A numerical study of free convective heat transfer within domed skylight cavities

Domed skylights are important architectural design elements to deliver daylight and solar heat into buildings and connect buildings' occupants to outdoors. To increase the energy efficiency of skylighted buildings, domed skylights employ a number of glazing layers forming enclosed spaces. The latter are subject to complex buoyancy-induced convection heat transfer. Currently, existing fenestration design computer tools and building energy simulation programs do not, however, cover such skylights to quantify their energy performance when installed in buildings. his work presents a numerical study on natural laminar convection within concentric and vertically eccentric domed cavities. The edges of domed cavities are assumed adiabatic and the temperature of the interior and exterior surfaces are uniform and constant. The concentric and vertically eccentric domed cavities were studied when heated from inside and heated from outside, respectively. A commercial CFD package employing the control volume approach is used to solve the laminar convective heat transfer within the cavity. The obtained results showed steady flow for small Grashof numbers. For moderate and large Grashof numbers, depending on the gap ratio and the cases of heating from inside or outside, the flow may be steady or transient periodic with a single vortex-cell or multi vortex-cells. The Nusselt number for the case of heated from inside is greater than the case of heated from outside. The numerical results show that the changes in the gap ratio have smaller effect on Nusselt number in high profile domed skylights than lower profile domed skylights.

A numerical study of free convective heat transfer within domed skylight cavities

Domed skylights are important architectural design elements to deliver daylight and solar heat into buildings and connect buildings' occupants to outdoors. To increase the energy efficiency of skylighted buildings, domed skylights employ a number of glazing layers forming enclosed spaces. The latter are subject to complex buoyancy-induced convection heat transfer. Currently, existing fenestration design computer tools and building energy simulation programs do not, however, cover such skylights to quantify their energy performance when installed in buildings. his work presents a numerical study on natural laminar convection within concentric and vertically eccentric domed cavities. The edges of domed cavities are assumed adiabatic and the temperature of the interior and exterior surfaces are uniform and constant. The concentric and vertically eccentric domed cavities were studied when heated from inside and heated from outside, respectively. A commercial CFD package employing the control volume approach is used to solve the laminar convective heat transfer within the cavity. The obtained results showed steady flow for small Grashof numbers. For moderate and large Grashof numbers, depending on the gap ratio and the cases of heating from inside or outside, the flow may be steady or transient periodic with a single vortex-cell or multi vortex-cells. The Nusselt number for the case of heated from inside is greater than the case of heated from outside. The numerical results show that the changes in the gap ratio have smaller effect on Nusselt number in high profile domed skylights than lower profile domed skylights.

3D Simulation of Flow in a Vortex Cell Using RANS and Hybrid RANS-LES Turbulence Models

A vortex cell is a cylindrical aerodynamic cavity that traps separated vortices to prevent the formation of large-scale vortex shedding. Due to the presence of complex vortical structures, regions with varying turbulent intensities, and rotation-curvature effects on turbulent structure; the flow inside a vortex cell is a valuable test case for newly proposed turbulence models and numerical schemes. In the present study, numerical simulations were carried using a Reynolds-averaged Navier-Stokes (RANS) turbulence model and two hybrid RANS/large-eddy-simulation (LES) models. The computational domain consists of a cylindrical cavity with an incoming transitional boundary layer and a Reynolds number of 9.4 × 104 based on the diameter of the cavity. Results indicate that the RANS model provides general information about the flow characteristics, while the hybrid RANS-LES models predict the flow characteristics with more accuracy but suffer inaccuracies due to the details of the RANS to LES transition. Most significantly, the dynamic hybrid RANS-LES (DHRL) model in combination with a low-dissipation numerical scheme overpredicts the turbulent mixing in the vortex cell and fails to provide an accurate representation of the physics of the trapped vortex. It is concluded that the hybrid RANS-LES models used in this study need further work to be able to fully and accurately predict the flow in a vortex cell.

Overview of Coănda Jet and Vortex Cell Circulation Control

Flow control for enhanced aerodynamic performance have been utilized for enhanced lift, reduced drag and delay of stall at higher angle of attack. To this end, techniques such as continuous, synthetic and pulsed jets, compliant surface, vortex-cell, Coănda jet and the like have been developed and applied to alter the behavior of airfoils, wings, and bodies and other aerodynamic components. Two such techniques are here assessed as potentially promising technique in the framework of airfoil surface blowing circulation enhancement, i.e. Coănda-jet circulation enhancement and vortex-cell. Their progress and development in influencing the effectiveness and configuration of airfoil surface blowing for circulation enhancement of aerodynamic surfaces are discussed, using fundamental principles and CFD technique.