scholarly journals Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations

2014 ◽  
Vol 372 (2018) ◽  
pp. 20130285 ◽  
Author(s):  
V. Kitsios ◽  
J. S. Frederiksen ◽  
M. J. Zidikheri
Keyword(s):  
Antarctic Circumpolar Current ◽  
Scaling Laws ◽  
Regression Method ◽  
Energy Spectra ◽  
Least Squares Regression ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Circumpolar Current ◽  
Jet Structure

Parametrizations of the subgrid eddy–eddy and eddy–meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T =504, which is equivalent to a resolution of 0.24 ° globally. A stochastic parametrization is used for the eddy–eddy interactions, and a linear deterministic parametrization for the eddy–meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, T R < T . A stochastic technique is used to determine the eddy–eddy coefficients, and a new least-squares regression method for the eddy–meanfield terms. Truncations are repeated for various T R , and the resolution dependence of the subgrid coefficients is identified. The mean jet structure and the kinetic and potential energy spectra resulting from the LESs closely agree with those from the benchmark simulations.

scholarly journals Nature versus Nurture in Shallow Convection

2010 ◽  
Vol 67 (5) ◽  
pp. 1655-1666 ◽  
Author(s):  
David M. Romps ◽  
Zhiming Kuang
Keyword(s):  
Standard Deviation ◽  
The Other ◽  
Cloud Base ◽  
Shallow Convection ◽  
Eddy Simulation ◽  
Cloud Properties ◽  
Nature Versus Nurture ◽  
Large Eddy ◽  
The Mean ◽  
Single Set

Abstract Tracers are used in a large-eddy simulation of shallow convection to show that stochastic entrainment (and not cloud-base properties) determines the fate of convecting parcels. The tracers are used to diagnose the correlations between a parcel’s state above the cloud base and both the parcel’s state at the cloud base and its entrainment history. The correlation with the cloud-base state goes to zero a few hundred meters above the cloud base. On the other hand, correlations between a parcel’s state and its net entrainment are large. Evidence is found that the entrainment events may be described as a stochastic Poisson process. A parcel model is constructed with stochastic entrainment that is able to replicate the mean and standard deviation of cloud properties. Turning off cloud-base variability has little effect on the results, which suggests that stochastic mass-flux models may be initialized with a single set of properties. The success of the stochastic parcel model suggests that it holds promise as the framework for a convective parameterization.

scholarly journals Prediction of flow and dispersion in cross–ventilated buildings

2019 ◽  
Vol 128 ◽  
pp. 05002
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Ali Nahavandi
Keyword(s):  
Computational Analysis ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Turbulence Structure ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Grid Independence

The present paper presents a detailed computational analysis of flow and dispersion in a generic isolated single–zone buildings. First, a grid generation strategy is discussed, that is inspired by a previous computational analysis and a grid independence study. Different turbulence models are appliedincluding two-equation turbulence models, the differential Reynolds Stress Model, Detached Eddy Simulation and Zonal Large Eddy Simulation. The mean velocity and concentration fields are calculated and compared with the measurements. A satisfactory agreement with the experiments is not observed by any of the modelling approaches, indicating the highly demanding flow and turbulence structure of the problem.

Study of wave effect on vorticity in Langmuir turbulence using wave-phase-resolved large-eddy simulation

2019 ◽  
Vol 875 ◽  
pp. 173-224 ◽  
Author(s):  
Anqing Xuan ◽  
Bing-Qing Deng ◽  
Lian Shen
Keyword(s):  
Large Eddy Simulation ◽  
Correlation Effect ◽  
Wave Turbulence ◽  
Langmuir Turbulence ◽  
Streamwise Vorticity ◽  
Wave Phase ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vorticity Dynamics ◽  
The Mean

