Effect of gas radiation-depended natural convection on the transition of spatially developing boundary layers

In this study, the effect of natural convection affected by gas radiation on a spatially developing boundary layer was investigated through large-eddy simulations to evaluate the interaction between natural convection and thermal radiation in an open environment, wherein Tollmien–Schlichting instabilities dominate. The gas radiation was calculated using the discrete ordinate method considering gray gas as the medium, and the effect of the absorption coefficient of the medium on the boundary layer has been discussed. With gray gas medium with small and large absorption coefficient values, a turbulent boundary layer was observed, while with intermediate absorption coefficient values, little turbulence was observed. As the gas heated due to radiation, the thermal boundary layer thickness increased. With the thickening of the thermal boundary layer, the magnitude of the velocity gradient at the inflection point decreased, stabilizing the flow and damping the thermal boundary layer fluctuations owing to the Tollmien–Schlichting mechanism. The transition to turbulence of the boundary layer could be reduced when the fluid far from the heated wall was heated through thermal radiation and the shear stress at the infection point decreased. These results provide insights for the control of turbulence for natural convection.