Aerodynamic characteristics acting on rectangular prisms remarkably vary with the side ratio of the prisms. The variation of wind forces with the side ratio is caused by the aerodynamic interaction between the separated shear layer and the after-body of the prism. Especially, the re-attachment of the separated shear layer on the after-body of the prism yields the remarkable variation of wind forces. When wind attacks obliquely to a prism, the re-attachment of the flow obviously occurs on one side surface of the prism. In this condition, fluctuations of wind forces decrease and Strouhal numbers increase. The phenomenon is similar to the variation of wind forces by the side ratio of prisms of which the front face is normal to a wind.
