Flow field in confined impinging jets of Newtonian and non-Newtonian fluids

A three-dimensional numerical investigation is conducted to characterize laminar confined impinging jets of Newtonian and shear-thinning fluids issuing from a rectangular duct. The jet impinges normally on a flat plate and subsequently divides into two streams confined by inclined plane walls, forming a diverging channel representative of compact fluid-handling devices. Shear-thinning fluids are modeled as purely viscous power-law liquids, enabling systematic variation of rheological properties while isolating viscous effects. The governing equations are solved using a finite-volume method with second-order accurate discretization schemes on non-orthogonal collocated grids. Numerical predictions are validated against detailed experimental velocity measurements for both Newtonian and non-Newtonian fluids over Reynolds numbers between 10 and 800. The validated simulations are used to examine pressure losses, recirculation dynamics, and the three-dimensional flow structures that arise within the confined cell. The results show that total pressure losses are dominated by irreversible contributions associated with wall friction and flow separation, while reversible pressure recovery becomes significant only at the highest Reynolds numbers. Recirculation length increases with the Reynolds number for all fluids but exhibits a Reynolds-number-dependent and non-monotonic variation with shear-thinning intensity. Owing to the finite spanwise extent of the rectangular geometry, pronounced three-dimensional effects develop, including spanwise variations of recirculation length and secondary vortical motions characterized by helical trajectories within the separated regions. These secondary motions redistribute momentum across the span and significantly influence both separation dynamics and dissipation mechanisms. By resolving the full three-dimensional flow field, the present study clarifies the role of spanwise confinement in governing pressure-loss mechanisms and recirculation behavior in confined impinging jets, providing new insight into complex laminar flows involving geometric confinement and nonlinear rheology.