竖直恒温面自然对流边界层不稳定性研究

Instability of natural convection boundary layer and resonance enhanced heat transfer adjacent to an vertical isothermally heated surface

在无扰动、随机式扰动以及正弦式扰动下,通过对竖直恒温面处状态Ra为1.328×10^9、Pr为6.24的自然对流进行模拟,探索了热边界层的不稳定性和共振强化自然对流换热。结果表明:(1)竖直自然对流边界层上游位置的随机式扰动对热边界层的影响主要体现在稳定阶段;(2)该状态下的竖直自然对流边界层的特征频率为15 067,且相比于无扰动状态,频率为15 067的正弦式扰动能在竖直恒温面处提高5.15%的换热量;(3)在竖直自然对流边界层上游位置加入特征频率的正弦式扰动,竖直恒温面处的局部努塞尔数Nu均出现明显波动,且波动随着边界层高度的增加而增大。

By simulating the natural convection with Ra of 1.328×10^9, Pr of 6.24 at the vertical isothermal surface without disturbance, random disturbance and sinusoidal disturbance, the instability of natural convection boundary layer and resonance enhanced heat transfer were explored.The results show that:(1)the influence of random perturbation of the upstream position of the vertical natural convective boundary layer on the thermal boundary layer is mainly reflected in the stable stage;(2)The characteristic frequency of the vertical natural convective boundary layer in this state is 15 067, and compared with the undisturbed state, the sinusoidal disturbance with frequency of 15 067 can improve the heat exchange of the vertical constant temperature surface by 5.15%;(3)By adding sinusoidal perturbation with characteristic frequency to the upstream position of the vertical natural convective boundary layer, the local Nusselt number at the vertical isothermal surface fluctuates obviously, and the fluctuation increases with the increase of the height of the boundary layer.