Fue Sang Lien

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Papers by Fue Sang Lien

A simple field function for solving complex and dynamic fluid-solid system on Cartesian grid

arXiv: Computational Physics, 2017

In this paper, a simple field function is presented for facilitating the solution of complex and ... more In this paper, a simple field function is presented for facilitating the solution of complex and dynamic fluid-solid systems on Cartesian grids with interface-resolved fluid-fluid, fluid-solid, and solid-solid interactions. For a Cartesian-grid-discretized computational domain segmented by a set of solid bodies, this field function explicitly tracks each subdomain with multiple resolved interfacial node layers. As a result, the presented field function enables low-memory-cost multidomain node mapping, efficient node remapping, fast collision detection, and expedient surface force integration. Implementation algorithms for the field function and its described functionalities are also presented. Equipped with a deterministic multibody collision model, numerical experiments involving fluid-solid systems with flow conditions ranging from subsonic to supersonic states are conducted to validate and illustrate the applicability of the proposed field function.

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Modelling 2D separation from a high lift aerofoil with a non-linear eddy-viscosity model and second-moment closure

The Aeronautical Journal

A computational study is presented, which examines the performance of variants of second-moment c... more A computational study is presented, which examines the performance of variants of second-moment closure and non-linear eddy-viscosity models when used to predict attached and separated flows over a high lift aerofoil for a range of incidence angles. The capabilities of both model types, especially in respect of resolving the onset of suction-side separation at high incidence, are contrasted with those of a low-Re k-ε model based on the linear Boussinesq stress-strain relationship. The second-moment model contains a conventional linear approximation of the pressure straining process; a cubic (realisable) variant has been investigated in an earlier study and found to offer no advantages. The quadratic eddy-viscosity model features coefficients which are sensitised to the strain and vorticity invariants. While both models, in the form originally proposed, are superior to the linear eddy-viscosity variant, neither performs well in respect of resolving separation, unless modified so as t...

Modelling Concentration Fluctuations from a Localized Source in Complex Urban Turbulent Flows

Proceeding of Sixth International Symposium on Turbulence and Shear Flow Phenomena

Numerical modelling of interaction between aluminium structure and explosion in soil

Applied Mathematical Modelling, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Comparison of implicit and explicit AUSM-family schemes for compressible multiphase flows

International Journal for Numerical Methods in Fluids, 2014

This paper makes the first attempt of extending implicit AUSM-family schemes to multiphase flow s... more This paper makes the first attempt of extending implicit AUSM-family schemes to multiphase flow simulations. Water faucet, air-water shock tube and oscillating manometer problems are used as benchmark tests with the generic four-equation two-fluid model. For solving the equations implicitly, Newton's method along with a sparse matrix solver (UMFPACK solver) is employed, and the numerical Jacobian matrix is calculated. Comparison between implicit and explicit AUSM-family schemes is presented, indicating that similarly accurate results are obtained with both schemes. Furthermore, the water faucet problem is solved using both staggered and collocated grids. This investigation helps integrate high-resolution schemes into staggered-grid-based computational algorithms. The influence of the interface pressure correction on the simulation results is also examined. Results show that the interfacial pressure correction introduces numerical dissipation. However, this dissipation cannot eliminate the overshoots because of the incompatibility of numerical discretization of the conservative and non-conservative terms in the governing equations. The comparison of CPU time between implicit and explicit schemes is also studied, indicating that the implicit scheme is capable of improving the computational efficiency over its explicit counterpart.

