The stability limit of longitudinal roll cells in a flowing glass steadily cooled by radiation is investigated using an unsteady SIMPLER code with a periodic boundary condition. The P1 approximation is used for analysis of the radiative heat transfer: The upper surface is subject to radiative cooling and the rigid bottom is insulated. This study is focused on the occurrence of longitudinal roll cells aside from the overall back flow. The critical Rayleigh number and associated wavenumber are obtained as a function of the Prandtl number, dimensionless mass flow rate, optical thickness, emissivity of the bottom wall and environmental temperature. The flow is destabilised with decreasing the Prandtl number, increasing the dimensionless mass flow rate, increasing the optical depth and increasing the environmental temperature.
