Effect of Surfactant Additives on Generation and Development of Laminar Boundary Layer on a Flat Plate

Abstract

The effect of surfactant solutions on laminar boundary layer over a flat plate has been investigated at Re < 15.3×103 by measuring the velocity profile using a PIV system. It was clarified that the boundary layer thickness of surfactant solutions increases significantly compared to that of tap water. In the upstream region of the leading edge, the boundary layer (or the stagnation area) has already been generated and the thickness of this area is already large. In the downstream region, the velocity profiles of all surfactant concentrations at the near-wall region, are similar, but not identical, to that of tap water. At the far-wall region of the boundary layer, the velocity profile is significantly different. For higher surfactant concentrations, the velocity profile describes like S-shape profile, which is greatly different from that of lower concentration. When the Reynolds number increases, the velocity profile of the surfactant solution gradually develops. The dependence of the boundary layer thickness of the surfactant solution on the distance downstream from the leading edge is similar to that of tap water. Consequently, the surfactant gives large effect for not only development of the boundary layer but also the generation of it.