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A numerical framework for the direct simulation of dense particulate flow under explosive dispersal

Shock Waves, 2017

In this paper, we present a Cartesian grid-based numerical framework for the direct simulation of... more In this paper, we present a Cartesian grid-based numerical framework for the direct simulation of dense particulate flow under explosive dispersal. This numerical framework is established through the integration of the following numerical techniques: (1) operator splitting for partitioned fluid-solid interaction in the time domain, (2) the second-order SSP Runge-Kutta method and thirdorder WENO scheme for temporal and spatial discretization of governing equations, (3) the front-tracking method for evolving phase interfaces, (4) a field function proposed for low-memory-cost multimaterial mesh generation and fast collision detection, (5) an immersed boundary method developed for treating arbitrarily irregular and changing boundaries, and (6) a deterministic multibody contact and collision model. Employing the developed framework, this paper further studies particle jet formation under explosive dispersal by considering the effects of particle properties, particulate payload morphologies, and burster pressures. By the simulation of the dispersal processes of dense Communicated by D. Frost.

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Extension of staggered-grid-based AUSM-family schemes for use in nuclear safety analysis codes

International Journal of Multiphase Flow, 2017

To overcome the numerical difficulties of the density-based method for low-Mach-number two-phase ... more To overcome the numerical difficulties of the density-based method for low-Mach-number two-phase flow, this paper adopts the AUSM + and AUSMDV schemes based on a staggered-grid arrangement. The water faucet, air-water shock tube, oscillating manometer and air-water phase separation problems are used as benchmark tests to validate the implementation of the generic four-equation two-fluid model. The present results reveal the advantages of using staggered-grid-based AUSM + and AUSMDV schemes over the collocated-grid-based counterpart. With a staggered-grid arrangement, odd-even decoupling issues can be avoided. Thus, no sound speed scaling or additional diffusion terms are needed when using AUSM + and AUSMDV schemes for low-Mach-number two-phase flow. Furthermore, since the pressure and void fraction are already stored at the interface of the velocity control volume, no interpolation of interfacial pressure is needed for momentum equations. Finally, this study will help integrate AUSM + and AUSMDV schemes into staggered-grid-based thermal hydraulic codes, e.g. CATHENA, used in the nuclear industry. Moreover, to tackle the stiffness issues in relation to phase appearance and disappearance, we propose a new staggered-grid-based scheme referred to as AUSMFVS, which combines the accuracy of AUSM + and the stability of FVS.

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Assessment of ghost-cell based cut-cell method for large-eddy simulations of compressible flows at high Reynolds number

International Journal of Heat and Fluid Flow, 2015

Large-eddy simulations (LES) of high Reynolds number flows are performed using a non-body conform... more Large-eddy simulations (LES) of high Reynolds number flows are performed using a non-body conformal method in conjunction with a wall model. We use a simple wall function to model the wall-shear stress and the truncation error of the numerical discretization to model the sub-grid scale turbulence (implicit LES), although these can be easily replaced if necessary. The validation cases are: turbulent flow through an inclined channel, turbulent flow over a wavy surface, and supersonic flow over a circular cylinder. Since the near-wall grids are naturally coarse, the key is to use a method that is capable of capturing the flow dynamics accurately in the vicinity of the interface. Towards the purpose, we develop a Cartesian cut-cell method, referred to as the ghost-cell based cut-cell method (GC-CCM), in the context of fully compressible solutions of Navier-Stokes equations. This method employs ghost-cells inside the solid interface such that the local spatial reconstruction remains consistent everywhere including in the vicinity of the boundary. In order to capture the near-wall flow behavior more accurately with coarse grids, this method decomposes cell faces of merged cells and computes fluxes through each decomposed segment separately. The objective of this work is to qualify whether the proposed method can accurately represent the high Reynolds number flows in the vicinity of immersed interfaces. To analyze the performance of the proposed method, we compare the results to the corresponding numerical results from the two other non-body conformal methods, namely the ghost-cell based immersed boundary method (GCIBM) and standard cut-cell method (S-CCM), that are implemented in the same numerical solver. The comparison demonstrates that the proposed method is capable of capturing near-wall flows relatively accurately with coarse grids.

