Natural convection in a square cavity with two different distributions of sinusoidal vertical wall temperature is studied numerically. Existence of periodic or non-periodic phenomena characterized by fluctuations in flow field and heat transfer is examined for both wall temperature distributions with various Rayleigh numbers. Computational analysis with the projection method involving a Godunov-type discretization for convective terms is also carried out to investigate the effect of Prandtl numbers on heat transfer characteristics and flow regimes. It is demonstrated that the type of the location of heating and cooling zones plays significant role on the flow pattern in the enclosure