The structure of the turbulent boundary layer on a cylinder in axial flow

Abstract

The thick, turbulent boundary layer, which develops as a fluid flows parallel to a cylinder, has been experimentally characterized for the case where the boundary layer is thick compared to the radius of transverse curvature. Measurements of the turbulence intensity, velocity spectra, and intermittency are qualitatively similar to those for the planar boundary layer. Although measurements of wall shear stress using several different techniques have substantial scatter, the wall shear stress appears to be larger than that for the turbulent boundary layer on a flat plate at the same Reynolds number based on streamwise distance. The variable interval time averaging (VITA) and uv-quadrant techniques were used to detect the burst cycle near the wall. Conditionally averaged velocities were similar to those for a flat plate boundary layer indicating a similar burst cycle near the wall. However, the VITA frequency scaling indicates an interaction between the flow in the wall region and the outer flow. Flow visualization was used to observe the crossflow of structures in the boundary layer of a cylinder moving through a tank of quiescent water. Large-scale structures were observed moving from the outer region on one side of the cylinder to the outer region on the opposite side of the cylinder suggesting that the wall may be less important in controlling the size and motion of coherent structures in the cylindrical boundary layer than in the planar boundary layer.