Drag reduction of boat-tailed bluff bodies through transverse grooves

The present work describes a strategy for the aerodynamic drag reduction of elongated axisymmetric bluff bodies, which can be viewed as simplified models of road vehicles. One well-known method to reduce the drag of this type of body is a geometrical modification denoted as boat-tailing, which consists in a gradual reduction of the body cross-section before a sharp-edged base (Maull et al, J R Aeronaut Soc 71, 854–858, 1967, [1], Mair, Aeronaut Q 20, 307–320, 1969, [2], Wong and Mair, J Wind Eng Ind Aerodyn, 12, 229–235, 1983, [3]). We combine herein boat-tailing with properly contoured transverse grooves to further delay boundary-layer separation and to reduce drag

Flow Separation Delay and Drag Reduction Through Contoured Transverse Grooves

The results of several investigations aimed at assessing the performance of contoured transverse grooves as a method to delay flow separation are described. The physical mechanism at the basis of this passive technique is the local relaxation of the no-slip boundary condition, with a consequent reduction of the viscous losses and an increase of the downstream near-wall momentum. Numerical simulations and experiments showed that the application of one groove transverse to the flow direction may delay boundary layer separation both in laminar and turbulent conditions. As a consequence, significant increases of the pressure recovery in plane diffusers and decreases of the drag of boat-tailed axisymmetric and two-dimensional bluff bodies were obtained. It is shown that robust configurations may be devised provided the shape and dimension of the grooves are suitably chosen in order to assure the formation of steady and stable local flow recirculations