Non-Newtonian fluid–structure interaction in three-dimensional collapsible tubes: An immersed boundary-lattice Boltzmann method

The effects of non-Newtonian rheology on the dynamics of three-dimensional collapsible tube systems are investigated numerically using an immersed boundary-lattice Boltzmann method coupled with a finite element structural solver. A power-law constitutive model is employed to characterize shear-dependent viscosity effects across a wide range of power-law indices (n=0.7–2.0). The results reveal that fluid rheology significantly modifies the system's dynamic response and apparent stability: shear-thickening fluids (n>1) stabilize the collapsible tube and suppress flow-induced oscillations, while shear-thinning fluids (n<1) promote instability and trigger self-excited oscillations. Mechanistically, shear-thinning effects amplify local velocity gradients in collapsed regions, enhancing fluid–structure coupling and destabilizing the system. In contrast, shear-thickening effects increase effective viscosity in the high-shear areas, providing mechanical damping that suppresses oscillations. The rheological properties significantly affect both structural deformation patterns and the pressure drop—flow rate relationship, with these effects demonstrating the critical importance of accounting for non-Newtonian behavior in physiologically and technologically relevant applications.