The University of Southampton
University of Southampton Institutional Repository

Characteristics of turbulent boundary layers over smooth surfaces with spanwise heterogeneities

Characteristics of turbulent boundary layers over smooth surfaces with spanwise heterogeneities
Characteristics of turbulent boundary layers over smooth surfaces with spanwise heterogeneities
An experimental investigation of a turbulent boundary layer flow over a heterogeneous surface is carried out to examine the mean flow and turbulence characteristics, and to document the variation of skin-friction that might affect the applicability of traditional scaling and similarity laws. The heterogeneity is imposed along the spanwise direction and consists of streamwise-aligned smooth raised strips whose spanwise spacing S is comparable to the boundary layer thickness (S~ = O(1)). Single-point velocity measurements alongside direct skin-friction measurements are used to examine the validity of Townsend's similarity hypothesis. The skin-friction coefficients reveal that the drag of the heterogeneous surface increased up to 35% compared to a smooth wall, while velocity measurements reveal the existence of a log-layer but with a zero-plane displacement and a roughness function that vary across the spanwise direction. Lack of collapse in the outer region of the mean velocity and variance profiles is attributed to the secondary flows induced by the heterogeneous surfaces. Additionally, the lack of similarity also extends to the spectra across all scales in the near-wall region with a gradual collapse at small wavelengths for increasing S. This suggests that the effect of surface heterogeneity is not necessarily felt at the smaller scales other than to reorganise their presence through turbulent transport.
0022-1120
516-543
Medjnoun, Takfarinas
878ec432-7360-48ad-bce1-c7a1dc2191cb
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Medjnoun, Takfarinas
878ec432-7360-48ad-bce1-c7a1dc2191cb
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Medjnoun, Takfarinas, Vanderwel, Christina and Ganapathisubramani, Bharathram (2018) Characteristics of turbulent boundary layers over smooth surfaces with spanwise heterogeneities. Journal of Fluid Mechanics, 838, 516-543. (doi:10.1017/jfm.2017.849).

Record type: Article

Abstract

An experimental investigation of a turbulent boundary layer flow over a heterogeneous surface is carried out to examine the mean flow and turbulence characteristics, and to document the variation of skin-friction that might affect the applicability of traditional scaling and similarity laws. The heterogeneity is imposed along the spanwise direction and consists of streamwise-aligned smooth raised strips whose spanwise spacing S is comparable to the boundary layer thickness (S~ = O(1)). Single-point velocity measurements alongside direct skin-friction measurements are used to examine the validity of Townsend's similarity hypothesis. The skin-friction coefficients reveal that the drag of the heterogeneous surface increased up to 35% compared to a smooth wall, while velocity measurements reveal the existence of a log-layer but with a zero-plane displacement and a roughness function that vary across the spanwise direction. Lack of collapse in the outer region of the mean velocity and variance profiles is attributed to the secondary flows induced by the heterogeneous surfaces. Additionally, the lack of similarity also extends to the spectra across all scales in the near-wall region with a gradual collapse at small wavelengths for increasing S. This suggests that the effect of surface heterogeneity is not necessarily felt at the smaller scales other than to reorganise their presence through turbulent transport.

Text Main document - Accepted Manuscript
Download (2MB)

More information

Accepted/In Press date: 9 November 2017
e-pub ahead of print date: 18 January 2018
Published date: 10 March 2018

Identifiers

Local EPrints ID: 415626
URI: https://eprints.soton.ac.uk/id/eprint/415626
ISSN: 0022-1120
PURE UUID: 82aa331c-cb54-4d04-a31f-0efcbb79b45b
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 16 Nov 2017 17:30
Last modified: 20 Jul 2018 04:01

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×