Effect of secondary currents on the flow and turbulence in partially filled pipes

Large-eddy simulations of turbulent flow in partially filled pipes are conducted to investigate the effect secondary currents on friction factor, first- and second-order statistics large-scale motion. The method is validated first simulated profiles mean streamwise velocity, normal stresses kinetic energy (TKE) shown be good agreement with experimental data. stronger half- three-quarters full compared quarter or fully pipe flows, respectively. origin examined by both TKE budget steamwise vorticity equation, providing evidence that originate from corner between free surface walls, which where turbulence production larger than sum remaining terms budget. An extra source found at near centreline bisector, due two-component asymmetric there. occurrence dispersive (due currents) reduces contribution shear stress results a reduction total factor flows half comparison flow. Furthermore, presence significant inhibits very-large-scale motion (VLSM), turn strength scales near-wall streaks. Subsequently, coherent structures generated streak instability transient growth significantly suppressed. absence VLSM less supposedly responsible for drag relative an equivalent Reynolds number.