加热平板表面温度分层产生的湍流逆转捩现象

针对加热平板表面密度分层结构中的逆转捩现象，在二元风洞中进行了系统的实验研究。对局部加热的水平平板下表面边界层内的时均速度的演化规律进行了详细的测量，同时对速度脉动信号以及速度能谱进行了分析，并对边界层内的波动特性进行了研究。这些参数体现了边界层逆转捩过程中流动特性的变化规律，揭示了密度分层结构中逆转捩现象发生的机制。在实验中对比了局部加热平板表面的边界层与无温度梯度情况下自然形成的湍流边界层的特性。发现在加热的情况下，边界层的形状因子由1.5上升至2.6；时均速度廓线中的平衡湍流层消失；以及速度能谱中惯性子区消失等变化。在实验中还发现加热平板表面速度信号中出现了间歇现象。实验结果表明板面附近的流动已由湍流流动转变为层流流动，同时平板表面的摩擦系数较没有温度梯度时有大幅度下降，不仅证明了边界层逆转捩现象的存在，也说明了这种条件起到了减阻的效果。

Phenomenon of Reverse Transition on a Heated Flat Plane with Stable Temperature Stratification

In the two-dimensional wind tunnel, systematic experimental researches were carried out on the phenomenon of reverse transition on a heated plane with stable density stratification. The detailed experimental investigation of the distribution and evolution of the mean velocity profile were executed. The signal of instantaneous velocity, the energy spectra of velocity and wave characteristics in the boundary layer have been analyzed. All of these results described the process of the phenomenon and delineated the mechanism of it.The experiment was performed in two conditions:heated plane and unheated plane. When the plane was heated, observation showed that the shape factor increased from 1.5 to 2.6; the mean velocity profile departed from the law of the wall; the inertial sub-range in the energy spectra curves disappeared; the intermittent phenomenon occurred. All of the results indicated the turbulent boundary layer had been turned into the laminar layer. The skin friction coefficient drops rapidly. This result not only proved the phenomenon of reverse transition had occurred, but also showed that this condition was drag-reducing condition.