Abstract:

Langmuir turbulence in the coastal ocean is driven by winds and waves and is characterized by Langmuir cells (LCs) that can span the full depth of the water column in unstratified settings. A solution strategy based on Reynolds averaging is introduced, relying on the coherency and persistence of full-depth LCs. Here these cells are resolved by the Reynolds-averaged formulation, treated as a secondary component to the wind and/or pressure gradient-driven primary flow. Two uniform depth simulations performed with the Reynolds-averaged formulation are submitted following the large-eddy simulation setup of Tejada-Martínez & Grosch (2007). Both cases are characterized by a turbulent Langmuir number (Lat) of 0.7 (see Tejada-Martinez and Grosch, 2007) and a wavelength of 6H and 3H (where H is the water column depth), parameters related to the wind and wave forcing conditions in the simulations. The case with the wavelength of 6*H and Lat = 0.7 corresponds to wind stress of 0.1 N/m^2, the significant wavelength of 90 m, and significant wave amplitude of 0.6 m measured in the field observations of full-depth Langmuir cells by Gargett & Wells (2007) in 15 meters depth. The variable depth simulation consists of a domain with depth varying between H=15 meters and H=7.5 meters over a 1 km distance along the x-direction. The depth is constant along the y-direction. The wind and waves are aligned in the y-direction. The wind stress, the wave amplitude, and the wavelength are fixed at 0.1 N/m^2, 0.6 m and 90 m (6*H = 6*15 m). The wave frequency is computed from the dispersion relation. The dataset consists of three-dimensional fields of velocity, turbulent kinetic energy, and epsilon values as a function of time for the uniform depth cases (160, 320, 480, and 640 minutes and 14 hours) and variable depth cases (1450, 290, 435, and 580 minutes). A detailed Readme document describes the model domain, forcing, and solution methods and provides snapshots of vertical velocity fluctuations.

Suggested Citation:

Tejada-Martínez, A. E., Juan Penaloza-Gutierrez, Anthony Perez, and Seyed Zeidi. 2021. A Reynolds-averaged simulation of costal Langmuir cells in a constant depth and variable depth water column. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/DQF7VRHT

Purpose:

To understand the dynamics of Langmuir supercells engulfing an unstratified shallow water column and how the larger Langmuir scales interact with variable topography.

Data Parameters and Units:

Data is dimensionless. To dimensionalize, dimensionless (or model) velocities should be multiplied by a characteristic mean flow velocity of 0.17215 m/s. Dimensionless (or model) lengths should be multiplied by a characteristic length scale of 7.5 m. Nodenumber [enum], x-coordinate, y-coordinate, z-coordinate, z-velocity-ms-1 [m/s], x-velocity-ms-1 [m/s], y-velocity-ms-1 [m/s], tke-m2s-2 (turbulent kinetic energy, [m^2/s]), epsilon-m2s-3 (turbulent energy dissipation rate, [m^2/s^3]).

Methods:

A solution strategy based on the Reynolds-averaged Navier-Stokes (RANS) equations is used to resolve the largest of the Langmuir scales, given their coherency and persistence. All simulations were performed with a commercial computational fluid dynamic code ANSYS FLUENT. The model domain is 125 m x 942 m x 15 m with 128 x 320 x 64 elements (crosswind, downwind, and vertical). It includes a no-slip bottom, X and Y periodicity, and a rigid-lid top surface wind-sheared in the Y direction. Further details and illustrations are provided in the accompanying Readme document.

Provenance and Historical References:

Gargett, Ann E., and Judith R. Wells (2007). Langmuir turbulence in shallow water. Part 1. Observations. Journal of Fluid Mechanics, 576, 27–61. doi:10.1017/s0022112006004575 Tejada-Martinez, A. E., and C. E. Grosch (2007). Langmuir turbulence in shallow water. Part 2. Large-eddy simulation. Journal of Fluid Mechanics, 576, 63–108. doi:10.1017/s0022112006004587

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