滑移边界对二维Rayleigh-Bénard热对流流态和传热特性的影响

采用并行直接数值模拟（PDM-DNS）计算无滑移和滑移边界二维Rayleigh-Bénard热对流.与无滑移边界形成的随机羽流运动的湍流热对流不同，滑移边界热对流最终形成湍流特征消失，且温度仅分布于四壁的一个大尺度环流的流动形态.平均场近底板的温度分布特性，无滑移边界逐渐变化而滑移边界出现过冲现象.宽高比Γ=1时，Nusselt数（Nu）随Rayleigh数（Ra）的变化具有相同标度指数，Nu~Ra^0.3.滑移边界热对流具有传热增强作用.滑移边界热对流Nu随Γ变化明显，并分为两个阶段，在Γ=0.5时出现Nu_max≈250，是无滑移边界热流Nu的5倍.

Effect of Free-slip Boundaries on Flow and Heat Transport Characteristics in Two-dimensional Rayleigh-Bénard Convection

Temperature fields in two-dimensional (2D) Rayleigh-Bénard (RB) convection with no-slip and free-slip walls were simulated with parallel direct method of direct numerical simulation (PDM-DNS) at different Rayleigh numbers (Ra) and aspect ratio numbers (Γ). Different from no-slip boundary thermal convection with random plume, free-slip boundary thermal convection eventually forms a large-scale circulation without turbulent features and temperature distributes only on four walls. Temperature distribution characteristics of time-average field near floor changes gradually for no-slip boundary but overshoot occurs for free-slip boundary. Dependences of Nusselt numbers (Nu) with Ra at Γ=1 have same scale index Nu~Ra^0.3. Free-slip boundary thermal convection enhances heat transfer. Changes of Nu with Γ are obvious in free-slip boundary thermal convection. They are in two stages. At Γ=0.5, Nu_max≈250, it is five times of Nu in no-slip boundary thermal convection.