Investigation of rough-wall turbulence over barnacle roughness with increasing solidity using direct numerical simulations

Sarakinos, S. and Busse, A. (2022) Investigation of rough-wall turbulence over barnacle roughness with increasing solidity using direct numerical simulations. Physical Review Fluids, 7(6), 064602. (doi: 10.1103/PhysRevFluids.7.064602)

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Abstract

Barnacle-type roughness can be considered as a hybrid-form of roughness that combines some of the topographical features of traditional regular rough surfaces composed of discrete roughness elements of uniform size and shape, and of irregular rough surfaces that exhibit features with a wide distribution of sizes and shapes, covering the surface with a random areal distribution. In this study, the influence of barnacle-type rough surfaces with increasing coverage on wall-bounded turbulence is investigated using direct numerical simulations of turbulent channel flow. The barnacle-type rough surfaces were generated with an algorithm that mimics the settlement behaviour of barnacles, and the set of seven different surfaces describe the evolution of barnacle fouling with increasing coverage ranging from a lightly fouled surface with small isolated barnacle clusters (10% coverage) to a surface that is fully covered by barnacles (85% coverage). The roughness function recovers the expected trend with frontal solidity, attaining its maximum at a frontal solidity of approximately 0.2. Mean flow, Reynolds stress, and dispersive stresses show signatures of the clustering of roughness features, i.e., the barnacle colonies, at low coverage. This is most distinct for the streamwise Reynolds stresses where a double peak is observed at the lowest coverage; the inner peak can be interpreted as a partial recovery of smooth-wall behaviour over the large connected unfouled sections of this surface. The flow over the rough surfaces is further investigated by a topographical characterisation of the blanketing layer, i.e., the effective shape of the rough surface `perceived’ by the outer flow. A linear relationship between the roughness function and the effective slope of the blanketing layer is observed.

Item Type:Articles
Additional Information:We gratefully acknowledge support by the United Kingdom Engineering and Physical Sciences Research Council (EPSRC) under grant number EP/P009875/1 and access to the United Kingdom's National HPC facility ARCHER hosted by EPCC Edinburgh.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Busse, Dr Angela and Sarakinos, Dr Sotirios
Authors: Sarakinos, S., and Busse, A.
College/School:College of Science and Engineering > School of Engineering
College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
Journal Name:Physical Review Fluids
Publisher:American Physical Society
ISSN:2469-990X
ISSN (Online):2469-990X
Published Online:16 June 2022
Copyright Holders:Copyright © 2022 American Physical Society
First Published:First published in Physical Review Fluids 7(6):064602
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
173614Surface-specific Moody diagram: A new paradigm to predict drag penalty of realistic rough surfaces with applications to maritime transportAngela BusseEngineering and Physical Sciences Research Council (EPSRC)EP/P009875/1ENG - Autonomous Systems & Connectivity