管道非连续流体层流、边界层表达式及减阻分析

Analysis on expression of laminar flow and boundary layer and drag reducing in PNF

为求得管道非连续流体(Pipe Noncontinuous Fluid,PNF)的层流卡门动量积分和边界层厚度表达式,参考平板层流卡门动量积分关系,结合工程实践,对PNF的层流边界层卡门动量积分关系式进行了分析。引入不同边界条件,重新分析了PNF层流边界层内流速分布表达式;采用近似解法求解PNF壁面切应力,避免了解四次方程求PNF壁面切应力精确解;针对PNF壁面切应力误差公式,进行分析后并结合工程算例数据优选近似解系数,获得PNF壁面切应力近似解,进而求得该工程中的PNF边界层厚度表达式。通过进一步分析PNF雷诺数对摩擦阻力因数的影响可知,在层流的情况下,随着PNF雷诺数的增加,摩擦阻力减小,从而达到减阻的效果。

In order to obtain Carmen momentum integral relationship formulas of laminar flow and the expression of thickness of boundary layer in PNF（pipe non-continuous fluid）, in combination with Carmen momentum integral relationship formulas of flat plate laminar flow and engineering practice, Carmen momentum integral relationship formulas of laminar flow and boundary layer in PNF was analyzed. First, various boundary conditions were introduced to reanalyze the flow distribution expression of laminar flow and boundary layer in PNF. The approximate solution was applied to deduce the wall shear stress（WSS） in PNF, so as to avoid solving a quartic equation for exact solution of WSS in PNF. After analyzing the error formulas of WSS in PNF, the data of a certain engineering project were applied to optimize the coefficient of approximate solution, so as to obtain the approximate solution of WSS in PNF and further achieve the expression of thickness of PNF boundary layer in the project. In addition, the influence of Reynolds number of PNF on friction resistance factor was analyzed. It was found that with the increase in Reynolds number of PNF, the flow drag of the laminar flow reduced, and the effects of drag reducing was achieved.