Large-eddy simulations of turbulent mixing layers using the stretched-vortex model

2011 ◽  
Vol 671 ◽  
pp. 507-534 ◽  
Author(s):  
T. W. MATTNER
Keyword(s):  
Large Scale ◽  
Large Eddy Simulations ◽  
Mixing Layers ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Subgrid Model ◽  
Large Eddy ◽  
Schmidt Numbers ◽  
Self Similar ◽  
Large Scale Flow

The stretched-vortex subgrid model is used to run large-eddy simulations of temporal mixing layers at various Reynolds and Schmidt numbers, with different initial and boundary conditions. A self-similar flow is obtained, during which the growth rate, mean velocity and Reynolds stresses are in accord with experimental results. However, predictions of the amount of mixed fluid, and of the variation in its composition across the layer, are excessive, especially at high Schmidt number. More favourable comparisons between experiment and simulation are obtained when the large-scale flow is quasi-two-dimensional; however, such states are not self-similar and not sustainable. Present model assumptions lead to predictions of the continued subgrid spectrum with a viscous cutoff that is dependent on grid resolution.

Stochastic backscatter in large-eddy simulations of boundary layers

1992 ◽  
Vol 242 ◽  
pp. 51-78 ◽  
Author(s):  
P. J. Mason ◽  
D. J. Thomson
Keyword(s):  
Large Scale ◽  
Flow Simulation ◽  
Surface Region ◽  
Large Eddy Simulations ◽  
Flow Profile ◽  
Mean Velocity ◽  
Near Surface ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy

The ability of a large-eddy simulation to represent the large-scale motions in the interior of a turbulent flow is well established. However, concerns remain for the behaviour close to rigid surfaces where, with the exception of low-Reynolds-number flows, the large-eddy description must be matched to some description of the flow in which all except the larger-scale ‘inactive’ motions are averaged. The performance of large-eddy simulations in this near-surface region is investigated and it is pointed out that in previous simulations the mean velocity profile in the matching region has not had a logarithmic form. A number of new simulations are conducted with the Smagorinsky (1963) subgrid model. These also show departures from the logarithmic profile and suggest that it may not be possible to eliminate the error by adjustments of the subgrid lengthscale. An obvious defect of the Smagorinsky model is its failure to represent stochastic subgrid stress variations. It is shown that inclusion of these variations leads to a marked improvement in the near-wall flow simulation. The constant of proportionality between the magnitude of the fluctuations in stress and the Smagorinsky stresses has been empirically determined to give an accurate logarithmic flow profile. This value provides an energy backscatter rate slightly larger than the dissipation rate and equal to idealized theoretical predictions (Chasnov 1991).

High-Cycle Thermal Fatigue in Mixing Tees: New Large-Eddy Simulations Validated Against New Data Obtained by PIV in the Vattenfall Experiment

2009 ◽  
Author(s):  
Ylva Odemark ◽  
Torbjo¨rn M. Green ◽  
Kristian Angele ◽  
Johan Westin ◽  
Farid Alavyoon ◽  
...  
Keyword(s):  
Large Scale ◽  
High Amplitude ◽  
Large Eddy Simulations ◽  
Turbulence Statistics ◽  
Mean Velocity ◽  
Time Resolved ◽  
Large Scale Structures ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Component Particle

New data was obtained for a previously studied T-junction experimental setup [1] for a range of flow ratios between hot and cold flows in order to validate new Large Eddy Simulations (LES). The instantaneous velocity field downstream of the T-junction was measured with two-component Particle Image Velocimetry (PIV) in several horizontal and vertical planes at the centre line downstream of the T-junction. The generated PIV database enables a thorough validation of CFD turbulence statistics. The turbulence statistics are shown to be well predicted despite the fact that the mesh in the LES is rather coarse. By usage of time resolved PIV the temporal evolution of the predominant low frequent large-scale structures, responsible for much of the mixing and the high amplitude temperature fluctuations on the walls, were captured. Those structures are, however, weaker in LES than in PIV, being in line with the fact that the wake region behind the penetrating vertical hot jet is underpredicted in LES. Tests regarding the influence of the LES-results to the shape of the inlet boundary conditions (developed or flat symmetric mean-velocity profiles) were carried out and the sensitivity in the results was shown to be small. Furthermore, the results show good agreement with the experimental data independent of the flow ratio between the hot and the cold flows.

Compression of a Swirling and Tumbling Flow

2013 ◽  
Author(s):  
Martin Söder ◽  
Lisa Prahl Wittberg ◽  
Björn Lindgren ◽  
Laszlo Fuchs
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Structures ◽  
Large Eddy ◽  
Tumbling Motion ◽  
Large Scale Flow

The effect of compression on a swirling/tumbling flow is studied using Large-Eddy Simulations (LES). In this study the geometry investigated is a cylinder with an artificially created swirling/tumbling motion. During compression the evolution of turbulence and vorticity are investigated. An increase of turbulence and vorticity is observed and linked to vorticity-dilatation interaction. It is shown that for swirling/tumbling flows turbulent kinetic energy available at Top Dead Center (TDC) is introduced by the piston through the vorticity-dilatation interaction and that turbulence increases independently of the presence of instability of the large scale flow structures.

