Interface-capturing Method Research Articles

Numerical study of droplet formation in a Y-junction microchannel

This study investigates the formation process of droplets in a Y-junction microchannel using two immiscible fluids: water as the continuous fluid and oil as the dispersed phase. We have examined the influence of the capillary number, flow rate ratio and viscosity ratio between the two fluids; parameters which determine the length and generation frequency of the droplets. Numerical simulations have been performed using the software Ansys Fluent with the interface capture method Volume of Fluid (VOF) for solving the governing equations. Three different algorithms have been tested for the pressure-velocity coupling: SIMPLE, SIMPLEC and PISO. The results are quite similar for SIMPLE and SIMPLEC, however it turned out that PISO is a better algorithm to solve the two-phase flow. Additionally, another Y-junction is coupled in the initial geometry to observe a symmetric breakup of the droplets and their formation is explained using the pressure field and the velocity field.

Effects of Matrix Metalloproteinase on Tumour Growth and Morphology via Haptotaxis

A tumour invasion model has been developed to examine the influence of diffusible matrix metalloproteinases (MMPs) and the mediated proteolysis of non-diffusible, membrane type MMPs (MT-MMPs) on tumour growth and morphology via haptotaxis. Our results are the first to explore the influence of localized degradation of extracellular matrix (ECM) by MT-MMPs on the morphology of tumours growing in nutrient-rich and nutrient-poor microenvironments. Two-dimensional numerical simulation, using a level-set-based tumour host interface-capturing method, reveals that haptotaxis due to ECM degradation by MMP causes greater instability than with ECM degradation by MT-MMP in low-nutrient environments, even at low proliferation rates; whereas the resulting morphologies are similar for high apoptosis rates. Our simulation results show that while haptotaxis leads to completely different tumour growth rates and morphologies depending on proliferation and apoptosis rates in low-nutrient environment, there are no significant variations when we compare the haptotaxis due to ECM degradation by MMP and MT-MMP, except for low proliferation rates. Focusing on the differences between MMP and MT-MMP mediated effects; our study has important implications in MMP-target validation and MMP-inhibitor-drug development for anti-cancer clinical trials.

Parallel load balancing strategy for Volume-of-Fluid methods on 3-D unstructured meshes

Volume-of-Fluid (VOF) is one of the methods of choice to reproduce the interface motion in the simulation of multi-fluid flows. One of its main strengths is its accuracy in capturing sharp interface geometries, although requiring for it a number of geometric calculations. Under these circumstances, achieving parallel performance on current supercomputers is a must. The main obstacle for the parallelization is that the computing costs are concentrated only in the discrete elements that lie on the interface between fluids. Consequently, if the interface is not homogeneously distributed throughout the domain, standard domain decomposition (DD) strategies lead to imbalanced workload distributions. In this paper, we present a new parallelization strategy for general unstructured VOF solvers, based on a dynamic load balancing process complementary to the underlying DD. Its parallel efficiency has been analyzed and compared to the DD one using up to 1024 CPU-cores on an Intel SandyBridge based supercomputer. The results obtained on the solution of several artificially generated test cases show a speedup of up to ∼12× with respect to the standard DD, depending on the interface size, the initial distribution and the number of parallel processes engaged. Moreover, the new parallelization strategy presented is of general purpose, therefore, it could be used to parallelize any VOF solver without requiring changes on the coupled flow solver. Finally, note that although designed for the VOF method, our approach could be easily adapted to other interface-capturing methods, such as the Level-Set, which may present similar workload imbalances.

A numerical investigation of nucleate boiling at a constant surface temperature

This study presents a 2D numerical investigation of nucleate boiling by a comprehensive model which includes systematic methods for multiphase simulation, e.g., the smoothed evaporation model, modified Height Function algorithm and the micro-layer model. The numerical framework employed in the present study is based on the VOF interface capture method, which is improved by implementing external functions. The modified Height Function yields a more accurate interface normal vector than the Youngs method and also presents smaller spurious velocities. Moreover, the Height Function shows good convergence with mesh refinement. In order to validate the comprehensive model, the growth of a bubble from a heated surface at a constant surface temperature is investigated. Based on the numerical results, the evolution of bubble size and local heat transfer at the contact line are quantified. The bubble shapes predicted in the numerical investigation agree well with experimental results; however, the departure time is longer than the experimental result. By considering the heat transfer within the bubble, it is shown that the vapor phase in the vicinity of the heating wall is superheated with a homogeneous gradient. Moreover, a detailed insight into bubble dynamics and local phenomena affecting the heat transfer during nucleate boiling is discussed.

An interface capturing method with a continuous function

A novel interface-capturing method is proposed to compute moving interfaces on unstructured grids with triangular (2D) and tetrahedral (3D) elements. Different from the conventional VOF (volume of ...

