Drag reduction by herringbone riblet texture in direct numerical simulations of turbulent channel flow

ABSTRACT

A bird-feather-inspired herringbone riblet texture was investigated for turbulent drag reduction. The texture consists of blade riblets in a converging/diverging or herringbone pattern with spanwise wavelength Λ_f. The aim is to quantify the drag change for this texture as compared to a smooth wall and to study the underlying mechanisms. To that purpose, direct numerical simulations of turbulent flow in a channel with height L_z were performed. The Fukagata-Iwamoto-Kasagi identity for drag decomposition was extended to textured walls and was used to study the drag change mechanisms. For Λ_f/L_z ≳ O(10), the herringbone texture behaves similarly to a conventional parallel-riblet texture in yaw: the suppression of turbulent advective transport results in a slight drag reduction of 2%. For Λ_f/L_z ≲ O(1), the drag increases strongly with a maximum of 73%. This is attributed to enhanced mean and turbulent advection, which results from the strong secondary flow that forms over regions of riblet convergence/divergence. Hence, the employment of convergent/divergent riblets in the texture seems to be detrimental to turbulent drag reduction.

KEYWORDS:

• Drag reduction
• riblets
• direct numerical simulations

Acknowledgments

The research leading to these results has received funding from the European Union Seventh Framework Programme in the SEAFRONT project under grant agreement nr. 614034. The simulations were performed on the Dutch national supercomputer Cartesius at SURFsara, Amsterdam, The Netherlands. This work was sponsored by NWO Physical Sciences for the use of supercomputer facilities. H.O.G.B. would like to thank his colleague Pedro Costa for his supercomputational support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was sponsored by the European Union Seventh Framework Programme in the SEAFRONT project [grant agreement 614034]; and the Netherlands Organisation for Scientific Research (NWO) [project number SH-023-15].