Startup flows of wormlike micelles solutions in a three-dimensional rectangular abrupt contraction channel are numerically simulated using a modified Bautista-Manero model as a constitutive equation. The numerical scheme applied is based on the finite volume method with the PISO algorithm, and the DEVSS method is employed to stabilize the numerical computation. Temporal changes in micelle network structures are investigated based on the analysis of the fluidity, which represents the structural change in micelle networks. The numerical results indicate that the orientation behavior of micelle networks around the entrance to the contraction remarkably changes with time. Around the entrance, micelle networks undergo strong elongation and shear deformations and hence the deformation of network is accelerated. Furthermore, the velocity distribution in a cross section takes a plug-like profile similarly to that of viscoplastic fluids because the fluidity rapidly changes near channel walls, where the shear rate is high. Three-dimensional patterns in the distribution of the fluidity appear more remarkably at high Weissenberg numbers, while in a conduit downstream of a contraction part they appears in a limited region near the walls where the fluidity rapidly changes.

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