Flow Field and Reynolds Stress Distribution in Low Turbulence Natural Convection in a Triangular Cavity

Talabi, S.O.; Olunloyo, V. O. S.; Kamiyo, O. M.; Collins, Michael W.; Karayiannis, Tassos G.

doi:10.1615/ichmt.2006.turbulheatmasstransf.1060

Cited by 7 publications

(8 citation statements)

References 16 publications

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“…Although the geometry and boundary conditions are symmetric about x = 0, the predicted air flows in the sealed attics are asymmetric, independent of the roof pitch variation. The asymmetric flow pattern found here is consistent with the previous numerical studies (e.g., [17,18,22]) and the experimental results of Holtzman et al [10]. In this flow visualization experiment, smoke was slowly injected into an air-filled triangular enclosure, which was constructed of aluminum plates with milled passageways for circulating fluid to maintain isothermal surfaces and to impose a temperature difference between the base and upper walls.…”

Section: Sealed Atticssupporting

confidence: 90%

“…Although the air flow in real residential attics is almost always turbulent, a considerable number of experimental and numerical studies have been devoted to the analysis of flow and heat transfer under laminar conditions (e.g., [7][8][9][10][11][12][13][14][15][16]), and only a few studies investigated turbulent flow and heat transfer in sealed attics. For example, Ridouane et al [17] employed a low-Reynolds-number k-ε model to simulate the turbulent natural convection in an air-filled isosceles triangular enclosure representing attic spaces under winter conditions, and Talabi et al [18] numerically investigated the turbulent natural convections in sealed attics under both summer and winter conditions using the Reynolds stress turbulence model and considering both isothermal and isoflux boundary conditions. Air flow and heat transfer in vented attic spaces have been scarcely investigated in the past.…”

Section: Introductionmentioning

confidence: 99%

“…A major difference from [22] is that an unsteady numerical formulation is adopted in this study, because the steady model could not produce convergent solutions for some cases with roof pitches higher than 8/12, even after carefully adjusting the various under-relaxation factors. Unsteady RANS (URANS) modeling has been shown to be an effective approach to overcome numerical stiffness and improve solution convergence in previous studies for natural convection flows in enclosures [18,[29][30][31][32]. Such an approach is also a recommended strategy in commercial CFD manuals [33] for solving natural convection problems.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Wang¹,

Shen²

2012

Sustainability

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Pitch value is an important consideration in residential gable roof design and construction. However, how roof pitch, coupled with air flows in attic space, affects the energy performance of building attics has been barely investigated. In this paper, a 2D unsteady computational fluid dynamics (CFD) model is employed to investigate the effects of roof pitch on air flow and heating load of both sealed and vented attics for gable-roof residential buildings. The simulation results show that air flow in the sealed attics is steady and asymmetric, while that in the vented attics is a combination of an essentially symmetric base flow and a periodically oscillating flow. For both the sealed and vented attic cases, the heating load is found to increase with the roof pitch, and the heat transfer of turbulent air flow in attic space can be satisfactorily correlated by a simple relationship between appropriately defined Nusselt number and Rayleigh number.

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Section: Sealed Atticssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Wang¹,

Shen²

2012

Sustainability

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“…In the first category, sealed attic configuration is considered, and the problem is usually represented by natural convection in triangular enclosures. As reviewed by Kamiyo et al [5] and by Saha and Khan [6], a considerable number of experimental and numerical studies in this category (e.g., [7][8][9][10][11][12][13][14][15][16]) have been devoted to the analysis of flow and heat transfer under laminar conditions, while only a few studies (e.g., [17,18]) investigated turbulent flow and heat transfer, although the air flow in real residential attics is almost always turbulent.…”

Section: Introductionmentioning

confidence: 99%

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

Wang

Shen

2012

Energies

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Abstract:The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD) model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for typical summer conditions. Ventilation ratios from 1/400 to 1/25 combined with both balanced and unbalanced vent configurations are investigated. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the variations in ventilation ratio and vent configuration. The predicted temperature fields are characterized by thermal stratification, except for the soffit regions. It is demonstrated that an increase in ventilation ratio will reduce attic cooling load. Compared with unbalanced vent configurations, balanced attic ventilation is shown to be the optimal solution in both maximizing ventilating flow rate and minimizing cooling load for attics with ventilation ratio lower than 1/100. For attics with ventilation ratios greater than 1/67, a configuration of large ridge vent with small soffit vent favors ventilating air flow enhancement, while a configuration of small ridge vent with large soffit vent results in the lowest cooling energy consumption.

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“…An unsteady numerical formulation is adopted in the study, as the steady solutions could not always converge, even after carefully adjusting the various under-relaxation factors. Unsteady Reynolds-averaged Navier-Stokes (URANS) modeling has been shown to be an effective approach to overcome numerical stiffness and improve solution convergence in previous studies for natural convection flows in enclosures [13][14][15][16][17]. The URANS approach is also a recommended strategy in commercial CFD manuals [18] for solving natural convection problems.…”

Section: Introductionmentioning

confidence: 99%

The Impact of Roof Pitch and Ceiling Insulation on Cooling Load of Naturally-Ventilated Attics

Wang

Shen

2012

Energies

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A 2D unsteady computational fluid dynamics (CFD) model is employed to simulate buoyancy-driven turbulent ventilation in attics with different pitch values and ceiling insulation levels under summer conditions. The impacts of roof pitch and ceiling insulation on the cooling load of gable-roof residential buildings are investigated based on the simulation of turbulent air flow and natural convection heat transfer in attic spaces with roof pitches from 3/12 to 18/12 combined with ceiling insulation levels from R-1.2 to R-40. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the investigated variations of roof pitch and ceiling insulation. Furthermore, it is predicted that the ceiling insulation plays a control role on the attic cooling load and that an increase of roof pitch from 3/12 to 8/12 results in a decrease in the cooling load by around 9% in the investigated cases. The results suggest that the increase of roof pitch alone, without changing other design parameters, has limited impact on attics cooling load and airflow pattern. The research results also suggest both the predicted ventilating mass flow rate and attic cooling load can be satisfactorily correlated by simple relationships in terms of appropriately defined Rayleigh and Nusselt numbers.

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Flow Field and Reynolds Stress Distribution in Low Turbulence Natural Convection in a Triangular Cavity

Cited by 7 publications

References 16 publications

Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Effects of Roof Pitch on Air Flow and Heating Load of Sealed and Vented Attics for Gable-Roof Residential Buildings

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

The Impact of Roof Pitch and Ceiling Insulation on Cooling Load of Naturally-Ventilated Attics

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