聚合物熔体挤出胀大的三维数值模拟

采用粘弹性PTT模型对聚合物熔体的矩形口模挤出胀大进行了三维等温数值模拟,得出了不同条件下的口模外流动速度和挤出胀大率沿挤出方向的分布规律.模拟时利用罚函数有限元法和把动量方程转化成椭圆类方程的去耦算法以降低模拟对计算机内存的要求和增加计算收敛的稳定性,采用用路线法对挤出胀大自由表面进行更新迭代.模拟结果表明:We数越大,则挤出胀大率越大,而且对于矩形口模挤出而言,高度方向的挤出胀大率比宽度方向的挤出胀大率大.

Three-dimensional Numerical Simulation of Extrudate Swell of Polymer Melts

In this paper, on the basis of the Pham Thien-Taner constitutive model, the three dimensional isothermal numerical simulation was conducted for the swell of polymer melts extruded from a rectangular die.The distribution of the flow velocity outside the die and the extrudate swell ratios along the extrusion direction were obtained. In order to reducing computer memory capability required for computation and enhancing the convergence stability of iterative process, the penalty finite element method was adopted and the momentum equation was transformed into an elliptic equation. The pathline method was used for the iterative renewal of the free surface of extrudate. The results of numerical simulation show that the swell ration increases along with increase of the Weissenberg Number(we) and for the swell of extrudate from a rectangular die, the swell ratio in highness is larger than that in width.