An Interface-Capturing Method for Free-Surface Flows in a Flow Channel Consisting of Solid Obstacles

An Interface-Capturing Method for Free-Surface Flows in a Flow Channel Consisting of Solid Obstacles

An interface capturing method with a continuous function: The THINC method on unstructured triangular and tetrahedral meshes

A novel interface-capturing method is proposed to compute moving interfaces on unstructured grids with triangular (2D) and tetrahedral (3D) elements. Different from the conventional VOF (volume of fluid) method which involves geometric reconstructions of the interface, the present method is based on the algebraic reconstruction approach originally developed in the THINC (tangent of hyperbola interface capturing) scheme by Xiao et al. (2005) [17]. A continuous multidimensional hyperbolic tangent function is employed for retrieving the jump-like distribution of the indicator function, which avoids the explicit geometric representation of the interface and thus substantially reduces the algorithmic complexity in unstructured grids. Numerical diffusion and smearing are effectively eliminated, and the compact thickness of the jump transition layer in the volume fraction is retained throughout the computation even for largely deformed interface. The solution quality of the present scheme is comparable to the VOF method with PLIC (piecewise linear interface calculation) algorithm.

Consistent numerical diffusion terms for simulating compressible multicomponent flows

An interface-capturing method using a high-order central difference scheme is presented for simulations of compressible multicomponent flows. The present method adds consistent numerical diffusion terms to robustly capture interface discontinuities, while maintaining the velocity, pressure, and temperature equilibriums at interfaces. Analysis of the numerical errors generated at the interfaces leads to a proposal of new consistent numerical diffusion terms. The method solves a fully conservative form of the total mass, momentum, total energy, and species-mass, and an additional advection form of the specific heats ratio to preserve the pressure oscillation-free property at the interfaces. Several one- and two-dimensional problems are used to verify the proposed method.

Computational and experimental study on local ship loads in short and steep waves

Currently, little information exists on the validity of interface-capturing methods in predicting local ship wave loads in short and steep waves. This study compares computational and experimental results in such a case (kA = 0.24, L wave /L ship = 0.16). The results allow the variation of wave loading between ten locations in the bow area of the ship to be observed. The computations were performed with an unstructured RANS solver that models free-surface flows with a volume-of-fluid method. In the model tests, the wave loads were measured with pressure sensors. The analysis of the results focuses on the wave conditions and on the pressure histories of the local wave loads. The computational and experimental results are in good qualitative agreement and encourage the further use of the computational results.

W241005 医学・工学、様々な分野へ応用可能な流体構造連成シミュレーション技術の開発(【W24100】若手研究者が目指す医工学テクノロジー-異分野間の最新動向の紹介-,医工学テクノロジー推進会議,バイオエンジニアリング部門,計算力学部門,機械力学・計測制御部門,ロボティクス・メカトロニクス部門,情報・知能・精密機器部門,流体工学部門企画,ワークショップ)

This paper presents advanced computer simulation techniques for nonlinear fluid-structure interaction problems. An interface-tracking method based on an arbitrary Lagrangian-Eulerian (ALE) finite element mesh technique and an interface-capturing method based on an extended finite element method (X-FEM) and Lagrange-multiplier method are presented, with several applications associated with material and engineering research divisions. The applications are also associated with and inspire to several medical applications.

A Fully Eulerian formulation for fluid–structure-interaction problems

In this work, we present a Fully Eulerian framework for fluid–structure interaction (fsi) problems coupling the incompressible Navier–Stokes equations with a hyperelastic solid.The Fully Eulerian framework is a monolithic implicit variational formulation for the coupled problem. In contrast to the well-established Arbitrary Lagrangian Eulerian (ALE) coordinates, the Fully Eulerian framework formulates both subproblems, fluid and solid, in Eulerian coordinates. This concept circumvents various difficulties connected to ALE coordinates since no artificial domain mapping is used. The formulation is an interface-capturing method and uses an extension of the solid’s deformation, the Initial Point Set, to detect the interface location.By construction, very large deformation as well as topology changes like contact of the solid to the domain boundary or other solid parts are possible.

