OPEN CHANNEL FLOW VELOCITY PROFILES FOR DIFFERENT REYNOLDS NUMBERS AND ROUGHNESS CONDITIONS

A series of laboratory tests were carried out to understand the extent of effect of roughness and Reynolds number on mean velocity in both outer and inner scaling. To this end, four different types of bed surface conditions (impermeable smooth bed, impermeable rough bed, permeable sand bed and impermeable distributed roughness) and two different Reynolds number (Reh = 47,500 and 31,000) were adopted in the study. Sand particles of median diameter of 2.46 mm were used to create the roughness. The results show that the mean velocities collapsed well for different Reynolds number and for all different bed surfaces. The maximum velocity for all flow conditions were observed below some distances from the free surface. The location of maximum velocity is seen to be dependent on both of roughness and Reynolds number. The smooth bed test data agrees well with the standard log law and collapses well in viscous sub layer and overlap region. The extent of collapses is found to be dependent on Reynolds number. Friction coefficient is noted to be dependent on both the Reynolds number and roughness