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Mean flow of turbulent boundary layers over porous substrates

Mean flow of turbulent boundary layers over porous substrates
Mean flow of turbulent boundary layers over porous substrates
Mean-flow measurements of turbulent boundary layers over porous walls (permeable and rough) with varying pore size (s), permeability (K) and thickness (h) are presented across a wide range of friction Reynolds numbers (Reτ≈2000–18000) and permeability based Reynolds numbers (ReK≈1.5–60). The mean wall shear stress was determined using a floating element drag balance and the boundary layer profiles were acquired using hot-wire anemometry. Substrate permeability is shown to increase the magnitude of the mean velocity deficit. The use of a modified indicator function, assuming “universal” values for von Karman constant (κ=0.39) supports previous results where a strongly modified logarithmic region was observed. The indicator function was also used to estimate the zero-plane displacement (yd), the roughness function (ΔU+), and equivalent sandgrain roughness (ks). At high Reynolds numbers, the roughness function data collapses on to the Nikuradse's fully rough asymptote. However, at low roughness Reynolds numbers (k+s<100), we observe the flow to be transitionally rough, evolving with Nikuradse-type behavior. The equivalent sandgrain roughness ks for each substrate appears to include roughness and permeability contributions. These two contributions can be separated using data obtained from the same substrates with different thickness. This may allow us to model the porous wall as a combination of rough and permeable wall.
2469-990X
Blay esteban, Luis
b2b8781e-a741-436f-ba2a-cc475cd10834
Rodriguez-Lopez, Eduardo
8595fcd2-436b-4c93-81ca-58aab8a27bb8
Ferreira, Manuel A.
cee20499-8e29-4164-a7b2-a2f47c8e3579
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Blay esteban, Luis
b2b8781e-a741-436f-ba2a-cc475cd10834
Rodriguez-Lopez, Eduardo
8595fcd2-436b-4c93-81ca-58aab8a27bb8
Ferreira, Manuel A.
cee20499-8e29-4164-a7b2-a2f47c8e3579
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Blay esteban, Luis, Rodriguez-Lopez, Eduardo, Ferreira, Manuel A. and Ganapathisubramani, Bharathram (2022) Mean flow of turbulent boundary layers over porous substrates. Physical Review Fluids. (doi:10.1103/PhysRevFluids.7.094603).

Record type: Article

Abstract

Mean-flow measurements of turbulent boundary layers over porous walls (permeable and rough) with varying pore size (s), permeability (K) and thickness (h) are presented across a wide range of friction Reynolds numbers (Reτ≈2000–18000) and permeability based Reynolds numbers (ReK≈1.5–60). The mean wall shear stress was determined using a floating element drag balance and the boundary layer profiles were acquired using hot-wire anemometry. Substrate permeability is shown to increase the magnitude of the mean velocity deficit. The use of a modified indicator function, assuming “universal” values for von Karman constant (κ=0.39) supports previous results where a strongly modified logarithmic region was observed. The indicator function was also used to estimate the zero-plane displacement (yd), the roughness function (ΔU+), and equivalent sandgrain roughness (ks). At high Reynolds numbers, the roughness function data collapses on to the Nikuradse's fully rough asymptote. However, at low roughness Reynolds numbers (k+s<100), we observe the flow to be transitionally rough, evolving with Nikuradse-type behavior. The equivalent sandgrain roughness ks for each substrate appears to include roughness and permeability contributions. These two contributions can be separated using data obtained from the same substrates with different thickness. This may allow us to model the porous wall as a combination of rough and permeable wall.

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Accepted/In Press date: 2022
e-pub ahead of print date: 22 September 2022

Identifiers

Local EPrints ID: 470645
URI: http://eprints.soton.ac.uk/id/eprint/470645
ISSN: 2469-990X
PURE UUID: 30671ed1-bd50-4f07-8230-809f1a503309
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 17 Oct 2022 16:39
Last modified: 18 Oct 2022 01:42

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Contributors

Author: Luis Blay esteban
Author: Eduardo Rodriguez-Lopez
Author: Manuel A. Ferreira

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