scholarly journals Parameterization of Wave-Induced Mixing Using the Large Eddy Simulation (LES) (I)

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 207 ◽  
Author(s):  
Haili Wang ◽  
Changming Dong ◽  
Yongzeng Yang ◽  
Xiaoqian Gao
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Global Climate Models ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wave Induced

Turbulent motions in the thin ocean surface boundary layer control exchanges of momentum, heat and trace gases between the atmosphere and ocean. However, present parametric equations of turbulent motions that are applied to global climate models result in systematic or substantial errors in the ocean surface boundary layer. Significant mixing caused by surface wave processes is missed in most parametric equations. A Large Eddy Simulation model is applied to investigate the wave-induced mixed layer structure. In the wave-averaged equations, wave effects are calculated as Stokes forces and breaking waves. To examine the effects of wave parameters on mixing, a series of wave conditions with varying wavelengths and heights are used to drive the model, resulting in a variety of Langmuir turbulence and wave breaking outcomes. These experiments suggest that wave-induced mixing is more sensitive to wave heights than to the wavelength. A series of numerical experiments with different wind intensities-induced Stokes drifts are also conducted to investigate wave-induced mixing. As the wind speed increases, the influence depth of Langmuir circulation deepens. Additionally, it is observed that breaking waves could destroy Langmuir cells mainly at the sea surface, rather than at deeper layers.

LESbrary: A library of large eddy simulation data for the calibration and uncertainty quantification of ocean surface boundary layer turbulence parameterizations

2021 ◽  
Author(s):  
Gregory Wagner ◽  
Andre Souza ◽  
Adeline Hillier ◽  
Ali Ramadhan ◽  
Raffaele Ferrari
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Ocean Surface ◽  
Limited Area ◽  
Surface Boundary ◽  
Model Errors ◽  
Surface Boundary Layer ◽  
Large Eddy ◽  
Free Parameters

<p>Parameterizations of turbulent mixing in the ocean surface boundary layer (OSBL) are key Earth System Model (ESM) components that modulate the communication of heat and carbon between the atmosphere and ocean interior. OSBL turbulence parameterizations are formulated in terms of unknown free parameters estimated from observational or synthetic data. In this work we describe the development and use of a synthetic dataset called the “LESbrary” generated by a large number of idealized, high-fidelity, limited-area large eddy simulations (LES) of OSBL turbulent mixing. We describe how the LESbrary design leverages a detailed understanding of OSBL conditions derived from observations and large scale models to span the range of realistically diverse physical scenarios. The result is a diverse library of well-characterized “synthetic observations” that can be readily assimilated for the calibration of realistic OSBL parameterizations in isolation from other ESM model components. We apply LESbrary data to calibrate free parameters, develop prior estimates of parameter uncertainty, and evaluate model errors in two OSBL parameterizations for use in predictive ESMs.</p>

scholarly journals The Role of Whitecapping in Thickening the Ocean Surface Boundary Layer

2015 ◽  
Vol 45 (8) ◽  
pp. 2006-2024 ◽  
Author(s):  
Gregory P. Gerbi ◽  
Samuel E. Kastner ◽  
Genevieve Brett
Keyword(s):  
Boundary Layer ◽  
Initial Conditions ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Length Scale ◽  
Surface Boundary ◽  
Transfer Velocity ◽  
Surface Boundary Layer ◽  
Turbulent Length Scale ◽  
Shear Production

AbstractThe effects of wind-driven whitecapping on the evolution of the ocean surface boundary layer are examined using an idealized one-dimensional Reynolds-averaged Navier–Stokes numerical model. Whitecapping is parameterized as a flux of turbulent kinetic energy through the sea surface and through an adjustment of the turbulent length scale. Simulations begin with a two-layer configuration and use a wind that ramps to a steady stress. This study finds that the boundary layer begins to thicken sooner in simulations with whitecapping than without because whitecapping introduces energy to the base of the boundary layer sooner than shear production does. Even in the presence of whitecapping, shear production becomes important for several hours, but then inertial oscillations cause shear production and whitecapping to alternate as the dominant energy sources for mixing. Details of these results are sensitive to initial and forcing conditions, particularly to the turbulent length scale imposed by breaking waves and the transfer velocity of energy from waves to turbulence. After 1–2 days of steady wind, the boundary layer in whitecapping simulations has thickened more than the boundary layer in simulations without whitecapping by about 10%–50%, depending on the forcing and initial conditions.

scholarly journals Comments on “Langmuir Turbulence and Surface Heating in the Ocean Surface Boundary Layer”

2018 ◽  
Vol 48 (2) ◽  
pp. 455-458 ◽  
Author(s):  
Yign Noh ◽  
Yeonju Choi
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Large Eddy Simulations ◽  
Surface Heating ◽  
Length Scale ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer ◽  
Obukhov Length ◽  
Large Eddy

AbstractUsing large-eddy simulations (LES) it is shown that the depth of a diurnal thermocline h should be scaled by the Zilitinkevich scale LZ, not by the Monin–Obukhov length scale LMO, contrary to the proposition by Pearson et al. Their argument to explain the slower increase of h than LMO using the effect of the preexisting thermocline is also invalid.

scholarly journals Lagrangian Investigation of Wave-Driven Turbulence in the Ocean Surface Boundary Layer

