关键词: 浮力不稳定性, 中性曲线, 涡量波, 特征振型

Abstract: An experimental investigation on the buoyancy instability in the natural convection boundary layer is presented, including its basic characteristics such as power spectrum, wavelength, phase velocity and related critical layers, and its developing process of growth and dissipation with the variation of Grash of number. Results indicate that the natural convection boundary layer becomes unstable due to buoyancy at a critical modified Grashof number G around 40; the neutral curve obtained by the growth rates of the temperature fluctuation has a ring-like curve separated from the main branch of Nachtsheim's calculation by velocity fluctuation at the lower Grashof number side; and its phase velocity is close to the maximum mean velocity where the critical layer of the eigenmode locates. The thermal fluctuation decays rapidly as the non-dimensional frequency above 0.4, so that it means that the coupling effect between instability wave generated by buoyancy fluctuation and velocity waves by invicid instability seems weak enough for their critical layers in the range of the non-dimensional frequency B＜0.4.

Key words: buoyancy instability, neutral curve, vortex wave, eigenmode