Large eddy simulation of the rotation effect on the ocean turbulence kinetic energy budget in the surface mixed layer

2014 ◽  
Vol 32 (5) ◽  
pp. 1198-1206
Author(s):  
Shuang Li ◽  
Jinbao Song ◽  
Hailun He
Keyword(s):  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Energy Budget ◽  
Surface Mixed Layer ◽  
Rotation Effect ◽  
Ocean Turbulence ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulence Kinetic Energy Budget

Large-Eddy Simulation of Deep-Cycle Turbulence in an Equatorial Undercurrent Model

2013 ◽  
Vol 43 (11) ◽  
pp. 2490-2502 ◽  
Author(s):  
Hieu T. Pham ◽  
Sutanu Sarkar ◽  
Kraig B. Winters
Keyword(s):  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Buoyancy Frequency ◽  
Surface Mixed Layer ◽  
Equatorial Undercurrent ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Model Components ◽  
Surface Buoyancy ◽  
Les Model

Abstract Dynamical processes leading to deep-cycle turbulence in the Equatorial Undercurrent (EUC) are investigated using a high-resolution large-eddy simulation (LES) model. Components of the model include a background flow similar to the observed EUC, a steady westward wind stress, and a diurnal surface buoyancy flux. An LES of a 3-night period shows the presence of narrowband isopycnal oscillations near the local buoyancy frequency N as well as nightly bursts of deep-cycle turbulence at depths well below the surface mixed layer, the two phenomena that have been widely noted in observations. The deep cycle of turbulence is initiated when the surface heating in the evening relaxes, allowing a region with enhanced shear and a gradient Richardson number Rig less than 0.2 to form below the surface mixed layer. The region with enhanced shear moves downward into the EUC and is accompanied by shear instabilities and bursts of turbulence. The dissipation rate during the turbulence bursts is elevated by up to three orders of magnitude. Each burst is preceded by westward-propagating oscillations having a frequency of 0.004–0.005 Hz and a wavelength of 314–960 m. The Rig that was marginally stable in this region decreases to less than 0.2 prior to the bursts. A downward turbulent flux of momentum increases the shear at depth and reduces Rig. Evolution of the deep-cycle turbulence includes Kelvin–Helmholtz-like billows as well as vortices that penetrate downward and are stretched by the EUC shear.

Modelling a simple mechanism for the formation of phytoplankton thin layers using large-eddy simulation: in situ growth

2020 ◽  
Vol 653 ◽  
pp. 77-90
Author(s):  
A Brereton ◽  
Y Noh ◽  
S Raasch
Keyword(s):  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Light Availability ◽  
Euphotic Zone ◽  
Thin Layers ◽  
Biophysical Model ◽  
Surface Mixed Layer ◽  
Eddy Simulation ◽  
Phytoplankton Communities ◽  
Large Eddy

A curious phenomenon found in phytoplankton communities is the forming of socalled thin layers, wherein phytoplankton biomass can stretch out kilometres in the horizontal but only a few metres in the vertical. These layers are typically found at the pycnocline, just below the surface mixed layer. Thin layers are usually attributed to a range of complex environmental and species-dependent factors. However, we believe that, given the frequency at which this phenomenon is observed, a simpler mechanism is at play. In this study, we found that phytoplankton thin layers can be attributed simply to a decreasing light availability with depth, when there is an abundance of nutrients in the euphotic zone and below the mixed layer. This mechanism was ascertained using a number of modelling approaches ranging in complexity from analytical solutions of a simple 1-dimensional plankton model to a 3-dimensional biophysical model incorporating large-eddy simulation. The conditions which, according to the results of our study, allow thin layers to form are ubiquitous in the coastal ocean and are therefore a likely candidate explanation as to why planktonic thin layers are so frequently observed.

Large Eddy Simulation Coupling Model For Small-scale Air-sea Interaction

2020 ◽  
Author(s):  
Danyi Sun ◽  
Shuang Li
Keyword(s):  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Turbulent Kinetic Energy ◽  
Energy Budget ◽  
Coupling Model ◽  
Small Scale ◽  
Langmuir Circulation ◽  
Turbulent Kinetic Energy Budget ◽  
Eddy Simulation ◽  
Large Eddy

<p>Atmosphere and ocean are two important factors that affect the earth's climate system, and their interaction is an important topic in the study. In view of the lack of turbulence scale analysis in the traditional large-scale air-sea coupling model, this paper uses the Parallelized Large-Eddy Simulation Model (PALM) to explore the effect of Langmuir circulation on air-sea flux and turbulent kinetic energy budget at a small scale, and conducts air-sea coupled simulation for atmospheric boundary layer (ABL) and ocean mixed layer (OML). The results show that the distribution of air-sea flux near the surface is greatly influenced by the Langmuir circulation, thus strengthening the ocean mixing. The pressure term in the turbulent kinetic energy budget of the ocean is greatly affected by the Langmuir circulation near the sea surface and weakens rapidly as the depth deepens. This study shows the application of the small-scale air-sea coupling model in the study of air-sea flux, which has certain significance for the study of small-scale air-sea interaction.</p>

