切应力作用下的液膜稳定性分析

Stability Analysis of Liquid Films Under Shear

气液界面存在同向或反向切应力时,在一定程度上影响到液膜的水动力学特性和流动稳定性,并改变其热质传递特性。基于完整的边界条件,建立了切应力作用下沿倾斜壁面下降的液膜表面波的Orr-Sommerfeld方程。采用摄动方法求解出波速表达式,分析了切应力、雷诺数、波数、表面张力、倾角和温度等参数对液膜稳定性影响。研究表明:同向切应力为不稳定性因素,反向切应力的稳定性影响与第一和第二临界切应力有关;反向切应力使临界雷诺数增大,同向切应力使其减小;波数和流体温度对稳定性的影响与切应力的方向也密切相关。

The shear stress at plays an important role on the liquid-gas interface characteristics of the hydrodynamics, flow stability and heat transfer of liquid film. The Orr-Sommerfeld equation describing the flow stability of liquid films under shear draining down an inclined wall was established based on complete boundary conditions. The wave velocity was computed with the perturbation method. The present model included the effects of shear stress, Reynolds number, wave number, surface tension, inclination angle and liquid temperature. Computed results show that the cocurrent shear has an adverse impact on stability and the effects of countercurrent shear on stability is related to the first and second critical shear stresses. The critical Reynolds number decreases under the countercurrent shear and increases under the cocurrent shear. Results also show that the effect of wave number and liquid temperature on stability is closely related with the shear direction.