THINC법을 이용한 비혼합 혼상류의 경계면 추적

기체와 액체의 유동 및 고체의 변형을 동시에 고려할 수 있는 혼상류모델을 이용하여 파동장을 해석하는 경우, 서로 다른 비혼합의 유체 경계면의 시간변형을 고정도로 추적하는 것이 대단히 중요하다. 본 연구에서는 경계면의 추적에 있어서 VOF(Volume of Fluid)법으로 대표되는 경계면 형상의 재구축이 필요한 Geometrical-type의 경계추적법의 대신에 Algebraic-type의 경계추적법인 THINC(Tangent of Hyperbola for INterface-Capturing)법을 적용하였다. THINC법은 경계면에 대한 형상의 구축이 필요하지 않으므로 VOF법에 비해 비교적 간단한 알고리즘을 가지며, 기존의 Navier-Stokes solver에로 적용성이 용이한 장점을 갖는다. 본 연구에서는 THINC법의 기본적인 이류특성을 고찰하고, 혼상류수치모델인 TWOPM(one-field Model for immiscible TWO-Phase flows)과 결합한 수치모델을 파동장에 적용하여 비혼합 혼상류에서 경계면의 추적능을 검토하였다. 그 결과, 혼상류의 경계면 추적에 있어서 상대적으로 간단한 알고리즘의 THINC법이 기존의 VOF법과 유사한 정도를 갖는 해석법이라는 것을 확인할 수 있었고, 따라서 향후 기포의 연행을 동반하는 쇄파 및 쇄파력의 해석 등에 그의 적용성이 기대된다. In the numerical simulation of wave fields using a multi-phase flow model that considers simultaneous flows of materials with different states such as gas, liquid and solid, there is need of an accurate representation of the interface separating the fluids. We adopted an algebraic interface capturing method called tangent of hyperbola for interface-capturing(THINC) method for the capture of the free-surface in computations of multi-phase flow simulations instead of geometrical-type methods such a volume of fluid(VOF) method. The THINC method uses a hyperbolic tangent functions to represent the surface, and compute the numerical flux for the fluid fraction functions. One of the remarkable advantages of THINC method is its easy applicability to incorporate various numerical codes based on Navier-Stokes solver because it does not require the extra geometric reconstruction needed in most of VOF-type methods. Several tests were carried out in order to investigate the advection of interfaces and to verify the applicability of the THINC method to wave fields based on the one-field model for immiscible two-phase flows (TWOPM). The numerical results revealed that the THINC method is able to track the interface between air and water separating the fluids although its algorithm is fairly simple.

Numerical investigation of the influence of companion drops on drop-on-demand ink jetting

In this study we characterized and investigated the specific phenomenon of "companion drops" in the drop-on- demand (DOD) ink jetting process. A series of simulations based on a piezoelectric DOD printhead system is presented, adapting the volume-of-fluid (VOF) interface-capturing method to track the boundary evolution and model the interfacial physics. The results illustrate the causality between the generation of companion drops and droplet deviation behavior, as well as their close correlations with ink jetting straightness and printing accuracy. The characteristics of companion drops are summarized and compared with those of satellite drops. Also, a theoretical mechanism for the generation of companion drops is presented, and their effects and behaviors are analyzed and discussed. Finally, the effects of critical factors on the generation of companion drops are investigated and characterized based on variations in the printable pressure range. Recommendations are given for the suppression of companion drops and for the improvement of printing accuracy.

Free surface flow around a ship model using an interface-capturing method

A free surface, turbulent flow code around ship hulls using the Slightly Compressible Flow formulation is used for simulating the flow around a Wigley hull. The code uses finite differences and the numerical scheme was marched in time using the 2nd order explicit Runge–Kutta method. Turbulent flows were simulated using the Baldwin–Lomax turbulence model. The grid is generated using an algebraic grid generator. The free surface treatment method is an interface-capturing one, on a fixed grid on which the kinematic free surface equation is solved. Several boundary conditions were implemented and their behavior was assessed. The flow conditions are the ones for which experimental and numerical results exist. The results show very good agreement with the experimental results.

Ejecting performance simulation of an innovative piezoelectric actuated lubrication generator for space mechanisms

A novel lubrication generator combing piezoelectric drop-on-demand (DOD) oil-jet technology is proposed for space mechanisms. A finite difference numerical model was established to analyze the design parameters of droplet ejection. The volume-of-fluid piecewise linear-interface construction (VOF-PLIC) interface-capturing method was adopted to represent the fluid domain and to track the evolution of its free boundaries whereas the continuous surface force (CSF) mode was chosen to model the interfacial physics. To explore the practicability of the proposed new lubrication generator, the flow behavior during the stages of fluid ejection and droplet formation are examined with Krytox 143AB lubricant as the baseline test fluid for a ejection cycle of 100 μs. To improve the droplet ejecting performance of lubricant, the characters of inject flow part have been investigated with the variation of the pulse voltage for different spatial temperature. Injection process in the extra-low pressure is also investigated. The developed model helps to understand the drop formation process and this approach can be applied in various inject head designs.

