Numerical simulation of Rayleigh-Bénard convection of nanofluids in rectangular cavities

In order to understand the characteristics of Rayleigh-Bénard convection of nanofluids in a rectangular cavity, a series of threedimensional numerical simulations were carried out by using the finite volume method. The working mediums were Al2O3-water and CuO-water nanofluids, and Rayleigh number varied from 1708 to 1.5×105. Results show that the critical Rayleigh number of the Rayleigh-Bénard convection onset increases with the increase of the volume fraction of nanoparticles, which hints that nanoparticles make the flow become more stable. Furthermore, the critical Rayleigh number decreases with the increase of the aspect ratio of the cavity. After convection appears, the average Nusselt number at the bottom wall increases, but the flow intensity and the oscillation frequency decrease with the increase of the volume fraction of nanoparticles. With the increase of Rayleigh number, there exist four bifurcation sequences, which are Steady flow (SF) → Periodic oscillatory flow (POF) → Chaotic flow (CF), SF → POF → SF → POF →CF, SF → POF → Multiple periodic oscillatory flow (MPOF) → POF →CF and SF → POF → MPOF →CF.