Flow Around a Normal Plate of Finite Width Immersed in a Turbulent Boundary Layer

Abstract

An experimental investigation was carried out on the flow around a normal plate of finite width mounted on a smooth plane wall along which a turbulent boundary layer was fully developed. Experimental data were collected to investigate the effects of (1) the aspect ratio of the plate (2) the parameters characterizing the boundary-layer on the pressure drag and the vortex shedding frequency. The pressure drag coefficient of the plate defined by CDτ = D/(1/2ρuτ 2 hw) was found to be expressed by a power function of huτ /ν in the range h/δ<1.0 for each aspect ratio w/h, where D is the pressure drag, uτ is the shear velocity, ρ is the density of fluid, h and w are the height and the width of the plate, respectively, ν is the kinematic viscosity, δ is the thickness of the boundary layer. Also, the Strouhal number for the plate defined by St =fc • w/ U0 was found to be expressed by a power function of the aspect ratio w/h in the range of h/δ less than about 1.0, where fc is the vortex shedding frequency, U0 is the free-stream velocity. As the aspect ratio was reduced, the type of vortex shedding behind the plate was found to change from the arch type to the Karman type at the aspect ratio of about 0.8.