The effects of a water surface wave on the vorticity in the turbulence underneath are studied for Langmuir turbulence using wave-phase-resolved large-eddy simulation. The simulations are performed on a dynamically evolving wave-surface-fitted grid such that the phase-resolved wave motions and their effects on the turbulence are explicitly captured. This study focuses on the vorticity structures and dynamics in Langmuir turbulence driven by a steady and co-aligned progressive wave and surface shear stress. For the first time, the detailed vorticity dynamics of the wave–turbulence interaction in Langmuir turbulence in a wave-phase-resolved frame is revealed. The wave-phase-resolved simulation provides detailed descriptions of many characteristic features of Langmuir turbulence, such as elongated quasi-streamwise vortices. The simulation also reveals the variation of the strength and the inclination angles of the vortices with the wave phase. The variation is found to be caused by the periodic stretching and tilting of the wave orbital straining motions. The cumulative effect of the wave on the wave-phase-averaged vorticity is analysed using the Lagrangian average. It is discovered that, in addition to the tilting effect induced by the Lagrangian mean shear gradient of the wave, the phase correlation between the vorticity fluctuations and the wave orbital straining is also important to the cumulative vorticity evolution. Both the fluctuation correlation effect and the mean tilting effect are found to amplify the streamwise vorticity. On the other hand, for the vertical vorticity, the fluctuation correlation effect cancels the mean tilting effect, and the net change of the vertical vorticity by the wave straining is negligible. As a result, the wave straining enhances only the streamwise vorticity and cumulatively tilts vertical vortices towards the streamwise direction. The above processes are further quantified analytically. The role of the fluctuation correlation effect in the wave-phase-averaged vorticity dynamics provides a deeper understanding of the physical processes underlying the wave–turbulence interaction in Langmuir turbulence.

scholarly journals On the Effects of Lateral Openings on Courtyard Ventilation and Pollution—A Large-Eddy Simulation Study

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 63 ◽  
Author(s):  
Tobias Gronemeier ◽  
Matthias Sühring
Keyword(s):  
Air Quality ◽  
Negative Impact ◽  
Flow Direction ◽  
Urban Environments ◽  
High Concentration ◽  
Eddy Simulation ◽  
Recreation Areas ◽  
Large Eddy ◽  
The Mean ◽  
Upstream Flow

Courtyards are an omnipresent feature within the urban environment. Residents often use courtyards as recreation areas, which makes them crucial for the physical and psychological comfort of the urban population. However, considering that courtyards represent enclosed cavities, they are often poorly ventilated spaces and pollutants from neighboring traffic, once entrained, can pose a serious threat to human health. Here, we studied the effects of lateral openings on courtyard pollution and ventilation. Therefore, we performed a set of large-eddy simulations for idealized urban environments with different courtyard configurations. While pollutant concentration and ventilation are barely modified by lateral openings for wide courtyards, lateral openings have a significant effect on the mean concentration, the number of high-concentration events and the ventilation within narrower and deeper courtyards. The impacts of lateral openings on air quality within courtyards strongly depend on their orientation with respect to the flow direction, as well as on the upstream flow conditions and upstream building configuration. We show that lateral openings, in most cases, have a negative impact on air quality; nevertheless, we also present configurations where lateral openings positively impact the air quality within courtyards. These outcomes may certainly contribute to improve future urban planning in terms of health protection.

scholarly journals Improving Estimates of the Antarctic Circumpolar Current Streamlines in Drake Passage

2008 ◽  
Vol 38 (5) ◽  
pp. 1000-1010 ◽  
Author(s):  
Yueng-Djern Lenn ◽  
Teresa K. Chereskin ◽  
Janet Sprintall
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Acoustic Doppler Current Profiler ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Dynamic Height ◽  
Current Profiler ◽  
Meridional Overturning ◽  
The Mean ◽  
Circumpolar Current

Abstract Accurately resolving the mean Antarctic Circumpolar Current (ACC) is essential for determining Southern Ocean eddy fluxes that are important to the global meridional overturning circulation. Previous estimates of the mean ACC have been limited by the paucity of Southern Ocean observations. A new estimate of the mean surface ACC in Drake Passage is presented that combines sea surface height anomalies measured by satellite altimetry with a recent dataset of repeat high-resolution acoustic Doppler current profiler observations. A mean streamfunction (surface height field), objectively mapped from the mean currents, is used to validate two recent dynamic height climatologies. The new streamfunction has narrower and stronger ACC fronts separated by quiescent zones of much weaker flow, thereby improving on the resolution of ACC fronts observed in the other climatologies. Distinct streamlines can be associated with particular ACC fronts and tracked in time-dependent maps of dynamic height. This analysis shows that varying degrees of topographic control are evident in the preferred paths of the ACC fronts through Drake Passage.

Large Eddy Simulation of Round Impinging Jets With Large Stand-Off Distance

2014 ◽  
Author(s):  
Mehrdad Shademan ◽  
Vesselina Roussinova ◽  
Ron Barron ◽  
Ram Balachandar
Keyword(s):  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Vortical Structures ◽  
Nozzle Height ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Good Agreement

Large Eddy Simulation (LES) has been carried out to study the flow of a turbulent impinging jet with large nozzle height-to-diameter ratio. The dynamic Smagorinsky model was used to simulate the subgrid-scale stresses. The jet exit Reynolds number is 28,000. The study presents a detailed evaluation of the flow characteristics of an impinging jet with nozzle height of 20 diameters above the plate. Results of the mean normalized centerline velocity and wall shear stress show good agreement with previous experiments. Analysis of the flow field shows that vortical structures generated due to the Kelvin-Helmholtz instabilities in the shear flow close to the nozzle undergo break down or merging when moving towards the plate. Unlike impinging jets with small stand-off distance where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for this large stand-off distance. A large deflection of the jet axis was observed for this type of impinging jet when compared to the cases with small nozzle height-to-diameter ratios.

