On the Connection between the Transverse Force and Flow Separation on Galloping Prone Rectangular Cylinders

Symmetric bluff bodies that are prone to flow induced vibration due to transverse galloping are characterized by the formation of open separation along their sides at zero angle of attack (AoA). As the AoA increases, the magnitude of the mean transverse force coefficient increases from zero until it reaches a maximum at the critical AoA α_c. In the galloping literature (e.g. Naudascher & Rockwell, 2005), there is a consensus that α_c corresponds to the AoA where the shear layer reattaches on the windward side of the body. In this talk, we use high-resolution single-component molecular tagging velocimetry to capture the boundary layer behavior around high-aspect-ratio rectangular cylinders with side ratio of 2 in the Reynolds number range (based on model thickness) 1,000<Re_d<10,000. The results show that significant deviation could exist between and the AoA at which the shear layer reattaches on the body. The deviation seems to be connected to the geometry (corner roundness) and/or the Reynolds number.