Vortex shedding mechanism from prisms having H and I sections

Abstract

In case of the flow around the H-section prism, a single and double shear layer instabilities coexist. It is found that the fundamental frequency due to the single shear layer instability along the shear layer between the upper (or lower) leading edge and upper (or lower) trailing edge is adjusted so as to coincide with that due to the double shear layer instability behind the prism, and vice versa. On the other hand, in case of the flow around the I-section prism, there exists only a double shear layer instability, and asymmetry of the vortex pair in the vortex formation region and the subsequent transformation into the unstable system of the three vortices, viz., upper main vortex, lower main vortex and third vortex, leads to the alternate vortex shedding. It is realized that the vortex shedding mechanism from the I-section prism is essentially same as that from a circular, triangular or square prism.