surface on rising bubble has been numerically investigated. High-order tetra-marching level contour reconstruction method (LCRM), which is a hybridization of fronttracking and level-set methods has been used to track the gas-liquid interface explicitly. Effects of free surface on the interfacial shape and behavior after breakup are studied with different size and depth of the initial bubble. It has been found that the initial diameter of the bubble is the dominant factor controlling the satellite droplet formation.

The Local Front Reconstruction Method for direct simulation of two- and three-dimensional multiphase flows

We present a new interface reconstruction technique, the Local Front Reconstruction Method (LFRM), for incompressible multiphase flows. This new method falls in the category of Front Tracking methods but it shares automatic topology handling characteristics of the previously proposed Level Contour Reconstruction Method (LCRM). The LFRM tracks the phase interface explicitly as in Front Tracking but there is no logical connectivity between interface elements thus greatly easing the algorithmic complexity. Topological changes such as interfacial merging or pinch off are dealt with automatically and naturally as in the Level Contour Reconstruction Method. Here the method is described for both two- and three-dimensional flow geometries. The interfacial reconstruction technique in the LFRM differs from that in the LCRM formulation by foregoing using an Eulerian distance field function. Instead, the LFRM uses information from the original interface elements directly to generate the new interface in a mass conservative way thus showing significantly improved local mass conservation. Because the reconstruction procedure is independently carried out in each individual reconstruction cell after an initial localization process, an adaptive reconstruction procedure can be easily implemented to increase the accuracy while at the same time significantly decreasing the computational time required to perform the reconstruction. Several benchmarking tests are performed to validate the improved accuracy and computational efficiency as compared to the LCRM. The results demonstrate superior performance of the LFRM in maintaining detailed interfacial shapes and good local mass conservation especially when using low-resolution Eulerian grids.

Numerical Simulation of Multiphase Flows by Level Contour Reconstruction Method (Improvement of Volume Conservation Property)

For multiphase flow simulations, accurate evaluation of interfacial tension is an important issue, so a front-tracking method which tracks the interface explicitly by marker elements is expected to be very useful. In the front-tracking method, however, treating the elements in 3D space is very tedious. To eliminate this problem, a front-tracking method without connectivity called level contour reconstruction method (LCRM) has been developed. However, the volume conservation property of the method is not so good. In this study, three techniques in reconstruction process of the LCRM are proposed and evaluated for several curvature spheres. As the result, the proposed method shows very high volume conservation property even for 2-grid diameter sphere. And also shape of a single deformable bubble and merging of two bubbles are reasonably expressed.

Simulation of droplet impact on a solid surface using the level contour reconstruction method

We simulate the three-dimensional impact of a droplet onto a solid surface using the level contour reconstruction method (LCRM). A Navier-slip dynamic contact line model is implemented in this method and contact angle hysteresis is accounted for by fixing the contact angle limits to prescribed advancing or receding angles. Computation of a distance function directly from the tracked interface enables a straightforward implementation of the contact line dynamic model in the LCRM. More general and sophisticated contact line models are readily applicable in this front tracking approach with few modifications, since complete knowledge of the geometrical information of the interface in the vicinity of the wall contact region is available. Several validation tests are performed including 2D planar droplet, 2D axisymmetric droplet, and full three-dimensional droplet splashing problems. The results show good agreement compared with existing numerical and experimental solutions.

Direct numerical simulation of multiphase flow for arbitrary geometry using level contour reconstruction method

Direct numerical simulation of multiphase flow on fixed Eulerian grid became increasingly popular due to its simplicity and robustness. Some of the well-known methods include VOF, Level Set, Phase field, and Front Tracking method. Lately, hybridization of above methods gets its attention to overcome the disadvantages pertaining to each method. One hybrid approach developed by the author is the Level Contour Reconstruction Method (LCRM) which combines characteristics of both Front Tracking and Level Set method. Many engineering problems also contain complex geometry as boundary condition and proper representation of grid structure plays very important role for the successful outcomes. In this paper, an algorithm for handling arbitrary geometry inside fixed Eulerian computational domain with multiphase flow has been presented. Interface reconstruction between liquid and vapor phase has been performed outside of arbitrary solid boundary explicitly along with dynamic contact angle model. Sharp interface technique using ghost fluid point extrapolation method has been utilized for correct implementation of no-slip boundary condition at the wall.

유체 유동을 동반한 다핵 수치상결정의 미세구조성장에 대한 수치해석적 연구

Most material of engineering interest undergoes solidification process from liquid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material thus the physical properties of final product. In this paper, effect of fluid convection on the dendrite solidification morphology is studied using Level Contour Reconstruction Method. Sharp interface technique is used to implement correct boundary condition for moving solid interface. The results showed good agreement with exact boundary integral solution and compared well with other numerical techniques. Effects of Peclet number and undercooling on growth of dendrite tip of both single and multiple seeds have been also investigated.

A hybrid interface method for three‐dimensional multiphase flows based on front tracking and level set techniques

AbstractSuccessful interface methods for multiphase flows need to be designed to operate well in the opposite extremes of strongly surface tension‐dominant flows on the one hand and strongly deforming flows on the other. To this end, recent advances in direct numerical simulation of multiphase flows have involved the hybridization of popular methods. One hybrid approach developed by the authors is the level contour reconstruction method (LCRM), which combines the characteristics of both the front tracking and the level set method. It was designed specifically for general 3D multiphase flow problems where very dynamic and deformable interfaces interact and where accuracy, reliability, and simplicity are essential features. In this paper, we carry the hybridization of the LCRM with the level set technique to a further level in that the explicit calculation of a distance function is introduced and plays a crucial role in the interface reconstruction procedure as well as in the calculation of the surface tension force. An accurate method of computing the distance function directly from the tracked interface is presented whereby a vector distance function is found, i.e. the minimum distance to the interface as well as the corresponding minimum distance point location on the interface itself. This information allows us to calculate a compact curvature field for the computation of the surface tension force, which decreases the level of parasitic currents to a negligible level. Various benchmark test cases to demonstrate the accuracy of the new schemes compared with other existing methods are provided. Copyright © 2008 John Wiley & Sons, Ltd.

Investigation of Thin Liquid Layer Rupture for Liquid-Protected Divertors

The liquid surfaces of liquid-protected high heat flux plasma-facing components may be subject to large temperature gradients caused by non-uniform incident particle and heat flux. Thermocapillary flows due to such gradients can potentially cause dry-out in high-temperature regions. Experimental and numerical investigations have been conducted to determine the maximum allowable non-dimensional temperature gradient just before rupture in thin liquid films of various aspect ratios and viscosities μ. Experiments were conducted using a needle contact method to measure the liquid film height of axisymmetric silicone oil (μ = 4.8 × 10-3 N·s/m2-9.6 × 10-1 N·s/m2) films for aspect ratios of 0.0065 to 0.02 on a non-isothermal stainless steel surface. The experimental data were compared with predictions from both an axisymmetric asymptotic analysis for the steady-state film height for thin layers and a direct numerical simulation using the level contour reconstruction method for thicker layers. The results of this investigation will provide component designers with experimentally-validated limits on the maximum allowable temperature radients to prevent local dry spot formation and possible burnout.