Effect of surface radiation on the breakdown of steady natural convection flows in a square, air-filled cavity containing a centered inner body

► Heat transfer in cavities cooled from below and above with an inner heated body. ► Effects of radiation on the transitions to unsteady flows are numerically studied. ► The surfaces are gray and diffuse and the temperature differences are from 1 K to 5 K. ► Critical Rayleigh numbers are considerably increased by radiation. ► According to the thermal boundary conditions, combined analyses are required.