Sediment-laden velocity profiles developed in a long boundary-layer wind tunnel

Abstract

A sediment-laden fully developed turbulent shear flow, over a plane aerodynamically-smooth, erodible sand surface, was established in a long (30 m) boundary-layer wind tunnel to investigate the influence of a nonuniform sand concentration distribution on velocity profiles. The main flow Reynolds number U mδ/ν covered a range from 3.2×10 5 to 1.2×10 6 as the concentration per mass varied between 0.0 and 0.7 which corresponds to a total transport rate per unit width of the tunnel of 0.042 kg/s-m. Velocity profile messurements were made using hot-wire anemometry throughout the entire boundary layer, with emphasis on the wall region. The analysis of mean velocity profiles demonstrates the applicability of the law-of-the-wall in the lower 10% of the boundary layer regardless of the sediment concentration. The upper 90% of the velocity profiles is best described by the law-of-the-wake. The profile parameter π increases with shear velocity from 0.6 for one-phase flow to an asymptotic value of 1.8, reached for main flow Reynolds number larger than 10 6 and sand concentrations per mass larger than 0.6 near the bed. The velocity measurements display wake distributions which are in excellent agreement with the function proposed by Coles (ref. 7) for one-phase fluids.