2019 ◽  
Vol 49 (2) ◽  
pp. 409-429 ◽  
Author(s):  
Tobias Kukulka ◽  
Fabrice Veron
Keyword(s):  
Boundary Layer ◽  
Turbulent Transport ◽  
Ocean Surface ◽  
Inertial Subrange ◽  
Breaking Wave ◽  
Surface Boundary ◽  
Lagrangian Analysis ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Eddy Simulation

AbstractTurbulent processes in the ocean surface boundary layer (OSBL) play a key role in weather and climate systems. This study explores a Lagrangian analysis of wave-driven OSBL turbulence, based on a large-eddy simulation (LES) model coupled to a Lagrangian stochastic model (LSM). Langmuir turbulence (LT) is captured by Craik–Leibovich wave forcing that generates LT through the Craik–Leibovich type 2 (CL2) mechanism. Breaking wave (BW) effects are modeled by a surface turbulent kinetic energy flux that is constrained by wind energy input to surface waves. Unresolved LES subgrid-scale (SGS) motions are simulated with the LSM to be energetically consistent with the SGS model of the LES. With LT, Lagrangian autocorrelations of velocities reveal three distinct turbulent time scales: an integral, a dispersive mixing, and a coherent structure time. Coherent structures due to LT result in relatively narrow peaks of Lagrangian frequency velocity spectra. With and without waves, the high-frequency spectral tail is consistent with expectations for the inertial subrange, but BWs substantially increase spectral levels at high frequencies. Consistently, over short times, particle-pair dispersion results agree with the Richardson–Obukhov law, and near-surface dispersion is significantly enhanced because of BWs. Over longer times, our dispersion results are consistent with Taylor dispersion. In this case, turbulent diffusivities are substantially larger with LT in the crosswind direction, but reduced in the along-wind direction because of enhanced turbulent transport by LT that reduces mean Eulerian shear. Our results indicate that the Lagrangian analysis framework is effective and physically intuitive to characterize OSBL turbulence.

Large Eddy Simulation of Tandem Blade Stator Cascades

2017 ◽  
Author(s):  
Pratik Mitra ◽  
Jahnavi Kantharaju ◽  
Rohan Rayan ◽  
Joseph Mathew
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Immersed Boundary ◽  
Surface Boundary ◽  
Suction Surface ◽  
Surface Boundary Layer ◽  
Substantial Impact ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rapid Transition

Large eddy simulations of tandem blade compressor cascades have been performed with an explicit filtering method. A low speed case was simulated using the public domain code Incompact3d which solves incompressible flow with an immersed boundary method for embedded solid bodies, obviating the effort expended on preparing good quality meshes around blading. The LES successfully captures transition on the front blade and yields a significantly different loading compared with RANS solutions obtained before. The less substantial impact on the rear blade is traced to rapid transition forced by the turbulent wake of the front blade. LES with a refined grid was found to shorten the transition width due to the crucial role of small scales during transition. A complementary study with an in-house compressible LES solver was conducted for a transonic tandem cascade at the inlet Mach number of 0.89. Flow expands around the leading edge of the front blade and is terminated by a shock which interacts with the suction surface boundary layer. The beneficial effect of tandem blading was found to be achieved by limiting this separation. The shock-induced separation also marks a rapid transition of the suction surface boundary layer that is readily captured in the LES, showing pre-transitional streaks, but could prove difficult even for current transition-sensitive RANS.

Ocean Surface Boundary Layer Response to Abruptly Turning Winds

2021 ◽  
Author(s):  
Xingchi Wang ◽  
Tobias Kukulka
Keyword(s):  
Boundary Layer ◽  
Wave Model ◽  
Ocean Surface ◽  
Stokes Drift ◽  
Navier Stokes ◽  
Surface Boundary ◽  
Navier Stokes Equation ◽  
Surface Boundary Layer ◽  
Eddy Simulation ◽  
Budget Analysis

AbstractTurbulence driven by wind and waves controls the transport of heat, momentum, and matter in the ocean surface boundary layer (OSBL). For realistic ocean conditions, winds and waves are often neither aligned nor constant, for example, when winds turn rapidly. Based on a Large Eddy Simulation (LES) method, which captures shear-driven turbulence (ST) and Langmuir turbulence (LT) driven by the Craik-Leibovich vortex force, we investigate the OSBL response to abruptly turning winds. We design idealized LES experiments, whose winds are initially constant to equilibrate OSBL turbulence before abruptly turning 90° either cyclonically or anticyclonically. The transient Stokes drift for LT is estimated from a spectral wave model. The OSBL response includes three successive stages that follow the change in direction. During stage 1, turbulent kinetic energy (TKE) decreases due to reduced TKE production. Stage 2 is characterized by TKE increasing with TKE shear production recovering and exceeding TKE dissipation. Transient TKE levels may exceed their stationary values due to inertial resonance and non-equilibrium turbulence. Turbulence relaxes to its equilibrium state at stage 3, but LT still adjusts due to slowly developing waves. During stages 1 and 2, greatly misaligned wind and waves lead to Eulerian TKE production exceeding Stokes TKE production. A Reynolds stress budget analysis and Reynolds-averaged Navier-Stokes equation models indicate that Stokes production furthermore drives the OSBL response. The Coriolis effects result in asymmetrical OSBL responses to wind turning directions. Our results suggest that transient wind conditions play a key role in understanding realistic OSBL dynamics.

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