基于格子Boltzmann两相模型的粘弹流体挤出胀大分析

Analysis of Viscoelastic Fluid Extrusion Swell Based on Lattice Boltzmann Two-Phase Model

挤出胀大的数值模拟是非牛顿流体研究中具有挑战性的问题.本文运用格子Boltzmann方法(LBM)分析Oldroyd-B和多阶松弛谱PTT粘弹流体的挤出胀大现象,采用颜色模型模拟出口处粘弹流体和空气的两相流动,通过重新标色获得两种流体的界面,并最终获得胀大的形状.Navier-Stokes方程和本构方程的求解采用双分布函数模型.将胀大的结果与解析解、实验解和单相自由面LBM结果进行了比较,发现格子Boltzmann两相模型结果与解析解和实验结果相吻合,相比于单相模型,收敛速度更快,解的稳定性更高.研究了流道尺寸对胀大率的影响,并对挤出胀大的内在机理进行了分析.

The numerical simulation of extrusion swell is a challenging task in non-Newtonian research.In this paper the lattice Boltzmann method is applied to the extrusion swell simulation of viscoelastic fluid described by the Oldroyd-B and multi-mode PTT constitutive equations.Two-phase flow outside channel is simulated using the color model and the free surface of flow obtained by recoloring.The Navier-Stokes equations and the constitutive equations are solved using double distribution functions.A set of numerical tests is conducted to show that the numerical results are in agreement with some available analytical solutions and experimental data.The convergence speed of the two-phase model is faster than that of the single-phase model.The effect of channel size on the swelling rate is studied,and the intrinsic mechanism of extrusion swelling is analyzed.