2d natural convection

hello everybody,

im trying to simulate an inductive heating of a cylinder, my problem is that i cant add the natural convection (between air and the cylinder) i've tried to add an outflow BC but i cant add any boudary. i have air all around the cylinder and the inductor, its a 2d axisymetric geometry. please if anyone could help it'll be great.

Thanks,
Achraf.