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Wake behind a three-dimensional dry transom stern. Part 1: Flow structure and large-scale air entrainment

Wake behind a three-dimensional dry transom stern. Part 1: Flow structure and large-scale air entrainment
Wake behind a three-dimensional dry transom stern. Part 1: Flow structure and large-scale air entrainment
We present high-resolution implicit large eddy simulation (iLES) of the turbulent air entraining flow in the wake of three-dimensional rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios B/D. We employ two-phase (air/water), time-dependent simulations utilizing conservative Volume-of-Fluid (cVOF) and Boundary Data Immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent corner wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (rectangular) geometry of the ship. We show that the flow structure in the air-water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with B/D. We determine that the average surface entrainment rate initially peaks at a location that scales with draft-Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the rectangular geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft-Froude number and geometry. In part 2 we examine the incompressible highly-variable density turbulence characteristics and turbulence closure modeling.
0022-1120
854-883
Hendrickson, Kelli
358d7339-2b4c-4b62-820f-a9be37434251
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Yue, Dick K.-P.
efbe9a39-3cdc-4381-8a65-e72b4a590935
Yu, Xiangming
6d8a3734-6d41-40e4-99e5-a4f2a10aa794
Hendrickson, Kelli
358d7339-2b4c-4b62-820f-a9be37434251
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Yue, Dick K.-P.
efbe9a39-3cdc-4381-8a65-e72b4a590935
Yu, Xiangming
6d8a3734-6d41-40e4-99e5-a4f2a10aa794

Hendrickson, Kelli, Weymouth, Gabriel, Yue, Dick K.-P. and Yu, Xiangming (2019) Wake behind a three-dimensional dry transom stern. Part 1: Flow structure and large-scale air entrainment. Journal of Fluid Mechanics, 875, 854-883. (doi:10.1017/jfm.2019.505).

Record type: Article

Abstract

We present high-resolution implicit large eddy simulation (iLES) of the turbulent air entraining flow in the wake of three-dimensional rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios B/D. We employ two-phase (air/water), time-dependent simulations utilizing conservative Volume-of-Fluid (cVOF) and Boundary Data Immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent corner wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (rectangular) geometry of the ship. We show that the flow structure in the air-water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with B/D. We determine that the average surface entrainment rate initially peaks at a location that scales with draft-Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the rectangular geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft-Froude number and geometry. In part 2 we examine the incompressible highly-variable density turbulence characteristics and turbulence closure modeling.

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hendrickson_2019 - Accepted Manuscript
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Accepted/In Press date: 20 June 2019
e-pub ahead of print date: 26 July 2019
Published date: 25 September 2019

Identifiers

Local EPrints ID: 431952
URI: http://eprints.soton.ac.uk/id/eprint/431952
ISSN: 0022-1120
PURE UUID: 4de67493-18be-46a5-8021-1c8c8e29f9d1
ORCID for Gabriel Weymouth: ORCID iD orcid.org/0000-0001-5080-5016

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Date deposited: 24 Jun 2019 16:30
Last modified: 18 Feb 2021 17:21

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Author: Kelli Hendrickson
Author: Dick K.-P. Yue
Author: Xiangming Yu

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