scholarly journals Subgrid Model with Scaling Laws for Atmospheric Simulations

2012 ◽  
Vol 69 (4) ◽  
pp. 1427-1445 ◽  
Author(s):  
Vassili Kitsios ◽  
Jorgen S. Frederiksen ◽  
Meelis J. Zidikheri
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Scaling Laws ◽  
Subgrid Scale ◽  
Flow Strength ◽  
Atmospheric Flows ◽  
Subgrid Model ◽  
Large Eddy ◽  
Self Similar

Abstract Subgrid-scale parameterizations with self-similar scaling laws are developed for large-eddy simulations (LESs) of atmospheric flows. The key new contribution is the development of scaling laws that govern how these parameterizations depend on the LES resolution and flow strength. Both stochastic and deterministic representations of the effects of subgrid-scale eddies on the retained scales are considered. The stochastic subgrid model consists of a backscatter noise term and a drain eddy viscosity, while in the deterministic subgrid model the net effect of these two terms is represented by a net eddy viscosity. In both cases the subgrid transfers are calculated self-consistently from the statistics of higher-resolution-reference direct numerical simulations (DNSs). The dependence of the subgrid parameterizations on the resolution of the LESs is determined for DNSs having resolutions up to triangular 504 wavenumber truncations. The subgrid parameterizations are developed for typical large-scale atmospheric flows and for different strengths and spectra of kinetic energy within a quasigeostrophic spectral model. LESs using the stochastic and deterministic subgrid parameterizations are shown to replicate the kinetic energy spectra of the reference DNS at the scales of the LESs. It is found that the maximum strengths of the drain, net, and backscatter viscosities satisfy scaling laws dependent on the LES truncation wavenumber and that the dependence of these eddy viscosities on total wavenumber can also be written as essentially universal functions that depend on flow strength and resolution. The scaling laws make the subgrid-scale parameterizations more generally applicable in LESs and remove the need to generate them from reference DNSs.

Large eddy simulations of variable property turbulent flow in horizontal and vertical channels with buoyancy and heat transfer effects

2007 ◽  
Vol 221 (4) ◽  
pp. 429-441 ◽  
Author(s):  
J S Lee ◽  
R H Pletcher
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Vertical Channel ◽  
Large Eddy Simulations ◽  
Mean Flow ◽  
Mean Velocity ◽  
Velocity Fluctuations ◽  
Combined Flow ◽  
Large Eddy ◽  
The Mean

Turbulent combined flow of forced and natural convection was investigated using large eddy simulations for horizontal and vertical channels with significant heat transfer. The walls were maintained at constant temperatures, one heated and the other cooled, at temperature ratios of 1.01, 1.99, and 3.00, respectively. Results showed that with increasing the Grashof number, large-scale turbulent motions emerged near the wall, resulting in significant changes in turbulent intensities for the horizontal channel flow case. Aiding and opposing flows, however, for the vertical channel, emerge near the heated and cooled walls, respectively, while the pressure gradient drives the mean flow upwards. Buoyancy effects on the mean velocity, temperature, and turbulent intensities were observed near the walls. In the aiding flow, the turbulent intensities and heat transfer were suppressed and the flow was relaminarized at large values of the Grash of number. In the opposing flow, however, turbulence was enhanced with increasing velocity fluctuations.

scholarly journals Linear-eddy subgrid model for reacting large-eddy simulations - Heat release effects

1997 ◽  
Author(s):  
William Calhoon, Jr. ◽  
Suresh Menon ◽  
William Calhoon, Jr. ◽  
Suresh Menon
Keyword(s):  
Heat Release ◽  
Large Eddy Simulations ◽  
Subgrid Model ◽  
Large Eddy

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>

scholarly journals High-resolution large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere

2013 ◽  
Vol 13 (12) ◽  
pp. 31891-31932 ◽  
Author(s):  
R. Paoli ◽  
O. Thouron ◽  
J. Escobar ◽  
J. Picot ◽  
D. Cariolle
Keyword(s):  
Large Scale ◽  
Lower Stratosphere ◽  
Atmospheric Model ◽  
Large Eddy Simulations ◽  
Stratified Flows ◽  
Flow Topology ◽  
Upper Troposphere ◽  
Large Eddy ◽  
Scale Turbulence ◽  
The Impact

Abstract. Large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere (UTLS) are carried out and analyzed using the mesoscale atmospheric model Méso-NH. Different levels of turbulence are generated using a large-scale stochastic forcing technique that was especially devised to treat atmospheric stratified flows. The study focuses on the analysis of turbulence statistics, including mean quantities and energy spectra, as well as on a detailed description of flow topology. The impact of resolution is also discussed by decreasing the grid spacing to 2 m and increasing the number of grid points to 8×109. Because of atmospheric stratification, turbulence is substantially anisotropic, and large elongated structures form in the horizontal directions, in accordance with theoretical analysis and spectral direct numerical simulations of stably stratified flows. It is also found that the inertial range of horizontal kinetic energy spectrum, generally observed at scales larger than a few kilometers, is prolonged into the sub-kilometric range, down to the Ozmidov scales that obey isotropic Kolmorogov turbulence. The results are in line with observational analysis based on in situ measurements from existing campaigns.

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