Separation delay and drag reduction through contoured transverse grooves in a boat-tailed bluff body with vortex shedding

The reduction of the aerodynamic drag of blunt-based bluff bodies with a wake characterized by alternate shedding of vortical structures is interesting for several applications. One well-known method to reduce the drag of this type of body is a geometrical modification called boat-tailing, consisting in a gradual reduction of the body cross-section before a sharp-edged base. We combine boat-tailing with properly contoured transverse grooves to further delay boundary-layer separation and reduce drag.

The considered geometry cross-section has an elliptical forebody and a rectangular main body followed by a circular-arc boat tail. The effectiveness of the contoured grooves is herein assessed through experiments in addition to simulations. The introduction of a single transverse groove leads to a significant increase of the pressure on the body base and, consequently, to a reduction of drag compared with the boat-tailed body without the groove. This is due to a delay of flow separation over the boat tail. A steady local recirculation is present inside the groove and downstream its reattachment the boundary layer is thinner and has higher momentum than in the case with no groove, allowing separation to be delayed.