Anti-diffusion method for interface steepening in two-phase incompressible flow

In this paper, we present a method for obtaining sharp interfaces in two-phase incompressible flows by an anti-diffusion correction, that is applicable in a straight-forward fashion for the improvement of two-phase flow solution schemes typically employed in practical applications. The underlying discretization is based on the volume-of-fluid (VOF) interface-capturing method on unstructured meshes. The key idea is to steepen the interface, independently of the underlying volume-fraction transport equation, by solving a diffusion equation with reverse time, i.e. an anti-diffusion equation, after each advection time step of the volume fraction. As the solution of the anti-diffusion equation requires regularization, a limiter based on the directional derivative is developed for calculating the gradient of the volume fraction. This limiter ensures the boundedness of the volume fraction. In order to control the amount of anti-diffusion introduced by the correction algorithm we propose a suitable stopping criterion for interface steepening. The formulation of the limiter and the algorithm for solving the anti-diffusion equation are applicable to 3-dimensional unstructured meshes. Validation computations are performed for passive advection of an interface, for 2-dimensional and 3-dimensional rising-bubbles, and for a rising drop in a periodically constricted channel. The results demonstrate that sharp interfaces can be recovered reliably. They show that the accuracy is similar to or even better than that of level-set methods using comparable discretizations for the flow and the level-set evolution. Also, we observe a good agreement with experimental results for the rising drop where proper interface evolution requires accurate mass conservation.

Application of an Algebraic Interface Capturing Method to Wave Fields

In the present work, an algebraic interface capturing method called THINC is employed to track free-surface in computations of multi-phase flow simulations instead of geometrical-type methods such a VOF method. The THINC method uses a hyperbolic tangent functions to represent the surface, and compute the numerical flux for the fluid fraction functions. The main advantage of THINC is its easy applicability to incorporate various numerical codes because it does not require the extra geometric reconstruction needed in most of VOF-type methods. In order to verify the applicability of THINC to wave fields, several numerical simulations are performed based on the one-field model for immiscible two-phase flows (TWOPM). Comparisons are made between the numerical results and the experimental data, and good agreement is achieved.

Bounded renormalization with continuous penalization for level set interface‐capturing methods

AbstractIn this work, a reinitialization procedure oriented to regularize the level set (LS) function field is presented. In LS approximations for two‐fluid flow simulations, a scalar function indicates the presence of one or another phase and the interface between them. In general, the advection of such function produces a degradation of some properties of the LS function, such as the smoothness of the transition between phases and the correct position of the interface. The methodology introduced here, denominated bounded renormalization with continuous penalization, consists of solving by the finite element method a partial differential equation with certain distinguishing properties with the aim of keeping the desirable properties of the LS function. The performance of the strategy is evaluated for several typical cases in one, two and three‐dimensional domains, for both the advection and the renormalization stages. Copyright © 2010 John Wiley & Sons, Ltd.

IBM/ICM method for interactions between moving bodies and free surfaces

The IBM/ICM method is developed to simulate the interactions between moving bodies and free surfaces. This method is a combination of Immersed Boundary Method (IBM) and Interface Capture Method (ICM), inheriting the IBM's capability of using non-body conformal grids to represent the effect of a moving body in the flow by only adding a pseudo body-force in the right side of Navier-Stokes equations, as well as the capability of ICM, i.e. VOF, to capture the interface between two immiscible fluids. In the current paper, the Lagrange-multiplier based IBM method is employed and the volume of fraction (VOF) is introduced as an indicator function to mark the different fluids. The numerical method is validated by the case of high-speed impact by a horizontal circular cylinder, which exhibits a wide range of dynamical response characteristics, i.e. the formation of a cavity and induced pressure waves in the late stages of the cavity collapse, depending primarily on the projectile's impact velocity.

Influence of liquid hydrophobicity and nozzle passage curvature on microfluidic dynamics in a drop ejection process

Employing methods of computational fluid dynamics, we investigated the physical phenomena and fluid dynamics of a microfluid during ejection of a droplet with a designed system of a nozzle plate connected to a flat-plate piezoelectric material. A comparison between experimental measurements and numerical simulations was devised to validate the theoretical model. The volume-of-fluid piecewise linear-interface construction (VOF-PLIC) interface-capturing method was adapted to represent the fluid domain and to track the evolution of its free boundaries whereas the continuous surface force (CSF) mode was chosen to model the interfacial physics. The results show that the curvature of the flow channel affects the velocity, period before disintegration, volume of the droplet and number of satellite drops. Increasing the diameter of the orifice increases the volume and decreases the velocity of the droplet. Increasing the amplitude or frequency of the nozzle plate raises the input energy, so increasing the velocity, decreasing the volume and hastening the disintegration of the droplet, but an increased amplitude or frequency increases the number of satellite drops. At the hydrophobic boundary, the velocity increases, the droplet volume decreases and the period before disintegration is abbreviated because of the decreased adhesive force between the fluid and the boundary surface.