Computation of boundary shear stress distribution along the wetted perimeter of a rectangular open channel

ABSTRACT

This study evaluates the distribution of boundary shear stress along the wetted perimeter of a smooth rectangular open channel under supercritical flow using three-dimensional computational fluid dynamics (CFD). A finite-volume model was built in ANSYS Fluent, a commercial computational fluid dynamics (CFD) software package solving the Reynolds-averaged Navier–Stokes (RANS) equations with the standard k–ε turbulence closure and tracking the free surface with the volume-of-fluid (VOF) method. The numerical model was first validated against the Preston-tube experimental measurements, obtained in a 9.75 m smooth rectangular flume; the maximum discrepancies between the measured and predicted shear stress were 8.20% at the bed and 11.72% at the side wall. The validated model was then extended to twelve additional numerical runs covering two channel widths, bed slopes between 5 × 10−3 and 2 × 10−2, and Froude numbers of 1.2–4.1. The results confirm that the bed shear stress is consistently greater than the side-wall shear stress, peaks at the channel centerline, and decreases toward the side walls; increases with bed slope; and decreases as the Froude number increases; the side-wall shear stress rises with depth to a maximum before decaying to zero near the free surface. These outcomes provide quantitative information relevant to the assessment of bed and side-wall erosion in smooth rectangular channels under the investigated supercritical-flow conditions.