气体辅助聚合物挤出中的二维等温粘弹流动的数值模拟

以圆棒挤出为例，采用通用的流体力学有限元软件FIDAP，以壁面剪切应力为零的边界条件代替气体辅助挤出过程中的气垫膜层的作用对新型挤出方式——气体辅助挤出二维等温流动进行了粘弹数值模拟，得出和分析了口模内外的流线、速度、压力、应力分布和挤出胀大率等模拟结果，并将模拟结果和传统挤出进行了对比．分析和对比表明：气辅挤出可以基本消除挤出胀大，和传统挤出时的速度场、压力场和应力场在口模出口处沿轴向和径向均变化剧烈，而口模内部变化平缓的情况相比，气辅挤出时在有气辅段内各处的流线、速度、压力、应力很快趋同，到出口处几乎完全一致，从而可有效消除挤出过程中的“鲨鱼皮”现象，提高挤出制品的表面质量。

Numerical Simulation of Two Dimensional Isothermal Viscoelastic Polymer Flow in Gas-assisted Extrusion

Taking the boundary condition of non shear stress as the effect of the gas layer between the die wall and the polymer interface,the numerical simulation of two dimensional isothermal viscoelastic polymer flow in gas assisted round-stick extrusion,was performed by means of FIDAP software.The die swell ratio and streamline,velocity,pressure and stress distributions inside and outside the die were worked out,analyzed and compared with those simulation results worked out for the conventional extrusion.Analysis and comparison show that for the gas assisted extrusion,the die swell ratio can be greatly reduced and the changes of velocity,pressure and stress are drastic near the inlet of gas and disappear at the outlet of the die,which can prevent occurrence of 'shark skin' effectively and thus improve the quality of the extruded products,while for the conventional extrusion,all of the velocity,pressure,and stress change mildly inside the die but drastically near the outlet of die.