Particle Image Velocimetry (PIV) Investigation of Local Scour Around Emergent and Submerged Circular Cylinders

Analysis of the velocity field surrounding a circular cylinder under equilibrium of local scour has been restricted due to practical limitations of commonly used measurement techniques. This investigation summarizes select cases in the literature which have attempted to circumvent such limitations and presents flow field measurements using Particle Image Velocimetry (PIV). Scour tests were conducted in a horizontal flume fitted with a sediment recess containing erodible bed material. Tests were conducted with both emergent and submerged circular cylinders for a period of 24 hours, after which equilibrium was achieved and planar PIV measurements were obtained in the streamwise-vertical symmetry plane. Analysis of bed profiles and the distribution of the mean velocity indicated that the scour depth upstream of the cylinder was slightly (2 percent) higher for the emergent case, and separation of flow over the top of the submerged cylinder affected the formation of the dune in the wake of the cylinder