An experimental study of the incompressible, three-dimensional, turbulent flow separation around the base of a bluff obstacle on a flat surface is described. The bluff obstacle is a streamlined, right circular cylinder mounted with its axis normal to the flat surface. The flow environment is characterized by a body Reynolds number of 183,000, based on the diameter of the circular cylinder. The study includes surface flow visualizations, surface pressure measurements, and mean flow measurements. The mean flow measurements consist of total pressure, static pressure, and velocity distributions in three planes around the base of the streamlined cylinder. The results show the presence of a large, dominant vortex in the junction between the cylinder and the flat surface. This vortex was found to consist of low total pressure fluid from the boundary layer flow upstream of the junction. In addition to the three-dimensional flow measurements, extensive measurements in the two-dimensional turbulent boundary layer on the flat surface are reported. These results show the existence of small, but statistically significant, spanwise variations in the nominally two-dimensional turbulent boundary layer. A systematic approach for estimating the wall shear stress from velocity profile data in a two-dimensional turbulent boundary layer based on the method of least squares is presented. / Ph. D.