Flow separation delay and drag reduction through contoured transverse grooves

Flow control is of great importance in many engineering applications to attain desired characteristics. Several investigations have been carried out aimed at assessing the performance of contoured transverse grooves as a passive method to delay boundary layer separation. Tests are carried out in the subsonic wind tunnel of DICI, while simulations are carried out using research and in-house-developed codes.
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. A synergic use of high-fidelity 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 increase of the pressure recovery in plane diffusers and decrease 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.

Research group

Maria Vittoria Salvetti
Alessandro Mariotti
Elena Pasqualetto

External collaborations:
ISCRA CINECA Grant: Bluff-Body Base Drag REDuction through boundary-layer modification – B3DRED (HP10BL3T2N)

Main publications:

• Mariotti A, Grozescu AN, Buresti G, Salvetti MV (2013) Separation control and efficiency improvement in a 2D diffuser by means of contoured cavities. Eur J Mech B Fluid 41:138–149
• Mariotti A, Buresti G, Salvetti MV (2014) Control of the turbulent flow in a plane diffuser through optimized contoured cavities. Eur J Mech B Fluid 48:254–265
• Mariotti A, Buresti G, Salvetti MV (2015) Use of multiple local recirculations to increase the efficiency in diffusers. Eur J Mech B Fluid 50:27–37
• Mariotti A, Buresti G, Gaggini G, Salvetti MV (2017) Separation control and drag reduction for boat-tailed axisymmetric bodies through contoured transverse grooves. J Fluid Mech 832:514–549
• Mariotti A, Buresti G, Salvetti MV (2019) Separation delay through contoured transverse grooves on a 2D boat-tailed bluff body: effects on drag reduction and wake flow features. Eur J Mech B Fluid 74:351–362