超临界流体Rayleigh-Bénard对流的数值模拟研究

Numerical Study of Rayleigh-Benard Convection in a Supercritical Fluid

物质气液临界点附近热物理性质发生剧烈变化,会出现一种对热力学平衡有显著加速作用的热声活塞效应。而在长时间尺度上,因重力作用而产生的Rayleigh-Bénard对流在活塞效应的影响下,其表现出来的物理特性与普通流体相比存在较大的差异。我们通过SIMPLE方法对超临界氮在不同临界距离下的自然对流发生过程进行数值模拟,结果显示当流体热力学状态接近临界点时,对流作用的发生取决于边界层内热羽流的形成,并且具有明显的湍流特征,而随着离开临界点的距离加大,流场的形成逐渐过渡到一般可压缩流体的情形。

Dramatic changes are expected of thermophysical properties near the liquid-gas critical point,which gives rise to the piston effect that accelerates thermal equilibration.On a long timescale, the gravity-induced Rayleigh-Benard convection,influenced by the piston effect,exhibits features different from normal fluids.By the use of the SIMPLE algorithm,we study the evolution of convection in supercritical nitrogen at different proximities to the critical point.The results show that fluid motion is dominated by turbulent thermal plumes extremely close to the critical point.As the distance to the critical point grows,the formation of the flow pattern resembles that of a weakly compressible fluid.