Turbulent separations beneath semi-submerged bluff bodies with smooth and rough undersurfaces

The spatio-temporal characteristics of turbulent separations beneath semi-submerged bluff bodies with different undersurface roughness conditions are studied using a time-resolved particle image velocimetry. Reynolds number based on the free-stream velocity and submergence depth was fixed to 14 400. Three – smooth, sandpaper cube were examined. results showed that wall reduces mean reattachment length, suppresses stresses in second half separation bubble. Kelvin–Helmholtz instability is observed at leading edge smooth body, but bypassed rough cases. In first bubble, frequencies separated shear layer migrate lower values discrete manner through vortex pairing mechanism. Consequently, multiple shedding motions nested layer, cores shed vortices aligned near isopleth velocity. accompanied along flow reversal upstream locations. These influenced significantly by roughness. A low-frequency flapping motion manifests as enlargement/shrinkage reverse areas cases similar, relatively than case. This associated an extremely large from point region.