How can we provide boundary condition at a boundary which act as both inlet & outlet?
 

Hi,
iI am modelling a downward facing cavity. how should i provide the boundary condition at the bottom surface which act as both inlet and outlet of air.?:)

you can choose either pressure inlet or pressure outlet. Both these boundary conditions would take care of reverse flow. For eg. if you choose boundary as pressure outlet, in case of reverse flow, it would behave as a pressure inlet.