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Characteristics of drag due to streamwise inhomogeneous roughness

Characteristics of drag due to streamwise inhomogeneous roughness
Characteristics of drag due to streamwise inhomogeneous roughness
Characteristics of the skin friction due to streamwise inhomogeneous roughness are investigated by modelling it in a simplified manner using step changes in equivalent sand grain roughness height 푘푠, denoted as P (푘푠 = 81.25 µm), Q (푘푠 = 325.00 µm) and R (푘푠 = 568.75 µm). The selected 푘푠 values represent the common ship-hull roughness, i.e., from light slime to about small calcareous fouling. RANS simulations are performed to study the friction characteristics of various rough surfaces formed by a trio combination of P,Q and R roughnesses on flat plates with streamwise lengths of 30, 60, 120 and 240 m. The three combinations of roughnesses formeither homogeneous (PPP, QQQ or RRR) or inhomogeneous (PQR, PRQ, QPR, etc.) rough walled turbulent boundary layer flow. A step change in roughness height results in a sudden change of the local skin friction coefficient in the form of overshoot or undershoot, followed by a relaxation where the inhomogeneous local skin friction is slowly returning to the homogeneous local one. The sequence of roughness arrangement in a streamwise in homogeneous roughness pattern plays a key role in the resulting overall skin friction with value increasing in the following order: PQR < PRQ < QPR < QRP < RPQ < RQP. The similarity laws hold for both homogeneous and inhomogeneous rough surfaces.
Biofouling, Energy efficiency, Inhomogeneous roughness, RANS simulations, Similarity laws, Skin friction
0029-8018
Suastika, K
f8949583-64f0-4bad-9fea-72c331c08815
Hakim, M L
bb41938a-dc30-4fe8-8c43-d835fec8601c
Nugroho, B
b2ac9cc0-24f5-4652-bf55-eb2c4ee5a86a
Nasirudin, A
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Utama, I K A P
ae72d50b-7977-4d9f-a912-352f3b7378ce
Monty, J P
cae94b74-92b6-43cc-b278-5604636e0b3e
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Suastika, K
f8949583-64f0-4bad-9fea-72c331c08815
Hakim, M L
bb41938a-dc30-4fe8-8c43-d835fec8601c
Nugroho, B
b2ac9cc0-24f5-4652-bf55-eb2c4ee5a86a
Nasirudin, A
b0678f8c-6ae5-46ac-82ce-0e91522b7d3c
Utama, I K A P
ae72d50b-7977-4d9f-a912-352f3b7378ce
Monty, J P
cae94b74-92b6-43cc-b278-5604636e0b3e
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Suastika, K, Hakim, M L, Nugroho, B, Nasirudin, A, Utama, I K A P, Monty, J P and Ganapathisubramani, Bharathram (2021) Characteristics of drag due to streamwise inhomogeneous roughness. Ocean Engineering, 223, [108632]. (doi:10.1016/j.oceaneng.2021.108632).

Record type: Article

Abstract

Characteristics of the skin friction due to streamwise inhomogeneous roughness are investigated by modelling it in a simplified manner using step changes in equivalent sand grain roughness height 푘푠, denoted as P (푘푠 = 81.25 µm), Q (푘푠 = 325.00 µm) and R (푘푠 = 568.75 µm). The selected 푘푠 values represent the common ship-hull roughness, i.e., from light slime to about small calcareous fouling. RANS simulations are performed to study the friction characteristics of various rough surfaces formed by a trio combination of P,Q and R roughnesses on flat plates with streamwise lengths of 30, 60, 120 and 240 m. The three combinations of roughnesses formeither homogeneous (PPP, QQQ or RRR) or inhomogeneous (PQR, PRQ, QPR, etc.) rough walled turbulent boundary layer flow. A step change in roughness height results in a sudden change of the local skin friction coefficient in the form of overshoot or undershoot, followed by a relaxation where the inhomogeneous local skin friction is slowly returning to the homogeneous local one. The sequence of roughness arrangement in a streamwise in homogeneous roughness pattern plays a key role in the resulting overall skin friction with value increasing in the following order: PQR < PRQ < QPR < QRP < RPQ < RQP. The similarity laws hold for both homogeneous and inhomogeneous rough surfaces.

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suastika-et-al-rev_2_unmarked_latex - Accepted Manuscript
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Published date: 13 January 2021
Keywords: Biofouling, Energy efficiency, Inhomogeneous roughness, RANS simulations, Similarity laws, Skin friction

Identifiers

Local EPrints ID: 446172
URI: http://eprints.soton.ac.uk/id/eprint/446172
ISSN: 0029-8018
PURE UUID: 4fcd3598-f6dd-4550-9bdc-bffd6ea5aeb2
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 26 Jan 2021 17:30
Last modified: 22 Nov 2021 02:59

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Contributors

Author: K Suastika
Author: M L Hakim
Author: B Nugroho
Author: A Nasirudin
Author: I K A P Utama
Author: J P Monty

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