Kinetic-energy-flux-constrained model using an artificial neural network for large-eddy simulation of compressible wall-bounded turbulence

2021 ◽  
Vol 932 ◽  
Author(s):  
Changping Yu ◽  
Zelong Yuan ◽  
Han Qi ◽  
Jianchun Wang ◽  
Xinliang Li ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Energy Flux ◽  
Mean Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Bounded Turbulence

Kinetic energy flux (KEF) is an important physical quantity that characterizes cascades of kinetic energy in turbulent flows. In large-eddy simulation (LES), it is crucial for the subgrid-scale (SGS) model to accurately predict the KEF in turbulence. In this paper, we propose a new eddy-viscosity SGS model constrained by the properly modelled KEF for LES of compressible wall-bounded turbulence. The new methodology has the advantages of both accurate prediction of the KEF and strong numerical stability in LES. We can obtain an approximate KEF by the tensor-diffusivity model, which has a high correlation with the real value. Then, using the artificial neural network method, the local ratios between the real KEF and the approximate KEF are accurately modelled. Consequently, the SGS model can be improved by the product of that ratio and the approximate KEF. In LES of compressible turbulent channel flow, the new model can accurately predict mean velocity profile, turbulence intensities, Reynolds stress, temperature–velocity correlation, etc. Additionally, for the case of a compressible flat-plate boundary layer, the new model can accurately predict some key quantities, including the onset of transitions and transition peaks, the skin-friction coefficient, the mean velocity in the turbulence region, etc., and it can also predict the energy backscatters in turbulence. Furthermore, the proposed model also shows more advantages for coarser grids.

scholarly journals Large-eddy simulation of turbulent flows over an urban building array with the ABLE-LBM and comparison with 3D MRI observed data sets

2020 ◽  
Author(s):  
Yansen Wang ◽  
Michael J. Benson
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Atmospheric Boundary Layer ◽  
Validation Study ◽  
Tall Building ◽  
Turbulent Wind ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Building Array

Abstract In this article we describe the details of an ABLE-LBM (Atmospheric Boundary Layer Environment-Lattice Boltzmann Model) validation study for urban building array turbulent flow simulations. The ABLE-LBM large-eddy simulation results were compared with a set of 3D magnetic resonance image (MRI) velocimetry data. The ABLE-LBM simulations used the same building layout and Reynolds numbers operated in the laboratory water channel. The building set-up was an evenly spaced orthogonal array of cubic buildings (height = H) with a central tall building (height = 3H) in the second row. Two building orientations, angled with 0°and 45° wind directions, were simulated with ABLE-LBM. The model produced horizontal and vertical fields of time-averaged velocity fields and compared well with the experimental results. The model also produced urban canyon flows and vortices at front and lee sides and over building tops that were similar in strength and location to the laboratory studies. The turbulent kinetic energy associated with these two wind directions were also presented in this simulation study. It is shown that the building array arrangement, especially the tall building, has a great effect on turbulent wind fields. There is a Karman vortex street on the lee side of the tall building. High turbulent intensity areas are associated with the vortex shedding motions at building edges. In addition, the wind direction is a very important factor for turbulent wind and kinetic energy distribution. This validation study indicated that ABLE-LBM is a viable simulation model for turbulent atmospheric boundary layer flows in the urban building array. The computational speed of ABLE-LBM using the GPU has shown that real-time LES simulation is realizable for a computational domain with several millions grid points.

scholarly journals The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

Minerals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 597 ◽  
Author(s):  
Lu Yang ◽  
Zhenna Zhu ◽  
Xin Qi ◽  
Xiaokang Yan ◽  
Haijun Zhang
Keyword(s):  
Fly Ash ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Rotation Speed ◽  
Coal Fly Ash ◽  
Stirred Tank ◽  
Turbulent Length Scale ◽  
Mineral Particles ◽  
Eddy Simulation ◽  
Large Eddy

Pulp preconditioning using a stirred tank as a pretreatment process is vital to the flotation system, which can be used to improve the flotation efficiency of mineral particles. The kinetic energy that is dissipated in the stirred tank could strengthen the interaction process between mineral particles and flotation reagents to improve the flotation efficiency in the presence of the preconditioning. In this paper, the effect of the conditioning speed on the coal fly ash flotation was investigated using numerical simulations and conditioning-flotation tests. The large eddy simulation coupled with the Smagorinsky-Lilly subgrid model was employed to simulate the turbulence flow field in the stirred tank, which was equipped with a six blade Rushton turbine. The impeller rotation was modelled using the sliding mesh. The simulation results showed that the large eddy simulation (LES) well matched the previous experimental data. The turbulence characteristics, such as the mean velocity, turbulent kinetic energy, power consumption and instantaneous structures of trailing vortices were analysed in detail. The turbulent length scale (η) decreased as the rotation speed increased, and the minimum value of η was almost unchanged when the rotation speed was more than 1200 rpm. The conditioning-flotation tests of coal fly ash were conducted using different conditioning speeds. The results showed that the removal of unburned carbon was greatly improved due to the strengthened turbulence in the stirred tank, and the optimal results were obtained with an LOI of 3.32%, a yield of 78.69% and an RUC of 80.89% when the conditioning speed was 1200 rpm.

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