Large Eddy simulation of tracer gas dispersion in a cavity

McMullan, W. A.

doi:10.1088/1873-7005/ac421b

Cited by 4 publications

(6 citation statements)

References 53 publications

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“…The LES results reported here are performed using the OpenFOAM v2112 solver suite (www.openfoam.com). The open-source CFD software suite has been used extensively in the study of urban environment flows (Jeanjean et al 2015, Zhong et al 2015, García-Sánchez et al 2018, Kikumoto and Ooka 2018, McMullan 2022, McMullan and Angelino 2022. The filtered variables are stored on a collocated grid, and the governing equations are solved using a PIMPLE algorithm.…”

Section: Methodsmentioning

confidence: 99%

“…Many such models exist in the literature, with the Smagorinsky model (Smagorinsky 1963), the WALE model (Nicoud and Ducros 1999), and the Germano-Lilly model (Germano et al 1991, Lilly 1992, being the most commonly used for USC/cavity flows (Tominaga et al 2008, Cheng and Liu 2011, Kikumoto and Ooka 2018. LES has been extensively used to simulate cavity-type flows at isothermal conditions (Li et al 2009, Han et al 2018, Kikumoto and Ooka 2018, McMullan 2022, where it has been shown that the vortex structure within the cavity is captured using LES (Cui et al 2004), and that the aspect ratio of the cavity plays a key role in the topology of the vortex structure within it (Li et al 2008). LES studies of the cavity-type flow at thermally stratified conditions are less common in the literature, with both unstable stratification conditions (Li et al 2010, Park et al 2012, and stable stratification conditions considered (Li et al 2015(Li et al , 2016.…”

Section: Introductionmentioning

confidence: 99%

“…In this research, the effects of thermal stratification on the dispersion of tracer gas within a simulated laboratory-scale cavity are studied. The numerical simulations are based on the isothermal experiments of Kikumoto and Ooka (2018), and a validated OpenFOAM LES method is used to perform the simulations (McMullan 2022). The effects of thermal stratification are assessed through the heating of walls within the cavity to produce unstable stratification, or cooling of the walls within the cavity to produce stable stratification.…”

Section: Introductionmentioning

confidence: 99%

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Large eddy simulation of thermal stratification effects on tracer gas dispersion in a cavity

McMullan,

Mifsud

2023

Fluid Dyn. Res.

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This paper assesses the effect of thermal stratification on the prediction of inert tracer gas dispersion within a cavity of height (H) 1.0 m, and unity aspect ratio, using large eddy simulation. The Reynolds number of the cavity flow, was 67 000. Thermal stratification was achieved through the heating or cooling of one or more of the walls within the cavity. When compared to an isothermal (neutral) case, unstable stratification from surface heating generally has a weak influence on the primary recirculating cavity vortex, except in the case where the windward wall is heated. For windward wall heating, a large secondary vortex appears at the corner of the windward wall and cavity floor. Unstable stratification has no significant influence on the removal of pollutant mass from the cavity. Stable stratification through surface cooling drastically alters the flow pattern within the cavity, pushing the cavity vortex towards the upper quadrant of the cavity. As a result, large regions of stagnant fluid are present within the cavity, reducing the effectiveness of the shear layer at removing pollutant concentration from the cavity. Some stable stratification configurations can increase the pollutant mass within the cavity by over a factor of five, when compared to the neutral case. Pollutant concentration flux maps show that, in stably stratified cases, the majority of pollutant transport from the cavity is the result of entrainment into the primary cavity vortex. The results show that pollutant concentrations in urban street canyon-type flows are substantially altered by diurnal heating and cooling, which may influence pedestrian management strategies in urban environments.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Large eddy simulation of thermal stratification effects on tracer gas dispersion in a cavity

McMullan,

Mifsud

2023

Fluid Dyn. Res.

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“…They found that the heated windward wall could cause a multi-vortex structure within the canyon. When the walls are cooled, the evolution of the shear layer is delayed, leading to stagnant flow in the bottom part of the canyon [49]. Chew et al compared the RANS and LES at reduced and full scales.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of local and upwind temperature stratification on flow and dispersion in a bi-dimensional street canyon

Huang,

Gao

2024

PLoS ONE

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The thermal effect mainly includes boundary temperature stratification and the local thermal effect. The combined effect of these factors on flow and dispersion in a bi-dimensional canyon was investigated by the RANS and LES methods to evaluate their performance. The results, including the flow field, turbulent kinetic energy, temperature, heat flux, pollutant concentration and fluxes, were compared with the data from wind tunnel experiments. The comparison results showed that the RANS method severely overestimated the impact of windward heating on the flow in the canyon because of the lack of simulated flow separation ability and the limitation of the Boussinesq model, leading to an incorrect flow field and an incorrect temperature and concentration. In contrast, LES performed better mainly because of its ability to simulate flow separation. LES regenerated the right vortexes, flow field and low wind velocity. LES slightly overestimates the overall temperature in the canyon because heat exchange is eliminated in LES but difficult to avoid in the experiment. The difference in the air exchange rate at the roof level between the LES and wind tunnel data was no more than 5%, and the pollutant concentration distribution of the LES was almost the same as that of the experiments. This work emphasizes that the RANS method has limited ability to simulate flow and dispersion when the thermal effect is considered even at a reduced-scale, while LES can simulate the combined effects of incoming flow temperature stratification and local thermal effects. It is therefore suggested that if computing resources are limited and the temperature difference is not large, a steady-state calculation RANS can be used. Otherwise, LES must be performed.

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“…The LES method can effectively obtain the real transient flow field information, and can be used to predict complex flows such as separation and transition. And the LES framework has been widely used in the study of ventilated cavity flows (Hughes et al 2001, Yu et al 2020, Shen et al 2022, McMullan 2022, and good results have been obtained. In this study, there are obvious entrainment and shedding phenomena in the ventilated cavity, in order to better obtain the internal flow field information, the LES turbulence model is used in this paper.…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical study on unsteady entrainment behaviour of ventilated air mass in underwater vehicles

Qu,

Yang,

Yao

et al. 2023

Fluid Dyn. Res.

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The hydrodynamic characteristics of underwater vehicles are significantly affected by the ventilated cavity covered by the vehicle surface. In this paper, the unsteady flow characteristics of this ventilated cavity are studied using experimental and numerical methods, and the unsteady entrainment behaviour of the ventilated air mass is emphasised. The flow pattern of the ventilated air mass is recorded using a high-speed camera. The large eddy simulation turbulence model is employed for the numerical simulations, and a good agreement is observed between the experimental and numerical results. In the early stage of the formation of the ventilated air mass, the internal structure exhibits a symmetric kidney vortex system, while the ventilated cavity below the vent hole has a continuous hairpin vortex structure. The ventilated air mass experiences a growth stage, an entrainment stage, and a shedding stage. The entrainment behaviour enables the ventilated air mass to quickly fill the ventilated cavity and modifies the surface pressure distribution of the vehicle. As the cavitation number decreases, the radial size of the ventilated cavity increases, and the contact area between the cavity and the water body increases, thus enhancing the vertical drag coefficient of the vehicle.

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Large Eddy simulation of tracer gas dispersion in a cavity

Cited by 4 publications

References 53 publications

Large eddy simulation of thermal stratification effects on tracer gas dispersion in a cavity

Large eddy simulation of thermal stratification effects on tracer gas dispersion in a cavity

Numerical simulation of local and upwind temperature stratification on flow and dispersion in a bi-dimensional street canyon

Experimental and numerical study on unsteady entrainment behaviour of ventilated air mass in underwater vehicles

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