Development of turbulent boundary layer in sudden change of upstanding surface roughness

Abstract

Turbulent flows over the flat surface undergoing a sudden change of surface roughness were studied experimently. The experiment was carried out in a wind tunnel test section, the floor of which was used as t'lesurface of interest. The surface was artificially roughned by thin synthetic fibres giving a brush like structure of average height 23.2 mm (0.913 inch). The flow parameters were 5 5 measured at three Reynolds number viz. B.74XIO , 5.06XIO and 5 2.56XIO . Measurement of boundary layer parameters was done by pitot static tube. The flow became fully developed over the .rough surface at 3.5 duct width of the tunnel from the rough-smooth junction. Sharp pressure drop in the rough-smoothe junction indicates high dissipation of energy in the transition zone. Friction factor over the rough surface is found to be dependent on Reynolds number. The growth of intern~l boundary layer is proportional to xO.49 Origin of the rough surface is observe j 0.6 inch below the crest of the roughness element, Equivalent sand roughness of the surface is found to be 3.23 m.m (0.127 inch)