Investigation of flow structure from a vertical and horizontal cylinder in shallow water

In this study, vortex structure in the wake region of the vertical and horizontal cylinders was investigated in shallow water layer using a technique of high-image- density Digital Particle Image Velocimetry (PIV). The formation of a large-scale Karman vortex from a vertical cylinder involves upward ejection of fluid through its center which eventually turns into a horizontal vortex that induces significant distortion of the free-surface. Vortex formation from a vertical cylinder in shallow water layer is controlled by placement of narrow transverse strip of roughness elements on the bed (bottom surface). It is demonstrated that even the smallest roughness height clearly attenuates the onset of large-scale, Kârmân-like vortex formation in the region close to the base of the cylinder, relative to the case of no roughness. In the second arrangement, the cylinder was submerged horizontally beneath the free-surface of the shallow water. The upper surface of the cylinder was adjusted in order to be coincident with the free-surface. The diameter of the horizontal cylinder was gradually increased in order to determine the values that exhibited major changes in the near- wake patterns. The streamline topology in the very near- wake of each cylinder is a strong function of the cylinder diameter and the Froude number. Key Words: Wake region, Vortex formation, Shallow water flow, DPIV, Circular cylinder