Computational Studies of Two-Dimensional Rayleigh-Taylor Driven Mixing for a Tilted-Rig

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Malcolm J. Andrews ◽  
David L. Youngs ◽  
Daniel Livescu ◽  
Tie Wei
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Two Dimensional ◽  
Complex Flows ◽  
Molecular Mixing ◽  
One Dimensional ◽  
Large Eddy ◽  
Mixing Problem ◽  
Good Agreement

A time-dependent, incompressible, turbulent mixing problem, referred here to as the “tilted-rig,” is defined, based results from an experiment that involved the introduction of a large-scale overturning motion, with a superposed localized Rayleigh-Taylor (RT) driven mixing. The problem serves to examine the development of RT turbulent mixing while being strained by a large-scale two-dimensional confined motion. Care is taken to define the problem in detail so others might use the definition, and the results, to help develop advanced models of buoyancy driven mixing in complex flows. Aside from a careful definition, the problem has been solved using two different implicit-large-Eddy-simulations (ILES) based codes, and with a direct numerical simulations (DNS) code. Two-dimensional and one-dimensional mix metrics are defined, and then used to examine the development of the mixing region, and the overall evolution of the flow. Comparison of simulations with experiment reveals that large-scale overturning can be well captured in all the simulations, similarly central mix widths, and spike/bubble sidewall penetrations are also in good agreement. A comparison between the different simulation methodologies, ILES and DNS, reveals an overall good agreement between mix metrics such as the amount of molecular mixing. The DNS simulations reveal a dependency on Reynolds number that merits further experimental work.

A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model

2018 ◽  
Vol 28 (10) ◽  
pp. 2463-2479 ◽  
Author(s):  
Salman Arshad ◽  
Bo Kong ◽  
Alan Kerstein ◽  
Michael Oevermann
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Passive Scalar ◽  
Mixing Model ◽  
Large Eddy Simulations ◽  
High Flux ◽  
Scalar Mixing ◽  
Content Type ◽  
Large Eddy

PurposeThe purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM.Design/methodology/approachThe new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done.FindingsThe simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined.Originality/valueThe splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids.

scholarly journals Two-Dimensional Spectra in the Atmospheric Boundary Layer

2006 ◽  
Vol 63 (11) ◽  
pp. 3066-3070 ◽  
Author(s):  
Mark Kelly ◽  
John C. Wyngaard
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Field Measurements ◽  
Large Eddy Simulations ◽  
Two Dimensional ◽  
One Dimensional ◽  
Meteorological Field ◽  
Large Eddy ◽  
Using Data ◽  
Reliable Scale

Abstract One-dimensional spectra are frequently used to relate features of measured and simulated meteorological field variables in the turbulent atmospheric boundary layer (ABL), but two-dimensional spectra can provide more reliable scale information than one-dimensional spectra. Here a method is presented for obtaining two-dimensional spectra from one-dimensional spectra, and it includes examples using data from large-eddy simulations and field measurements in the ABL.

Near Wall Resolution Requirements for High-Order FR/CPR Method for Wall-Resolved Large Eddy Simulations

2020 ◽  
Author(s):  
Rathakrishnan Bhaskaran ◽  
Gustavo Ledezma
Keyword(s):  
High Order ◽  
Large Eddy Simulations ◽  
Grid Resolution ◽  
Wall Turbulence ◽  
Two Dimensional ◽  
Data Set ◽  
Large Eddy ◽  
Mixing Problem ◽  
Resolution Requirements ◽  
Near Wall

Abstract This study aims to establish near wall resolution requirements for wall-resolved Large Eddy Simulations (LES) using the Flux Reconstruction / Correction Procedure via Reconstruction (FR/CPR) method. The FR/CPR method is relatively new and its numerical capabilities for LES are not well established. A high-order unstructured LES solver (GENESIS) based on the FR/CPR approach is used to study two canonical near wall turbulent flow problems. The first problem concerns spatial development of a turbulent flat plate boundary layer. The grid resolution requirement for various polynomial orders is established and the skin-friction and near wall turbulence is compared to theory and Direct Numerical Simulation (DNS) results. The second problem studied is the two-dimensional wall film case of Kacker and Whitelaw (1968, 1969). This is a thermal mixing problem consisting of a two-dimensional jet for various mass flow ratios and plate thicknesses. This study focuses on one of the cases from this data set, corresponding to a thick plate. Well resolved LES simulations show an excellent agreement with measured adiabatic film effectiveness. The effect of polynomial order and grid resolution is investigated and near wall resolution requirements are established.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

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 Stability and Sensitivity Analysis of Hydrodynamic Instabilities in Industrial Swirled Injection Systems

2017 ◽  
Author(s):  
Thomas L. Kaiser ◽  
Thierry Poinsot ◽  
Kilian Oberleithner
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Vortex Core ◽  
Large Eddy Simulations ◽  
Mode Shapes ◽  
Mean Flow ◽  
Precessing Vortex Core ◽  
Large Eddy ◽  
Good Agreement

The hydrodynamic instability in an industrial, two-staged, counter-rotative, swirled injector of highly complex geometry is under investigation. Large eddy simulations show that the complicated and strongly nonparallel flow field in the injector is superimposed by a strong precessing vortex core. Mean flow fields of large eddy simulations, validated by experimental particle image velocimetry measurements are used as input for both local and global linear stability analysis. It is shown that the origin of the instability is located at the exit plane of the primary injector. Mode shapes of both global and local linear stability analysis are compared to a dynamic mode decomposition based on large eddy simulation snapshots, showing good agreement. The estimated frequencies for the instability are in good agreement with both the experiment and the simulation. Furthermore, the adjoint mode shapes retrieved by the global approach are used to find the best location for periodic forcing in order to control the precessing vortex core.

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