Numerical investigation of flow around the sagging pipeline above an equilibrium scoured bed

Flow characteristics around a suspended pipeline with different sagging heights e/G above an equilibrium scoured bed are simulated using the Navier-Stokes equations integrated with the k−ω Shear Stress Transport Delayed Detached Eddy Simulation model. The Divergence Free Synthetic Eddy Method was utilized for creating the inlet boundary layer. The major findings are summarized: (1) At e/G≤0.14, the wake experiences a significant periodic vortex shedding, characterized by the formation of streamwise ribs and spanwise vortex tubes. However, when e/G≥0.69, vortex shedding in the wake ceases, and a superposed hairpin vortex structure forms in the wake of the top shear layer. (2) When e/G≤0.28, variations in sagging height do not affect the lift spectral peak frequency. However, at e/G=0.42 and 0.55, the lift spectral peak frequency slightly increases, and peak values are inconsistent along the pipeline's spanwise direction. (3) As e/G increases, the negative time-averaged lift coefficient first increases, then decreases, reaching its peak near e/G=0.55. While the bed shear stress below the pipeline's front surface increases significantly. The pipeline's top shear layer leads to significant fluctuations in the downstream shear stress, despite the absence of periodic eddy shedding. Additionally, a detailed analysis of the pressure field, streamlines, and entropy characteristics is conducted.