• grooves
• boat-tail
• drag
• vortex shedding

The present work is aimed at experimentally and numerically testing a passive method of flow control to delay flow separation in adverse pressure gradients. This method consist in the introduction of contoured transverse grooves in the lateral surface of a boat-tailed bluff body. The considered body is composed by a 3:1 elliptical forebody and a rectangular main part followed by a circular-arc
boat tail.
From the numerical part, Variational Multi-Scale Large-Eddy Simulations (VMS-LES) are carried out at Re = 9.6×10^4 using a in-house developed numerical code based on a mixed finite-volume/finite-element method. In previous workS it has been already tested the effectiveness of grooves in delaying flow separation, now the purpose is to analyse the performance of spanwise-discontinuos grooves and comparing it with single and double spanwise-continuos groove performance. The idea of groove interruption arises from the fact that spanwise-continuos groove leads to a drag reduction despite the increase in regularity and correlation of the wake, which is negative in several practical applications, so the new strategy of discontinuos grooves is introduced in order to have the positive effect of the groove in delaying flow separation but at the same time producing a disturb for the correlation. Mean pressure coefficient and wall shear stress are investigated, together with a detailed analysis of the instantaneous field in order to understand the behaviour of the groove in unsteady flow field, as the one presenting vortex shedding.
For the experimental part, wind tunnel test are carried out for the single groove. Measuring differential pressures and hot-wire velocity. The body with groove allowed to delay flow separation, a drag reduction of the order of 16% is obtained. The wake width is reduced and an increase in the vortex shedding correlation is found by introducing the groove.