湍流边界层逆转捩机制的实验研究

实验研究了板面向下的平板边界层中的逆转捩现象，测量了加热前后湍能生成项，耗散项和吸收项的变化规律，初步解释了逆转捩发生的物理机制。实验结果表明，通过加热，形成稳定的密度分层结构，在距离平板前缘 400—1000 mm 范围内，湍能生成项变为负值，成为实际上的湍能集中吸收区，使得边界层内层的湍流能量被迅速吸收；近壁区的小尺度涡对于湍能的耗散作用进一步增强；同时浮力引起的湍能吸收项对湍能输运也起到了很好的抑制作用。外层流动失去了能量来源，从而使得流动逐渐从湍流演变为层流。

Experimental Research on the Mechanism of Reverse Transition in Turbulent Boundary Layer

Experimental research on the phenomenon of reverse transition in the boundary layer under a heated plate is presented, and the mechanism of reverse transition is also explained. During the experiment, the production term, dissipation term as well as absorption term of turbulent energy is measured. Experimental results show that, through the formation of stably stratified structure, the production term of turbulent energy in the range between 400-1 000 mm away from the leading edge of the plate has become negative, so the region is actually an absorption region of turbulent energy. In the same time, the dissipation term near the wall region is strengthened by small-scale eddy, Under the conjunct effect of the negative production term, the absorption term, as well as the absorption term caused by buoyancy, the turbulent energy in the inner layer of turbulent boundary layer is depleted rapidly, and the turbulent flow in the outer layer changes into passive flow because of the lack of energy source. Finally, the turbulence turns into laminar flow.