Influence of incident vortex street on separated flow around a finite blunt plate: PIV measurement and POD analysis

Abstract

This study investigated the influence of incident vortex street on the spatial characteristics of separated shear layers around finite blunt plates through use of planar particle image velocimetry. Three systems with different chord-to-thickness ratios (c/t) were chosen for the comparative study (i.e., c/t=3.0, 6.0 and 9.0). The Reynolds number, based on the plates׳ thickness (t), was Ret=1000. The incident vortex street was generated by placing a circular cylinder (D=t) far upstream of the plate. For the systems without incident vortex street, the separated shear layers around the shortest (c/t=3.0), the median-length plate (c/t=6.0) and the longest (c/t=9.0) plates had no re-attachment, periodic re-attachment and faithful re-attachment on the plate׳s surface, respectively. However, the separated shear layers subjected to incident vortex street were restrained at the leading edges by the upstream vortical structures, which were less influenced by increases in chord-to-thickness ratio. Contour plots of the spatial v–v correlation coefficient revealed that the wakes behind plates longer than c/t=6.0 were not severely influenced by incident vortex street. Distributions of the spatial v–v correlations and the POD eigenmodes revealed that the incident vortical structures were split by the leading edges of the plates in all systems, resulting in two vortices with the same rotating direction. Subsequently, a further phase-averaged analysis convincingly demonstrated the splitting process of the incident vortical structures by the leading edges.