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Article
Publication date: 2 January 2018

Mark Ho, Guan Heng Yeoh, John Arthur Reizes and Victoria Timchenko

Interface distinct two-phase computational fluid dynamics (CFD) simulations require accurate tracking in surface curvature, surface area and volume fraction data to precisely…

141

Abstract

Purpose

Interface distinct two-phase computational fluid dynamics (CFD) simulations require accurate tracking in surface curvature, surface area and volume fraction data to precisely calculate effects such as surface tension, interphase momentum and interphase heat and mass transfer exchanges. To attain a higher level of accuracy in two-phase flow CFD simulations, the intersection marker (ISM) method was developed. The ISM method has cell-by-cell remeshing capability that is volume conservative, maintains surface continuity and is suited for the tracking of interface deformation in transient two-phase flow simulations. Studies of isothermal single bubbles rising in quiescent water were carried out to test the ISM method for two-phase flow simulations.

Design/methodology/approach

The ISM method is a hybrid Lagrangian–Eulerian front tracking algorithm which can model an arbitrary three-dimensional surface within an array of cubic control volumes. Fortran95 was used to implement the ISM method, which resulted in approximately 25,000+ lines of written code and comments. To demonstrate the feasibility of the ISM algorithm for two-phase flow simulations, the ISM algorithm was coupled with an in-house CFD code, which was modified to simulate two-phase flows using a single fluid formulation. The constitutional equations incorporated terms of variable density and viscosity. In addition, body force source terms were included in the momentum equation to account for surface tension and buoyancy effects.

Findings

The performance of two-phase flow simulations was benchmarked against experimental data for four air/water bubbles with 1, 2.5, 5 and 10 mm of diameter rising in quiescent fluid. A variety of bubble sizes were tested to demonstrate the accuracy of the ISM interface tracking method. The results attained were in close agreement with experimental observations.

Practical implications

The results obtained show that the ISM method is a viable means for interface tracking of two-phase flow CFD simulations. Other applications of the ISM method include simulations of solid–fluid interaction and other immersed boundary flow problems.

Originality/value

The ISM method is a novel approach to front tracking, and the results shown are original in content.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 18 March 2022

Xiang Fang, Anthony Chun Yin Yuen, Eric Wai Ming Lee, Jiyuan Tu and Sherman Cheung

The purpose of this paper is to investigate the development process of the fire whirl in the fixed-frame facility and focus on the impacts of the fire whirl’s vortex core on the…

112

Abstract

Purpose

The purpose of this paper is to investigate the development process of the fire whirl in the fixed-frame facility and focus on the impacts of the fire whirl’s vortex core on the formation and flame structure of the fire whirl.

Design/methodology/approach

The complex turbulent reacting flame surface is captured by the large eddy simulation turbulence closure coupled with two sub-grid scale (SGS) kinetic schemes (i.e. the chemistry equilibrium and steady diffusion flamelet). Numerical predictions are validated thoroughly against the measurements by Lei et al. (2015) with excellent agreements. A double maximum tangential velocity refinement approach is proposed to quantify the vortex cores’ instantaneous location and region, addressing the missing definition in other studies.

Findings

The numerical results show that the transition process of the fire whirl is dominated by the vortex core movement, which is related to the centripetal force. The unsteadiness of the fully developed fire whirl was found depending on the instantaneous fluctuation of heat release rate. The steady diffusion flamelet scheme is essential to capture the instantaneous fluctuation. Furthermore, the axial velocity inside the vortex core is the key to determining the state of fire whirl.

Practical implications

Due to intensive interactions between buoyant fires and ambient rotating flow, the on-set and formation of fire whirl still remain largely elusive. This paper focused on the transition process of fire whirl between different development stages. This paper provides insights into the transition process from the inclined flame to the fire whirls based on the centripetal force.

Originality/value

This paper presented and compared two SGS kinetic schemes to resolve the fire whirl development process and the unsteadiness of its vortical structures. The modelling framework addresses the shortcoming of previous numerical studies where RANS turbulence closure and simplified combustion kinetics was adopted. Numerical results also revealed the fire whirl transition process and its relationship to centripetal force.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 10
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 October 2019

Cathryn H. Clayton

In the past 20 years, Macao has experienced phenomenal economic growth driven by the liberalization of its casino sector. This growth has been enabled by massive influxes of…

262

Abstract

Purpose

In the past 20 years, Macao has experienced phenomenal economic growth driven by the liberalization of its casino sector. This growth has been enabled by massive influxes of foreign capital and migrant labor that have dramatically altered the city’s ethnic landscape. In this paper, the author examines the demographic changes Macao has experienced as a result of the casino boom, and situates the city’s current economic growth and ethnic diversification within its long history as a multi-ethnic city.

Design/methodology/approach

Building on Nancy Foner’s notion of “contexts of settlement,” the study draws on census materials, policy statements, newspaper articles and ethnographic materials to examine how changing ideologies of globalization help shape the categories through which ethnic diversity itself is conceptualized.

Findings

The paper has three main findings. First, despite the Macao government’s multicultural rhetoric, its labor and residency policies that prevent migrant workers from settling in Macao may paradoxically serve to maintain the ethnic status quo ante. Second, the new contexts of settlement engendered by Macao’s casino globalization may be amplifying fissures within the ethnic category “Chinese.” And third, discourses of globalization, regulations on immigration, and classificatory systems governing ethnic diversity that were instituted under Portuguese rule have both helped shape these new contexts and been reworked in the process.

Originality/value

As the processes of urbanization, economic integration and transnational migration continue to accelerate throughout East Asia, the goal of creating inclusive, equitable multi-ethnic urban societies will require closer examination of the relationship between particular modes and ideologies of “global” engagement, patterns of and policies toward migration and the concepts and categories through which diversity is measured. This approach to understanding multi-ethnic Macao may serve as an example.

Details

Social Transformations in Chinese Societies, vol. 15 no. 2
Type: Research Article
ISSN: 1871-2673

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