Three-dimensional numerical study of natural convection in an inclined porous cavity with time sinusoidal oscillating boundary conditions

摘要

Three-dimensional unsteady natural convections in an inclined porous cavity with time oscillating boundary conditions are numerically studied in this paper. The Darcy-Forchheimer-Brinkman model is adopted to model the fluid flow in the porous medium and the combination effects of inclination angles (α_1, α_2) and temperature oscillation frequency (f) on the convection characteristics with different Ray-leigh numbers (Ra = 10~6 and 10~7) are carefully investigated, especially when the porous cavity is seriously inclined (80° ≤ α_1 ≤ 90°). It is revealed that, when the porous cavity is moderately inclined (0° ≤ α_1 ≤ 75°, α_2 = 0°), the natural convections inside are stable and quasi two-dimensional. However, if the cavity is seriously inclined (75° ≤ α_1 ≤ 90°, α_2 = 0°), the flow patterns inside are much more complicated and the three-dimensional multiple roll-cells with different intercrossing angles are established. It is also found that, when the porous cavity is inclined with three-dimensional method (α_1 > 0°, α_2 > 0°), the natural convections become quite different and a series of three-dimensional screw type flexural roll-cells appears. Furthermore, it is suggested that, with proper selection of inclination angles and oscillation frequency, the natural convection heat transfer will be significantly improved and the maximal heat fluxes are finally obtained at the optimal combinations of f= 35π, α_1 = 50°, α_2 = 45° when Ra = 10~6 and f= 40π, α_1 = 45°, α_2 = 45° when Ra = 10~7.