Abstract: The instability in the natural convection boundary layer initiates with the buoyancy eigenmode and develops into non-linear stage with the turbulization of the buoyancy eigenmode. In the mean time, the invisid eigenmode at the inflexion point appears and begins to increase at the outer layer. Experimental results show that the turbulent layer near the maximum velocity point can be detected while the reformed Grashof number G＞100 and after the buoyancy eigenmode crashes down; when G＞170, the invisid eigenmode becomes turbulent and the viscous eigenmode in the high shear layer near the wall appears. All of these characterize the growth and decaying of the instability waves in the natural convection boundary layer with spatial mode.

Key words: buoyancy instability, invisid instability, viscous instability, neutral curve, eigenmode

摘要： 自然对流边界层的稳定性由浮力振型失稳开始，并随着浮力振型的湍流化进入非线性阶段，与此同时，无粘性振型在外层开始失稳。实验结果表明，修正格拉斯霍夫数(Grashof) G＞100时，浮力振型破碎并在最大速度点附近形成湍流层；当G＞170时，外层无粘性振型湍流化而近壁层的粘性不稳定性开始失稳，形成中层-外层-内层三种流动不稳定机制此消彼长的发展过程。

关键词: 浮力不稳定性, 无粘性不稳定性, 粘性不稳定性, 中性曲线, 特征振型