{"id":462811,"date":"2026-08-21T07:11:34","date_gmt":"2026-08-21T07:11:34","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/polyflow-viscoelastic-model-does-not-converge-to-newtonian-case\/"},"modified":"2026-08-21T07:11:34","modified_gmt":"2026-08-21T07:11:34","slug":"polyflow-viscoelastic-model-does-not-converge-to-newtonian-case","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/polyflow-viscoelastic-model-does-not-converge-to-newtonian-case\/","title":{"rendered":"Polyflow Viscoelastic model does not converge to Newtonian case"},"content":{"rendered":"
\n

Hello everyone,<\/p>\n

I am trying to perform a simulation in Polyflow using a viscoelastic material model, but I am obtaining results that are completely different from my Newtonian reference case.<\/p>\n

Reference Newtonian case<\/h3>\n

I first set up an isothermal Newtonian filament stretching simulation (viscosity = 80 pa.s) and a strong stretching force<\/strong>, which runs correctly. The fiber attenuates as expected and after about 0.1 s<\/strong> a long fiber is already formed.<\/p>\n

Viscoelastic case<\/h3>\n

I then duplicated the exact same setup and only changed the material model to a Differential Viscoelastic Isothermal Flow<\/strong> model (I tested both Maxwell<\/strong> and Oldroyd-B<\/strong>). <\/p>\n

For simplicity:<\/p>\n

    \n
  • Constant viscosityof 80 pa.s<\/li>\n
  • Same geometry, mesh, boundary conditions and operating conditions as the Newtonian case<\/li>\n
  • Activated “Couple computation of viscoelastic stresses”<\/strong><\/li>\n
  • Very small relaxation time<\/li>\n<\/ul>\n

    In particular, I set the relaxation time to λ = 10\u207b¹\u2070 s<\/strong>, expecting the solution to become essentially Newtonian.<\/p>\n

    Problem<\/h3>\n

    Instead of approaching the Newtonian solution:<\/p>\n

      \n
    • The fiber barely stretches, the material remains as a thick bulge.<\/li>\n
    • Even after extending the simulation time, I only obtain something similar to a large droplet\/bead, with almost no attenuation.<\/li>\n<\/ul>\n

      This behavior remains even when the relaxation time is reduced to 10\u207b¹\u2070 s<\/strong>, which is surprising because I would expect the viscoelastic model to recover the Newtonian solution in that limit.<\/p>\n

       <\/h3>\n

      Has anyone experienced a similar issue with free-surface fiber spinning simulations in Polyflow?<\/p>\n

      Is there a specific setting, stabilization method, scaling issue, or material parameter that must be adjusted when using differential viscoelastic models?<\/p>\n

      More specifically, is there any reason why a viscoelastic simulation with a relaxation time of 10\u207b¹\u2070 s<\/strong> would still produce results that are drastically different from the corresponding Newtonian case?<\/p>\n

      Any suggestions would be greatly appreciated.<\/p>\n

      Thanks!
      Romain<\/strong><\/p>\n<\/div>\n","protected":false},"template":"","class_list":["post-462811","topic","type-topic","status-publish","hentry","topic-tag-polyflow","topic-tag-polymer","topic-tag-polymer-extrusion-3"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t