Attitude-controlled drag model of elongated cylindrical bodies in confined annular flows

The coupling between body attitude and confinement-induced flow asymmetry influences the hydrodynamics of elongated cylindrical bodies in confined annular flows. However, conventional models relying on concentric and vertical assumptions fail to capture the enhanced energy dissipation induced by dynamic tilting and offset, severely limiting their predictive accuracy in realistic transport systems. In this study, we investigate the attitude-dependent hydrodynamic behavior using a resolved computational fluid dynamics–discrete element method (CFD–DEM) framework based on an immersed boundary method, systematically validated against instrumented “smart core” experiments. The results reveal that confinement forces the suspended core toward statistically stable suspension states characterized by preferential tilt-offset phase locking. A critical geometric wall-contact constraint is derived, physically bounding the admissible kinematic states by linking the inclination angle to the center-of-mass offset. Building on this constraint, an attitude-controlled drag model is formulated within an energy dissipation framework, which explicitly resolves the asymmetric annular contraction due to offset and the additional expansion loss induced by inclination. Comparisons with resolved simulations demonstrate that the proposed model significantly outperforms the concentric-assumption drag model, reducing the average drag prediction error by approximately 70%. This work presents a mechanism-based drag description for elongated cylindrical bodies in confined annular transport, providing new insights into confined hydraulic transport.