Bifurcation phenomenon of inertial viscoelastic flow through gradual expansions

In this paper, viscoelastic fluid flows in planar gradual expansions are studied numerically for the first time. Expansion ratio is considered to be 1:3, and exponential Phan Thien-Tanner (EPTT) model is used as the constitutive equation. The investigation is carried out based on a numerical approach using finite volume method (FVM) and Pressure Implicit with Splitting of Operator (PISO) algorithm. Three angles of 30, 45, and 60° are selected to clarify the effects of gradual expansion angles. Combined effects of dynamics and rheological parameters on bifurcation phenomenon are investigated in detail. An analysis is conducted to elucidate the influences of Reynolds and Weissenberg numbers on the dynamics, shapes, length, and intensity of vortices in stable and unstable situations. The results proved that an increment in expansion angles destabilizes the flow regime.