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Turbulent drag reduction over curved walls

Published online by Cambridge University Press:  28 May 2020

Jacopo Banchetti ,
Paolo Luchini Open the ORCID record for Paolo Luchini [Opens in a new window]  and
Maurizio Quadrio Open the ORCID record for Maurizio Quadrio [Opens in a new window]
Jacopo Banchetti
Affiliation:
Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, via La Masa 34, 20156Milano, Italy
Paolo Luchini
Affiliation:
Dipartimento di Ingegneria Industriale, Università di Salerno, 84084Fisciano, Italy
Maurizio Quadrio*
Affiliation:
Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, via La Masa 34, 20156Milano, Italy
*
†Email address for correspondence: [email protected]
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Abstract

This work studies the effects of skin-friction drag reduction in a turbulent flow over a curved wall, with a view to understanding the relationship between the reduction of friction and changes to the total aerodynamic drag. Direct numerical simulations are carried out for an incompressible turbulent flow in a channel where one wall has a small bump; two bump geometries are considered, that produce mildly separated and attached flows. Friction drag reduction is achieved by applying streamwise-travelling waves of spanwise velocity (StTW). The local friction reduction produced by the StTW is found to vary along the curved wall, leading to a global friction reduction that, for the cases studied, is up to 10 % larger than that obtained in the plane wall case. Moreover, the modified skin friction induces non-negligible changes of pressure drag, which is favourably affected by StTW and globally reduces by up to 10 %. The net power saving, accounting for the power required to create the StTW, is positive and, for the cases studied, is one half larger than the net saving of the planar case. The study suggests that reducing friction at the surface of a body of complex shape induces further effects, a simplistic evaluation of which might lead to underestimating the total drag reduction.

JFM classification

Flow Control: Drag reduction Turbulent Flows: Turbulence control Boundary Layers: Boundary layer control
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 896 , 10 August 2020 , A10
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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