Dear Mr. Kambiz Thank you for your reply. I need some more information on periodic boundary conditions. I am simulating Rayleigh-Benard convection where a viscous fluid is heated between two infinite horizontal rigid plates. The bottom plate is heated. When the temperature difference between the two horizontal plates which is quantified by the Rayleigh number exceeds a certain critical value(1708) convection sets in and hot fluid from the bottom ascends in the middle of the cell and descends as cooler fluid on the lateral sides of the cell. When I mean cell I am referring to periodic cells which form between the plates for the entire horizontal length. So there will be one cell for a horizontal length of 2.016. My question is since there are no rigid lateral boundaries I have to use periodic boundary conditions. So how should I implement the velocity, temperature and pressure on the two lateral periodic boundaries. Are periodic boundaries different from symmetrical boundaries? I am using a staggered grid.

With regards Suresh

Symmetry BC means the normal fluxes at the boundary are 0. Periodic BC means that what goes out at one end enters in at the other end at the matching location.

Dear Rami, Thanks a lot for your answer on Periodic BC. It was very useful to me.

Suresh