影响板间蠕变拖曳流中涡流作用的因素

Analysis on Vortex in Drag Creeping Laminar-flow of Coating Fluids Between Plates

采用复值函数理论和有限元方法,对基底板和平板之间的牛顿流体和非牛顿流体的蠕变拖曳层流过程进行了数值研究,重点分析了雷诺数、剪切变稀系数和阻通比的变化对于两板间薄膜流动过程中涡流的产生和发展的影响.研究结果表明:雷诺数在一定条件下也会产生涡流,且会影响涡流的作用区域,但这种影响有限,因为流场中存在过大的速度梯度,所以雷诺数不是影响涡流的主要因素,对于不同的基底板形态,雷诺数对于涡流的作用相近;对于非牛顿流体,剪切变稀系数不会对流场的形态产生过多影响,但是,随着剪切变稀系数增大,发生流线分离的位置在纵向上会逐渐升高,涡流作用的区域增大,作用强度增强,使得流动更加不稳定;随着平均板距增大,临界波形度绝对值也随之增大,阻通比则随之减小,这表明临界阻通比随着波形度增大而呈现减小的趋势.

By using complex function theory and Finite Element Method, creeping drag laminar flows of Newtonian and Non-Newtonian Fluids between plates are numerically studied, and the influence from Reynolds Number, shear-thinning coefficient and blockage-passage ratio on the emergence and evolvement of vortex is analyzed. Researches indicate that with some qualifications, the increase of Reynolds Number also would bring out vortex and enlarge the areas vortex affects, but this influence is limited. The reason why Reynolds Number is not the key factor to vortex is the great velocity gradient inside the flow. With different profiles of substrate plate, the influence from Reynolds number on vortex is similar. While for the Non-Newtonian Fluids, shear-shinning coefficient puts little impact on the flow configuration, but its augment heightens the position where flow separation occurs and boost up the range and intensity of vortex, which makes the flow field further unsteady. As the average plate-distance increases, the absolute value of critical waviness also enhances, while the blockage- passage is on the contrary, which shows that critical blockage-passage trends to decrease with the augment of waviness.