底部加热长方体腔内自然对流的非线性特性

Nonlinear Characters of Natural Convection Heated From Below

采用SIMPLE算法,QUICK差分格式,对底部加热三维长方体腔内空气的自然对流进行了数值模拟。根据模拟结果,探讨了方腔内流体流动与换热的静态分岔与振荡等非线性现象。数值结果显示,在固定的几何尺寸和不同Ra的情况下,当初始场不同时,会出现若干不同的解,即存在解的静态分岔;在固定的几何尺寸和相同的初始场情况下,低Ra时流动和换热处于稳态,当Ra超过某一临界值时,流动和换热就会随时间振荡,并通过倍周期分岔过渡到混沌;当方腔的几何尺寸不同时,分岔点的特征值Ra也发生变化。

Nonlinear phenomena in natural convection of air in a three-dimensional rectangular cavity heated from below have been investigated numerically using SIMPLE algorithm with QUICK scheme. It is found that the different results occur when the different initial conditions are given and only one of the results is consist with the experimental result. But the influence of initial conditions appears in some range. When Rayleigh number is above a critical value, unsteady oscillation occurs. With increase of Rayleigh number, flow and heat transfer change from steady to unsteady state, and transition to chaos occurs through multi-periodical oscillation. The critical value of Rayleigh number of transition is different for different aspect ratio.