Transport of inertial particles by compressible turbulent flows in a curved pipe

In this study, direct numerical simulations are performed to investigate inertial particle transport in supersonic turbulent flow in a straight-to-bent pipe. Three particle populations with viscous Stokes numbers ( St + ) of 0.9, 4 and 16 are considered. It is revealed that under the combined influence of wall confinement, flow compressibility and centrifugal forces, distinct turbulent structures emerge in different pipe regions, leading to inertia-dependent particle dynamics. In the straight section, particle streaks and near-wall accumulation are more significant for St + = 4 particles. When entering the curved section, Görtler vortices along the outer bend enhance the streak formation and the accumulation of St + = 16 particles. Further downstream, expansion waves suppress Görtler vortices while Dean vortices become dominant, transporting particles along the sidewalls towards the inner bend, thereby reducing outer-wall collisions and accumulation. Particles tend to escape the confinement of Dean vortices and accumulate on the sidewalls. A larger Stokes number results in an earlier detachment, accompanied by higher collision frequency, particle accumulation and slip velocity. In contrast, small inertia particles follow the vortical motions more closely, migrating into the inner low-speed region and resulting in a higher local particle concentration. These different behaviours stem primarily from differences in the centripetal force imparted by the flow in the streamwise and circumferential directions. The strongest centrifugal effect occurs in the areas on both lateral sides of the pipeline. These elucidations offer new physical insights for modelling and predicting particle-laden turbulent flows in curved geometries.