On the Interplay of Micropolarity and Viscoelastic Relaxation in Controlling Drag Within a Cavity Flow

The interplay between microrotation, microinertia, and viscoelastic relaxation significantly influences the hydrodynamic performance of non-Newtonian cavity flows. This study investigates the combined effects of the Eringen number, micropolar coupling constant, and fluid relaxation factor on drag force, microrotation, and flow behavior in a two-dimensional lid-driven cavity. The governing nonlinear partial differential equations are formulated using Eringen’s micropolar theory with relaxation-time-dependent stress, and the characteristic Galerkin finite element method is employed for numerical solution using a custom FreeFEM++ implementation. The results reveal a strong coupling between microrotation and viscoelastic relaxation effects. Increasing the relaxation factor enhances flow elasticity, leading to variations in drag force depending on the flow regime. The Eringen number stabilizes the flow and suppresses drag oscillations, while the micropolar coupling constant modulates shear-layer thickness and vortex intensity. Higher Eringen number increases kinetic energy and produces more ordered streamline patterns, whereas larger values of micropolar constant reduces drag while amplifying microrotation. Overall, tuning Eringen number, micropolar constant and time relaxation provides an effective mechanism for controlling drag and optimizing flow stability. These findings offer valuable insights for the design of advanced microfluidic and rheological systems where microstructural and viscoelastic effects coexist.