Drag reductions of a submarine pipeline with elliptical profiles in a high-density turbidity current

Submarine pipelines face significant geohazards from turbidity currents, which can exert substantial hydrodynamic loads and threaten structural integrity. This study employs three-dimensional large-eddy simulation coupled with a density transport equation to systematically investigate the interaction between turbidity currents and four submarine pipeline configurations: circular, ellipse-circular, circular-ellipse, and fully elliptical profiles, with elliptical segment lengths ( α ) ranging from 0.75 D to 2.25 D , where D denotes the circular pipe diameter. The circular pipe baseline case reveals four characteristic interaction stages: initial, impact, transient, and quasi-steady, marked by distinct vortex evolution and pressure transients. Ellipse-circular configurations effectively reduce the initial peak drag force via suppression of recirculation zones, although performance diminishes during full interaction due to flow reorganization. Circular-ellipse pipes exhibit sustained drag reduction across most stages, with α = 1.75 D and 2.25 D performing optimally by limiting jet formation and shifting separation points. Fully elliptical pipes attenuate early-stage drag through streamlined profiles but exhibit elevated loads in later stages due to enhanced streamwise pressure gradients. Overall, the circular-ellipse configuration demonstrates superior drag-reduction performances, while all non-circular geometries show improved initial peak mitigation with increasing α . The maximum drag reductions in the first peak and global maximum value are observed to be 61.96% and 46.74% for the elliptical pipe at α = 1.75 D and 2.25 D , respectively. These findings provide critical insights for the optimal design of submarine pipelines under turbidity currents. • Interactions between turbidity currents and submarine pipelines are analyzed. • Four fluid-pipe interaction stages are identified. • Elliptical profiles are effective to reduce drag forces. • The circular-ellipse pipe presents superior drag-reduction performances.