The University of Southampton
University of Southampton Institutional Repository

Near-wall flow development after a step change in surface roughness

Near-wall flow development after a step change in surface roughness
Near-wall flow development after a step change in surface roughness
An experimental study of the initial flow field downstream of a step change in surface roughness is presented. The roughness length of the downstream surface was approximately tenfold that of the upstream roughness and, unlike all previous studies, attention was concentrated on the roughness sublayer region beneath the inertial (log-law) region. The experiments were conducted at a boundary layer Reynolds number of about 6 × 104 (based on layer thickness and free-stream velocity) and around a longitudinal location where the (downstream) roughness length, zo2, was about 1% of the boundary-layer thickness at the roughness change point. The thickness of the roughness sublayer was found for the two roughness. It was observed that the vertical profiles of mean velocity and turbulence characteristics started to show similarity after about 160z02 downstream of the roughness change. The presence of a shear stress overshoot is shown to depend strongly on the precise location (with respect to the roughness elements) at which the measurements are made and the thickness of the equilibrium layer is shown to be very sensitive to the way it is defined. It is demonstrated that the growing equilibrium layer has first to encompass the roughness sublayer before any thickness of inertial sublayer can be developed. It follows that, in some practical cases, like flows across some urban environments, the latter (log-law) region may never exist at all.
roughness change, roughness sublayer, wind tunnel
0006-8314
411-432
Cheng, H.
de8f13f3-1d85-48b6-a9da-54fa69571688
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61
Cheng, H.
de8f13f3-1d85-48b6-a9da-54fa69571688
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61

Cheng, H. and Castro, I.P. (2002) Near-wall flow development after a step change in surface roughness. Boundary-Layer Meteorology, 105 (3), 411-432.

Record type: Article

Abstract

An experimental study of the initial flow field downstream of a step change in surface roughness is presented. The roughness length of the downstream surface was approximately tenfold that of the upstream roughness and, unlike all previous studies, attention was concentrated on the roughness sublayer region beneath the inertial (log-law) region. The experiments were conducted at a boundary layer Reynolds number of about 6 × 104 (based on layer thickness and free-stream velocity) and around a longitudinal location where the (downstream) roughness length, zo2, was about 1% of the boundary-layer thickness at the roughness change point. The thickness of the roughness sublayer was found for the two roughness. It was observed that the vertical profiles of mean velocity and turbulence characteristics started to show similarity after about 160z02 downstream of the roughness change. The presence of a shear stress overshoot is shown to depend strongly on the precise location (with respect to the roughness elements) at which the measurements are made and the thickness of the equilibrium layer is shown to be very sensitive to the way it is defined. It is demonstrated that the growing equilibrium layer has first to encompass the roughness sublayer before any thickness of inertial sublayer can be developed. It follows that, in some practical cases, like flows across some urban environments, the latter (log-law) region may never exist at all.

Full text not available from this repository.

More information

Published date: 2002
Keywords: roughness change, roughness sublayer, wind tunnel

Identifiers

Local EPrints ID: 22189
URI: http://eprints.soton.ac.uk/id/eprint/22189
ISSN: 0006-8314
PURE UUID: 7b97b5dc-53b1-4d32-9a59-dec6aef853fb

Catalogue record

Date deposited: 22 Mar 2006
Last modified: 14 Sep 2021 17:56

Export record

Contributors

Author: H. Cheng
Author: I.P. Castro

University divisions

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 http://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.

×