SEDIMENT-LADEN VELOCITY PROFILES DEVELOPED IN A LARGE BOUNDARY-LAYER WIND TUNNEL (TURBULENCE, SAND TRAPS, VON KARMAN, SHEAR-STRESS)

A sediment-laden fully developed turbulent shear flow, over an aerodynamically smooth erodible sand surface, was established in a large boundary-layer wind tunnel to investigate the influence of a nonuniform sand concentration distribution on velocity profiles and turbulence characteristics.; The Reynolds number of the flow, calculated from the free stream velocity and the boundary-layer thickness, covered a range from 3.2 x 10('5) to 1.2 x 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 measurements were made throughout the entire boundary layer, with emphasis on the inner layer. The mean and turbulent components were measured with a single hot wire. Sand concentration profiles were measured with a newly designed isokinetic sand sampler.; 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. A method, based on similarity between turbulence relative intensity profiles, has been developed to evaluate the von Karman (kappa), and demonstrates its independence from sand concentration. The upper 90 percent of the velocity profiles is best described by the law-of-the-wake. The profile parameter (PI), increases with shear velocity from 0.6 for clear flow to an asymptotic value of 1.8 reached for main flow Reynolds number larger than 10('6) and sand concentrations larger than 0.6 near the bed. The velocity measurements display wake functions which are in excellent agreement with the function proposed by Coles (1956). It has also been shown that the root-mean-square velocity varies inversely with the local sand concentration. Finally, an empirical equation was derived to demonstrate a dependence of the sand transport rate on the square root of the elevation over the sand bed.; Among the most important conclusions are that sediment concentration does not affect the following: (1) The law-of-the-wall, in its domain of validity, (2) The value of the von Karman (kappa), (3) The wake flow function suggested in the literature for homogeneous fluids.