A rough recovery
A rough recovery
The development of turbulent boundary layers (TBLs) over streamwise homogeneous roughness is well understood in the fully rough regime. However, while step changes in surface roughness (smooth-to-rough or rough-to-smooth) have been studied, the streamwise fetch length required for the TBL to return to equilibrium remains unclear. In addition, the use of the equivalent sand-grain roughness height, k
s, to describe non-equilibrium conditions following a step change has not been thoroughly evaluated. This work builds on the main results of [1], which showed that the minimum fetch length for equilibrium recovery after a step change in roughness is L ≈ 20δ
2, and that the equivalent sand-grain roughness, k
s, provides a useful model for the development of the internal layer. Extending this framework, we present new findings on the influence of surface geometry, physical roughness height and orientation, demonstrating that these factors do not affect the recovery of the mean flow: in all cases, equilibrium was reached within a fetch length range of 10-15δ
2, regardless of the roughness type.
Formichetti, Martina
4d5540eb-d793-4400-bcdf-322a66281095
Kwong, Ashley Lynn
c8beaadd-ecd3-43aa-aea7-af5a8ca3ebe6
Symon, Sean
2e1580c3-ba27-46e8-9736-531099f3d850
Ganapathisubramani, Bharath
5e69099f-2f39-4fdd-8a85-3ac906827052
2026
Formichetti, Martina
4d5540eb-d793-4400-bcdf-322a66281095
Kwong, Ashley Lynn
c8beaadd-ecd3-43aa-aea7-af5a8ca3ebe6
Symon, Sean
2e1580c3-ba27-46e8-9736-531099f3d850
Ganapathisubramani, Bharath
5e69099f-2f39-4fdd-8a85-3ac906827052
Formichetti, Martina, Kwong, Ashley Lynn, Symon, Sean and Ganapathisubramani, Bharath
(2026)
A rough recovery.
11th iTi conference on turbulence 2025, , Bertinoro, Italy.
27 - 30 Jul 2025.
(doi:10.1088/1742-6596/3173/1/012019).
Record type:
Conference or Workshop Item
(Paper)
Abstract
The development of turbulent boundary layers (TBLs) over streamwise homogeneous roughness is well understood in the fully rough regime. However, while step changes in surface roughness (smooth-to-rough or rough-to-smooth) have been studied, the streamwise fetch length required for the TBL to return to equilibrium remains unclear. In addition, the use of the equivalent sand-grain roughness height, k
s, to describe non-equilibrium conditions following a step change has not been thoroughly evaluated. This work builds on the main results of [1], which showed that the minimum fetch length for equilibrium recovery after a step change in roughness is L ≈ 20δ
2, and that the equivalent sand-grain roughness, k
s, provides a useful model for the development of the internal layer. Extending this framework, we present new findings on the influence of surface geometry, physical roughness height and orientation, demonstrating that these factors do not affect the recovery of the mean flow: in all cases, equilibrium was reached within a fetch length range of 10-15δ
2, regardless of the roughness type.
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Published date: 2026
Venue - Dates:
11th iTi conference on turbulence 2025, , Bertinoro, Italy, 2025-07-27 - 2025-07-30
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Local EPrints ID: 510697
URI: http://eprints.soton.ac.uk/id/eprint/510697
PURE UUID: 088917f7-b9f0-4903-8020-deac2555e093
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Date deposited: 16 Apr 2026 17:09
Last modified: 02 Jun 2026 02:06
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Author:
Martina Formichetti
Author:
Ashley Lynn Kwong
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