Browsing by Author "Lin, Shi-Wen"

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A FINITE-VOLUME-BASED APPROACH FOR DYNAMIC FLUID-STRUCTURE INTERACTION
(2013)
Tsui, Yeng-Yung
;
Huang, Yi-Cheng
;
Huang, Chun-Lung
;
Lin, Shi-Wen
;
機械工程學系
It is common to adopt finite-element methods to solve solid mechanics problems and finite-volume methods for fluid dynamics computations. The use of different methods causes complication of the solution procedure for problems involving both fluids and solids. In this study, a partitioned approach based on the finite-volume method for dynamic fluid-structure interaction is presented. The method is formulated in a way suitable for an unstructured mesh with arbitrary grid geometry. The variables for the fluid are stored at the centroids of grid cells, whereas those for the solid at the grid nodes. The latter arrangement makes it more suitable for large structure deformation. After spatial discretization for the solid using the finite-volume approach, the resulting system of ordinary differential equations is solved implicitly using the dual-time-stepping scheme. As for the fluid calculation, a pressure-based algorithm is employed and the time step is advanced in a prediction-correction manner. The finite-volume method for the solid is assessed by calculating the deformation and dynamics of a cantilever under various loads. Good agreement with analytical solutions is obtained. Then, the solution procedure is applied to two cases with coupled fluid flow and structure dynamics. One is the flow over a vertical plate with one end fixed on the floor in a channel. The other is the flow over a cylinder with a plate attached to it on the lee side.
A VOF-Based Conservative Interpolation Scheme for Interface Tracking (CISIT) of Two-Fluid Flows
(2013-04-01)
Tsui, Yeng-Yung
;
Lin, Shi-Wen
;
機械工程學系
;
Department of Mechanical Engineering
A simple interface-reconstruction scheme (CISIT), based on the volume-of-fluid (VOF) formulation and applicable to unstructured grids with arbitrary topology, is developed to track the interface in free-surface flows. The interface is represented by the contour surface of VOF value f=0.5, which is constructed simply by interpolation. The advancing of the interface is made by imposing mass conservation in the cells containing the interface. However, problems arise when the interface moves across the cell face and into another cell. The cell originally occupied by the interface may be overfilled (f>1) or underfilled (f<1) as the interface advances (moving in the positive direction of the interface) to leave the cell. In contrast, the cell may be overdepleted (f<0) or underdepleted (f>0) as the interface retreats (moving in the negative direction of the interface) to move out of the cell. These situations are remedied via adjusting the transported volume of fluid across the cell face by following the conservation law so that the VOF becomes 1 or 0 in these cells, depending on advancing or retreating of the interface. The resulting VOF distribution is uniform, either in 1 or 0, in the region outside the interface cells, and the interface occupies only one cell in its width. To smooth the fluid properties across the interface region in the velocity calculation, an average smoothing technique is adopted. Application to a number of test cases, including model cases with known velocities and a number of real flows, reveal that this method is accurate and robust.
Coupled level-set and volume-of-fluid method for two-phase flow calculations
(2017)
Tsui, Yeng-Yung
;
Liu, Cheng-Yen
;
Lin, Shi-Wen
;
機械工程學系
;
Department of Mechanical Engineering
In simulating two-phase flows, the volume-of-fluid (VOF) method has the advantage of mass conservation while with the level-set (LS) method, the surface tension force can be calculated more accurately. In this study, we present a coupling method which combines the advantages of both methods. The volume-of-fluid (VOF) method adopted in the calculation is the conservative interpolation scheme for interface tracking method proposed recently by the authors. Based on the location of the interface calculated from the VOF, the LS function is obtained by solving the equation used in the LS method for re-initialization without needing to solve its advection equation. A high-resolution-bounded scheme within the frame of finite-volume methods is used to solve the re-initialization equation. This scheme is verified by considering a variety of interface geometries. A circular bubble at equilibrium is used to assess the coupled LS and VOF method by examining the spurious currents generated in the bubble. Three-dimensional calculations are conducted to study the rising of a bubble in the quiescent water.
Flux-blending schemes for interface capture in two-fluid flows
(2009-11-01)
Tsui, Yeng-Yung
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Lin, Shi-Wen
;
Cheng, Tong-Ting
;
Wu, Tian-Cherng
;
機械工程學系
This paper is aimed at developing a robust algorithm (FBICS) to capture the interface between two immiscible fluids without the need of interface reconstruction. The advection equation of the volume fraction is solved using the fully conservative finite volume method. Determination of the convective flux through each cell face is based on blending of high resolution schemes and compressive schemes to preserve the sharpness and boundedness of the interface. The flux-blending practice is fulfilled with the use of flux limiters. Test on simple advection flow problems indicates that the well-known CICSAM and HRIC schemes lose accuracy as the Courant number increases. In contrast, the present method maintains high-accuracy performance for Courant numbers up to one. The capability of the method to cope with the complicated dynamics of free surface flows is demonstrated via calculation of the collapsing flow of a water column with an obstacle. (c) 2009 Elsevier Ltd. All rights reserved.
