Ridge-induced secondary flows in wall turbulence

Abstract

Many rough surfaces in engineering and environmental flows are spatially heterogeneous in the cross-stream (or spanwise) direction and may contain a range of different surface length scales. In the special case when the dominant spanwise surface length scale is on the order of the largest scales of the flow, local delta-scale secondary flows are formed.

There has been a growing interest in such surface-induced secondary flows as they are observed in many practical engineering applications. Examples include turbine blades ablated from foreign debris ingestion, bio-fouled ship hulls and flow control applications , as well as environmental flows such as river flows with applications in flood management and sediment transport. In all of these applications the resulting effect is a significant drag increase experienced by the surface.

In research applications surface-induced secondary flows can be generated with simplified surfaces made up of spanwise height variations, usually referred to as ridges, spaced approximately delta apart. A significant amount of research has been dedicated to understanding the effect the ridge geometry and surface configuration has on these large-scale vortical structures. However, experimental studies have generally been limited to low-to-modest Reynolds numbers mostly in turbulent boundary layers.

This body of work aims to experimentally investigate and characterise the mean flow, turbulent statistics and turbulent structure of ridge-induced secondary flows, with focus on a wider range of Reynolds numbers as well as different types of wall-bounded turbulent flows.

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Identifiers

ORCID for Mattias Nilsson-Takeuchi: orcid.org/0000-0002-2071-1075

ORCID for Bharath Ganapathisubramani: orcid.org/0000-0001-9817-0486

ORCID for Christina Vanderwel: orcid.org/0000-0002-5114-8377

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