Experimental Rheology of Aqueous Xanthan Gum Solutions at Various Concentrations and Numerical Analysis of Their Laminar Flow in a Backward‐Facing Step With an Eccentric Obstacle

ABSTRACT This study combines experimental and numerical approaches to investigate the rheological behavior of aqueous xanthan gum solutions and their laminar flow through a backward‐facing step (BFS) equipped with an eccentrically positioned Flow‐Guiding Obstacle (FGO). The experimental characterization was performed for xanthan gum concentrations of 0.1, 0.2, 0.3, and 0.4 wt% using a rotational rheometer in controlled shear‐rate mode. The solutions exhibited pronounced shear‐thinning behavior, while the measured non‐zero normal stress provided complementary evidence of elastic contributions to their rheological response. However, the normal stress measurements were interpreted qualitatively, particularly for the dilute solutions, because a complete viscoelastic characterization was beyond the scope of the present study. For the numerical investigation, the experimentally determined rheological properties of the 0.1 wt% xanthan gum solution were used as input parameters in a finite element model. The generalized Newtonian Power‐law model was employed to represent the shear‐dependent viscosity of the fluid, while elastic effects were not explicitly incorporated into the numerical model. The flow through the BFS was investigated for different positions of the proposed FGO, namely EPO1 (D2/7), EPO2 (D2/5), and EPO3 (D2/3), over the investigated Reynolds‐number range. The numerical model was quantitatively validated against available reference data for a conventional BFS, showing good agreement with the experimental measurements. The results show that the FGO substantially modifies the flow structure downstream of the expansion and reduces the extent of the recirculation region. Among the investigated obstacle configurations, EPO3 provides the greatest reduction in the recirculation region and the most favorable flow organization. Pressure‐drop analysis shows that the unobstructed BFS has the lowest pressure drop, while EPO3 exhibits the lowest pressure drop among the three obstacle configurations. Thus, among the investigated obstacle configurations, EPO3 provides the most favorable balance between recirculation suppression and the additional hydraulic resistance introduced by the obstacle. Overall, the study provides experimental and numerical insights into the flow of shear‐thinning xanthan gum solutions in complex geometries. The findings highlight the potential relevance of passive flow‐control strategies based on obstacle positioning for the transport and processing of non‐Newtonian fluids, including applications in food‐processing systems, while further experimental validation with representative fluids and process‐specific geometries is required to assess their practical performance.