A series of numerical simulations on natural convection of water near its density maximum in a cavity with complex geometry structure was performed using finite volume method. The flow and thermal fields and the variation law of local and average Nusselt on the wall with the Rayleigh number at different density inversion parameters were obtained. The results show that the effect of density inversion parameter on the flow structure and heat transfer characteristic is significant. The flow intensity becomes weak with the increase of the aspect ratio. Under the same conditions

the flow

thermal fields and heat transfer rates vary in degree with the geometry structure of the out wall changes.