Plane flow of thixotropic elasto-viscoplastic materials through a 1:4 sudden expansion

• The flow of an elasto-viscoplastic thixotropic material through a sudden expansion is examined.
• The least-squares Galerkin finite element method was used to integrate the governing equations.
• The constitutive model is a modified Oldroyd-B model with structuring-level-dependent parameters.
• Results are presented in the form of isobands of the structure parameter and elastic strain fields.

A numerical investigation of an elasto-viscoplastic thixotropic fluid flowing through a 1:4 plane expansion is performed, using a recently proposed constitutive equation. The conservation equations are solved using a four-field Galerkin least-squares formulation in terms of the extra stress, pressure, velocity, and structure parameter—a scalar quantity that represents the structuring level of the material microstructure. The focus is on determining the effect of thixotropy, elasticity and viscoplasticity on the topology of yielded and unyielded regions of the expansion, on the field of structuring level, and on the field of elastic strain. Relevant ranges of the relaxation time, yield stress, and thixotropy characteristic time are investigated. The numerical results reveal significant effects of these parameters. The trends observed are physically sound and in accordance with the related literature.