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Vertical plate fin with conjugated forced convection-conduction turbulent flow

ABSTRACT

Cartesian Anisotropic Mesh Adaptation for Compressible Flow

Simulating transient compressible flows involving shock waves presents challenges to the CFD prac... more Simulating transient compressible flows involving shock waves presents challenges to the CFD practi-tioner in terms of the mesh quality required to resolve discontinuities and prevent smearing. This paper dis-cusses a novel two-dimensional Cartesian anisotropic mesh adaptation technique implemented for compress-ible flow. This technique, developed for laminar flow by Ham, Lien and Strong in [2], is efficient because it refines and coarsens cells using criteria that consider the solution in each of the cardinal directions sepa-rately. In this paper the method will be applied to compressible flow. The procedure shows promise in its ability to deliver good quality solutions while achiev-ing computational savings. The convection scheme used is the Advective Up-stream Splitting Method (Plus) [7], and the refine-ment/coarsening criteria are based on work done by Ham et al. Transient shock wave diffraction over a backward step and shock reflection over a forward step are considered as test...

Computational Modeling of Aerosol Hazard Arising from the Opening of an Anthrax Letter in an Open-Office Complex

Early experimental work, conducted at Defence R&D Canada — Suffield, measured and characterized t... more Early experimental work, conducted at Defence R&D Canada — Suffield, measured and characterized the personal and environmental contamination associated with the simulated opening of anthrax-tainted letters under a number of different scenarios. A better understanding of the physical and biological processes is considerably significant for detecting, assessing, and formulating potential mitigation strategies for managing these risks. These preliminary experimental investigations have been extended to simulate the contamination from the opening of anthrax-tainted letters in an Open-Office environment using Computational Fluid Dynamics (CFD). Bacillus globigii (BG) was used as a biological simulant for anthrax, with 0.1 gram of the simulant released from opened letters in the experiments conducted. The accuracy of the model for prediction of the spatial distribution of BG spores in the office is first assessed quantitatively by comparison with measured SF6 concentrations (the baseline ...

Computational Modelling of 3D Turbulent Flow in S-Diffuser and Transition Ducts

Engineering Turbulence Modelling and Experiments, 1993

A non-orthogonal, collocated finite-volume algorithm is used, in conjunction with high-Re and low... more A non-orthogonal, collocated finite-volume algorithm is used, in conjunction with high-Re and low-Re variants of the k-e models and various convection schemes, to compute the flow in a S-diffuser and in two transition ducts, one involving a square-to-round and the other round-to-rectangular change in cross-sectional area. These geometries are considered, principally, in the context of air-intake ducts in turbo-jet powered aircraft. The low-Re k-e variants applied are new, having been formulated to adhere to constraints arising from length-scales prescribed as part of the one-equation models of Wolfshtein and Norris and Reynolds. The derivation of the former variant is summarised in this paper. The Results presented demonstrate that mean-flow features are generally well predicted and are largely insensitive both to the turbulence modelling practice and to the order of accuracy of the scheme used to approximate mean-flow convection. In contrast, the turbulence-energy field displays a much higher level of sensitivity to both numerical approximation and turbulence-model variations, this sensitivity being associated with near-wall turbulence generation coupled with convection by transverse motion or circulation.

Development of a Fast Physically-Based Urban Wind Flow and Dispersion Model for Emergency Response Applications

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Development of a Genetic Algorithm-Based Solution Algorithm for 1-D Convection-Diffusion Analyses

ABSTRACT RES

Efficient direct numerical simulation using multigrid with dynamic semi-coarsening

ABSTRACT

A Building-Resolved Wind Field Library for Vancouver: Facilitating CBRN Emergency Response for the 2010 Winter Olympic Games

Abstract : This memorandum describes some initial work to construct a wind field library consisti... more Abstract : This memorandum describes some initial work to construct a wind field library consisting of pre-computed building-aware mean wind and turbulence fields obtained from a high-resolution, high-fidelity computational fluid dynamics (CFD) model for a specific urban area; namely, for the downtown area of Vancouver and the surrounding environs for use in on-demand CFD in support of emergency response applications (requiring quick turnaround times) for the 2010 Winter Olympic Games. To this purpose, mean wind and turbulence field simulations were obtained for 32 wind directions using CFD over a model (computational) domain of 255 km2 (with a building-aware region of 10.4 km2 at 9-m horizontal resolution) centered on downtown Vancouver. An example illustrating the application of the wind field library for the rapid calculation of urban dispersion for a release of a hazardous material in downtown Vancouver is provided.

