Bodies subjected to fluid flow are classified as being streamlined or blunt/bluff, depending on their overall shape. A bluff body can be defined as a body that, as a result of its shape, has separated flow over a substantial part of its surface. Any body which when kept in fluid flow, the fluid does not touch the whole boundary of the object. An important feature of a bluff body flow is that there is a very strong interaction between the viscous and inviscid regions. When the flow separates from the surface and the wake is formed,the pressure recovery is not complete. Cylinders and spheres are considered bluff bodies because at large Reynolds numbers the drag is dominated by the pressure losses in the wake.
CRIACIV Wind Tunnel activities have been particularly aimed at the study of sharp-edged bluff-bodies, that is rectangular cylinders of several side ratio (defined as the ratio between the body depth facing the fluid flow on the body width parallel to it). It is worth noting that differnt side ratios imply completely different features in the flow field around the body. This, in turn, have consequencies on the aeroelastic behaviour, which has to be often investigated after having assessed the aerodynamical characteristics of the cross-section.
