Asymmetric particle transport in turbulent flows within concentric annular ducts

We present the first direct numerical simulations of particle-laden turbulent flow in concentric annuli to investigate the effects of transverse curvature over a range of Stokes numbers. The results demonstrate that transverse curvature induces asymmetric radial transport, with particles preferentially drifting toward the outer wall. Unlike canonical planar flows where turbophoresis universally drives near-wall accumulation, the present study identifies a distinct physical regime at the convex inner wall where centrifugal effect competes with turbophoresis. As a consequence, significant particle depletion is observed near the inner wall under strong curvature, and the transient concentration field exhibits a non-monotonic evolution, with the overshoot generally being more evident at higher Stokes numbers. By deriving a transport equation and applying Sturm-Liouville modal analysis, we identify the competition between asymmetric transport modes with different decay rates as the physical mechanism driving this non-monotonic evolution, and establish a reduced-order model that captures the dynamics of the particle concentration near the walls.