Numerical simulation of turbulent natural convection around spheres
Published 2020-10-27
Keywords
- heat transfer,
- natural convection,
- boundary layer,
- laminar zone,
- turbulent zone
- transition,
- Rayleigh number,
- Nusselt number,
- sphere,
- laminar model,
- turbulence model,
- k-ε model,
- Ansys Fluent ...More
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Abstract
Most of the research that has been done on natural convection has focused its study on the laminar region and not much attention has been focused on the turbulent natural convection, that usually occurs when the Rayleigh number exceeds a certain critical value. Recent studies have shown that the correlations identified for this region are often imprecise. On the other hand, the numerical treatment of this problem presents difficulties related to the turbulence model used, since it is in the presence of a laminar-turbulent boundary layer in a laminar environment, therefore, the laminar model will underestimate the heat transfer, while the turbulent models will overestimate it. Transitional models and other options are available but are designed for turbulent environments. The present work proposes the numerical solution using the Ansys Fluent computer program of turbulent laminar convection around spheres without a turbulence model (laminar model) and using a k-ε turbulence model for low Reynolds numbers. The work should characterize the Rayleigh numbers from which the change from boundary layer to turbulent begins to change, as well as the position of the boundary layer detachment. The values obtained for the heat transfer with the laminar model showed very good agreement with experiments and correlations for low Rayleigh numbers, but lost precision from a certain Rayleigh value, an aspect that could be successfully corrected by incorporating the used turbulence model.
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References
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