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Research Papers: Ocean Engineering

Turbulence Characteristics of Flow Under Combined Wave–Current Motion

[+] Author and Article Information
Santosh Kumar Singh

Fluid Mechanics and Hydraulic Laboratory,
Department of Aerospace Engineering
and Applied Mechanics,
Indian Institute of Engineering
Science and Technology (IIEST),
Shibpur, Howrah 711103, India
e-mail: fmsks84@gmail.com

Koustuv Debnath

Professor
Fluid Mechanics and Hydraulic Laboratory,
Department of Aerospace Engineering
and Applied Mechanics,
Indian Institute of Engineering
Science and Technology (IIEST),
Shibpur, Howrah 711103, India
e-mail: debnath_koustuv@yahoo.com

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received January 4, 2016; final manuscript received October 15, 2016; published online January 31, 2017. Assoc. Editor: Celso P. Pesce.

J. Offshore Mech. Arct. Eng 139(2), 021102 (Jan 31, 2017) (8 pages) Paper No: OMAE-16-1001; doi: 10.1115/1.4035139 History: Received January 04, 2016; Revised October 15, 2016

This paper describes an experimental study carried out in a laboratory flume with a smooth surface to investigate the effect of a surface wave on unidirectional current. The measured velocity data were analyzed within the framework of the phase averaging for combined wave–current flow and verified by velocity equations based on the phase-averaged Prandtl momentum-transfer theory. The results highlight the changes induced on the mean velocity profile, turbulence intensity, and Reynolds shear stress in a plane of symmetry due to the superposition of surface waves of different frequencies. Modifications in the mean velocities, the turbulence intensities, and the Reynolds shear stresses with respect to the current-only flow are explored. As the frequency of the surface waves in unidirectional current changes, the results show variations in the mean flow and in the turbulence statistics that may affect the local sediment mobility in the coastal region.

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Figures

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Fig. 1

Schematic diagram of the flume

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Fig. 2

Plot of the normalized error for the mean flow at measurement section

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Fig. 3

Normalized profile of (a) streamwise and bottom-normal mean velocities (û and ŵ), (b) streamwise turbulence intensity (Iu), (c) bottom-normal turbulence intensity (Iw), and (d) Reynolds shear stress (τ̂) based on present measurements on a flat surface. Here, the parameters are Bu = 1.9, Bw = 0.98, Cu = 1.04, and Cw = 0.51.

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Fig. 4

Normalized streamwise mean velocity profiles for combined wave–current flow. (a)–(c) represents velocity profiles f = 0.6, 1.5, and 2.5 Hz, respectively. Velocity profile for current-only is also presented for reference and the solid line represents the profile calculated by using Eqs. 10 and 11.

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Fig. 5

Vertical profiles of turbulence intensities for wave–current flow along with current-only is also presented for reference; (a) phase-averaged streamwise turbulent intensity and (b) phase-averaged bottom-normal turbulent intensity

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Fig. 6

Calculated mean phase-averaged Reynolds stress [14,18] profile for wave–current flow along with current-only is also presented for reference

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Fig. 7

Probability density function (PDF) of streamwise velocity component for both current only and wave-induced cases: (a) at z/h = 0.02, (b) at z/h = 0.10, and (c) at z/h = 0.6

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