The Canadian Urban Dispersion Modeling (CUDM) System: Prototype Evaluation over Vancouver 2010

NATO Science for Peace and Security Series C: Environmental Security, 2011

The CUDM system provides transport and dispersion modeling capability at the urban scale. It simu... more The CUDM system provides transport and dispersion modeling capability at the urban scale. It simulates the mean flow, turbulence and concentration fields in urban areas. The system involves a cascade of meteorological models from the operational regional model to an urbanized meso-scale model that in turn drives a CFD flow model running at the urban scale. This CFD model simulates mean wind and turbulence fields that can feed dispersion models. The presentation will briefly describe the current state of the CUDM system, present results obtained over Vancouver during the Olympics and over Toronto during the G8/G20 summit meetings, and compare the different configurations.

Formation of particle jetting in a cylindrical shock tube

Shock Waves, 2013

A dense, solid particle flow is numerically studied at a mesoscale level for a cylindrical shock ... more A dense, solid particle flow is numerically studied at a mesoscale level for a cylindrical shock tube problem. The shock tube consists of a central high pressure gas driver section and an annular solid powder bed with air in void regions as a driven section with its far end adjacent to ambient air. Simulations are conducted to explore the fundamental phenomena, causing clustering of particles and formation of coherent particle jet structures in such a dense solid flow. The influence of a range of parameters is investigated, including driver pressure, particle morphology, particle distribution and powder bed configuration. The results indicate that the physical mechanism responsible for this phenomenon is twofold: the driver gas jet flow induced by the shock wave as it passes through the initial gaps between the particles in the innermost layer of the powder bed, and the chaining of solid particles by inelastic collision. The particle jet forming time is determined as the time when the motion of the outermost particle layer of the powder bed is first detected. The maximum num-Communicated by M. Brouillette.

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Prediction of second-order concentration statistics for dispersing plumes in obstacle arrays

Progress in Computational Fluid Dynamics, An International Journal, 2010

ABSTRACT In this paper, the turbulent dispersion of a passive scalar released from a continuous g... more ABSTRACT In this paper, the turbulent dispersion of a passive scalar released from a continuous ground-level point-source in two obstacle arrays is simulated using the Reynolds-averaged Navier-Stokes (RANS) method. An explicit algebraic nonlinear turbulent stress model and a tensor-diffusivity scalar-flux model are used for the closure of the ensemble-averaged momentum and scalar transport equations, respectively. The principal physical mechanisms governing the transport of the second-order concentration statistics of a passive scalar are modelled following Yee et al. (2009). The results of the simulation for the flow and concentration statistics are compared against two sets of high-quality water-channel measurement data obtained using laser induced fluorescence (for concentration) and laser Doppler anemometry (for velocity).

Acceleration and heating of metal particles in condensed matter detonation

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012

For condensed explosives, containing metal particle additives, interaction of the detonation shoc... more For condensed explosives, containing metal particle additives, interaction of the detonation shock and reaction zone with solid inclusions leads to high rates of momentum and heat transfer that consequently introduce non-ideal detonation phenomena. During the time scale of the leading detonation shock crossing a particle, the acceleration and heating of metal particles are shown to depend on the volume fraction of particles, dense packing configuration, material density ratio of explosive to solid particles and ratio of particle diameter to detonation reaction-zone length. Dimensional analysis and physical parameter evaluation are used to formalize the factors affecting particle acceleration and heating. Three-dimensional mesoscale calculations are conducted for matrices of spherical metal particles immersed in a liquid explosive for various particle diameter and solid loading conditions, to determine the velocity and temperature transmission factors resulting from shock compression...

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Fue Sang Lien

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