MODELING OF HEAT TRANSFER ACROSS THE INTERFACE IN TWO-FLUID FLOWS
(2014)
Tsui, Yeng-Yung
;
Lin, Shi-Wen
;
Ding, Kuen-Je
;
機械工程學系
;
Department of Mechanical Engineering
A model is presented in this article to deal with heat transfer across the interface separating two immiscible fluids. It is suitable to be incorporated into interface-tracking methods, such as volume-of-fluid (VOF) methods, because a sharp interface is available in these approaches. The temperature at the interface and the heat flux through it are calculated in such a way that the continuity of the two properties at the contact surface is satisfied explicitly. With use of these values, the temperature either at the centroid or on a face of the interface cell can be estimated, which serves as Dirichlet boundary condition for the energy equation. The temperature field is then calculated by solving the energy equations for the two fluids simultaneously in an implicit way. This method is first assessed via testing on two heat conduction problems in which two solids are in contact. Good agreement between numerical solutions and theory is obtained. To demonstrate its capability, it is applied to two kinds of heat transfer problems, one being the collapse of a heated water column in a cavity, and the other the falling of a molten tin droplet in an oil tank. The effect of fluid flow on the heat transfer is clearly illustrated.
Phase change calculations for film boiling flows
(2014-03-01)
Tsui, Yeng-Yung
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Lin, Shi-Wen
;
Lai, Yin-Nan
;
Wu, Feng-Chi
;
機械工程學系
A new VOF based interface tracking method, termed CISIT, developed by the present authors recently is extended to include heat and mass transfer due to phase change. In this method, the interface is represented by the contour surface of VOF value 0.5. The interface is advanced in a conservative predictioncorrection manner to ensure that the distribution of the VOF is a good approximation to the Heaviside function. An important issue related to the mass transfer across the interface is the treatment of the jump condition for the energy equation. The interface is tackled as an internal boundary for temperature field. The heat flux at the boundary is calculated separately in individual phase. However, unlike other studies, the energy equation for the two phases is solved simultaneously in an implicit way. This method is validated through tests on model problems for which theoretical solutions are available. Calculations are then performed to simulate boiling bubble flows emerging from a planar film and a circular film. The latter case also serves to demonstrate that the present methodology is applicable to phase change flows with irregular geometry. Different boiling modes are identified according to the superheated temperatures. (C) 2013 Elsevier Ltd. All rights reserved.
Pumping Flow in a Channel With a Peristaltic Wall
(2014-02-01)
Tsui, Yeng-Yung
;
Guo, Da-Ching
;
Chen, Shin-Hung
;
Lin, Shi-Wen
;
機械工程學系
Simplified models were widely used for analysis of peristaltic transport caused by contraction and expansion of an extensible tube. Each of these models has its own assumptions, and therefore, weakness. To get rid of the limitations imposed by the assumptions, a numerical procedure is employed to simulate this pumping flow in the present study. In earlier studies, the frame of reference adopted moves with the peristaltic speed of the vibrating wall so that the flow becomes steady. The flow characteristics in a wavelength were the main concern. In our calculations, a channel of finite length with a flexible wall is considered. Pressures are prescribed at the inlet and outlet boundaries. The computational grid is allowed to move according to the oscillation of the wall. Another state-of the-art technique employed is to construct the grid in an unstructured manner to deal with the variable geometry of the duct. The effects of dimensionless parameters, such as amplitude ratio, wave number, Reynolds number, and back pressure on the pumping performance are examined. Details of the peristaltic flow structure are revealed. Also conducted is the comparison of numerical results with the theoretical predictions obtained from the lubrication model to determine the suitability of this theory.
Three-dimensional modeling of fluid dynamics and heat transfer for two-fluid or phase change flows
(2016-02-01)
Tsui, Yeng-Yung
;
Lin, Shi-Wen
;
機械工程學系
;
Department of Mechanical Engineering
A numerical algorithm based on the VOF method was proposed to solve two-phase/two-fluid flow problems by the authors recently. Different from other surface reconstruction approaches, the interface between the two fluids is represented by a continuous surface as the contour surface of the VOF function. It is robust and easy to implement. In this article, the method is extended to deal with three-dimensional flows. Also considered in the study is the heat transfer in the flow with or without phase change. In order to validate the method, a variety of flow problems are under consideration and comparison with empirical correlations is made. The method is first tested by considering a benchmark case with prescribed 3-D velocity field. It is then applied to the problem of bubble rising in a quiescent liquid, followed by investigating the splashing of a drop impacting on a liquid film. To assess the heat transfer model for phase change, the boiling flow emerging from a superheated planar film is under investigation. The last one considered is a jet flow caused by injection of high-temperature octane into a water container. (C) 2015 Elsevier Ltd. All rights reserved.