Jets of the Antarctic Circumpolar Current in the Drake Passage Based on Hydrographic Section Data

2020 ◽  
Author(s):  
Roman Tarakanov ◽  
Alexander Gritsenko
Keyword(s):  
Antarctic Circumpolar Current ◽  
Basic Research ◽  
Drake Passage ◽  
Section Data ◽  
Temporal And Spatial ◽  
Circumpolar Current ◽  
Basic Research Grant ◽  
The Antarctic ◽  
Jet Structure ◽  
Satellite Altimetry Data

&lt;p&gt;We have analyzed the fine structure of Antarctic Circumpolar Current jets in the Drake Passage based on CTD and SADCP measurements over two hydrographic sections in January 2010 and October&amp;#8211;November 2011. Eleven jets with a local horizontal velocity maximum were revealed in 2010, and nine jets were in 2011. These individual jets were various combinations of 12 jets of the Antarctic Circumpolar Current, which we revealed earlier in the region south of Africa on the basis of the section data in December 2009. Daily satellite altimetry data available at http://www.aviso.altimetry.fr were also used to interpret the synoptic patterns of currents over the sections. These results allow us to suggest that the multi-jet structure with a number of jets exceeding nine reported by Sokolov&amp;Rintoul, 2009 is common for the entire circumpolar circle and even for regions with significant contraction of the ACC, such as the Drake Passage. However, the question about the number of jets and its temporal and spatial permanency remains open. Investigation was supported by Russian Foundation of Basic Research grant No 18-05-00283.&lt;/p&gt;

LARGE EDDY SIMULATION OF THE PHENOMENOLOGY OF THE FLOW THROUGH A LINEAR BLADE CASCADE – THE MEAN FIELD

2017 ◽  
Vol 20 (1) ◽  
pp. 1-20
Author(s):  
Karima Heguehoug ép. Benkara-Mostefa ◽  
Zoubir Nemouchi ◽  
Lahouari Adjlout
Keyword(s):  
Large Eddy Simulation ◽  
Mean Field ◽  
Eddy Simulation ◽  
Blade Cascade ◽  
Large Eddy ◽  
Flow Through ◽  
The Mean

Numerical Investigation of Turbulent Flow in a T-Junction

2011 ◽  
Author(s):  
Jungwoo Kim ◽  
Jae Jun Jeong
Keyword(s):  
Thermal Fatigue ◽  
Turbulent Mixing ◽  
Azimuthal Angle ◽  
Dominant Frequency ◽  
Frequency Characteristics ◽  
Turbulent Pipe Flow ◽  
Energy Spectra ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

In the present study, a large eddy simulation, at conditions of experiments by Vattenfall, was performed in order to investigate the phenomenon of turbulent mixing affecting the thermal fatigue in a T-junction. Mean velocity and turbulence intensity from the simulation are compared against those measured in the Vattenfall experiment, and the observed agreement is good. Based on the numerical results from the LES, the energy spectra were examined because they have been regarded as being of primary importance in the study on the thermal fatigue according to previous studies. The energy spectra showed the dominant frequency of around St = 0.5 agrees with the value reported in experiments. Also, near the T-junction the frequency characteristics are shown to depend on the azimuthal angle. However, this dependency of the frequency characteristics on the azimuthal angle is disappeared in downstream because the turbulence in the T-junction eventually approaches the fully-developed turbulent pipe flow. On the other hand, although not shown here, the dominant frequency near the wall is different from that reported at the centerline (St∼1), meaning that the thermal fatigue may not result from the wake structure, and is affected by the vertical structures existing near the wall. This result is consistent with one stated by [1] that the frequency characteristics are closely associated with arched vortices.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

2011 ◽  
Vol 383-390 ◽  
pp. 5344-5349
Author(s):  
Zhen Bu
Keyword(s):  
Natural Ventilation ◽  
Ventilation Rate ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Ventilation ◽  
The Mean ◽  
Ventilation Rates ◽  
Les Model ◽  
Good Agreement

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

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