An Advanced Mixing Tee Mock-Up Called “The Skin of the Fluid” Designed to Qualify the Numerical LES Analyses Applied to the Thermal Evaluation

2006 ◽  
Author(s):  
Olivier Braillard ◽  
Olivier Berder ◽  
Fre´de´ric Escourbiac ◽  
Slim Constans
Keyword(s):  
Infrared Image ◽  
Simulation Models ◽  
Temperature Fluctuations ◽  
Comparative Approach ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Local Measurements ◽  
Fluctuation Temperature ◽  
Time Observation

Nowadays, the LES (Large Eddy Simulation) models have reached an advanced stage in the thermal hydraulic numerical analyses. Particularly, in the mixing tee geometry, the LES allows the thermal, temperature fluctuations cartography — both in amplitude and frequency — to be evaluated. However, for the purpose of mechanical studies a better determination of the fluctuation temperature which impacts the wall would be of significant interest, magnitude of the fluctuation being directly linked to the lifetime of the Tee. This demand steps of experimental qualifications based on cartographic comparisons between numerical and experimental results, not compatible with basic current experiments proposing only local measurements. A mixing tee mock-up (␀ 50 mm) called “the skin of the fluid” was designed to show the real time observation of the temperature fluctuations in the mixing area with a digital infrared device. With its low Biot number the mock-up is quasi permeable to the fluctuation and does not attenuate the temperature amplitude at high frequency, consequently, the infrared image represents the temperature fluctuations which impacts the wall. An existent LES numerical analysis performed with the TRIO U code (developed by the CEA) on the same geometry is shown for a first comparative approach.

scholarly journals Supersaturation calculation in large eddy simulation models for prediction of the droplet number concentration

2012 ◽  
Vol 5 (3) ◽  
pp. 761-772 ◽  
Author(s):  
O. Thouron ◽  
J.-L. Brenguier ◽  
F. Burnet
Keyword(s):  
Cloud Condensation Nuclei ◽  
Simulation Models ◽  
Number Concentration ◽  
Eddy Simulation ◽  
Droplet Concentration ◽  
Large Eddy ◽  
Condensed Water ◽  
Les Model ◽  
Adjustment Scheme ◽  
Cloud Core

Abstract. A new parameterization scheme is described for calculation of supersaturation in LES models that specifically aims at the simulation of cloud condensation nuclei (CCN) activation and prediction of the droplet number concentration. The scheme is tested against current parameterizations in the framework of the Meso-NH LES model. It is shown that the saturation adjustment scheme, based on parameterizations of CCN activation in a convective updraft, overestimates the droplet concentration in the cloud core, while it cannot simulate cloud top supersaturation production due to mixing between cloudy and clear air. A supersaturation diagnostic scheme mitigates these artefacts by accounting for the presence of already condensed water in the cloud core, but it is too sensitive to supersaturation fluctuations at cloud top and produces spurious CCN activation during cloud top mixing. The proposed pseudo-prognostic scheme shows performance similar to the diagnostic one in the cloud core but significantly mitigates CCN activation at cloud top.

scholarly journals Assessment of Grid Anisotropy Effects on Large-Eddy-Simulation Models with Different Length Scales

AIAA Journal ◽  
2020 ◽  
Vol 58 (10) ◽  
pp. 4522-4533
Author(s):  
Jan-Erik Schumann ◽  
Siavash Toosi ◽  
Johan Larsson
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Models ◽  
Length Scales ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Grid Anisotropy

Large-eddy simulation of turbulent flow over a two-dimensional cavity with temperature fluctuations

1999 ◽  
Vol 42 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Arlindo de Matos ◽  
Francisco A.A. Pinho ◽  
Aristeu Silveira-Neto
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Temperature Fluctuations ◽  
Two Dimensional ◽  
Eddy Simulation ◽  
Large Eddy

Large Eddy Simulation of Turbulent Heat Transfer in Curved-Pipe Flow

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Pipe Flow ◽  
Temperature Fluctuations ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Subgrid Scale ◽  
Curved Pipe ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean

In the present investigation, turbulent heat transfer in fully developed curved-pipe flow has been studied by using large eddy simulation (LES). We consider a fully developed turbulent curved-pipe flow with axially uniform wall heat flux. The friction Reynolds number under consideration is Reτ  = 1000 based on the mean friction velocity and the pipe radius, and the Prandtl number (Pr) is 0.71. To investigate the effects of wall curvature on turbulent flow and heat transfer, we varied the nondimensionalized curvature (δ) from 0.01 to 0.1. Dynamic subgrid-scale models for turbulent subgrid-scale stresses and heat fluxes were employed to close the governing equations. To elucidate the secondary flow structures due to the pipe curvature and their effect on the heat transfer, the mean quantities and various turbulence statistics of the flow and temperature fields are presented, and compared with those of the straight-pipe flow. The friction factor and the mean Nusselt number computed in the present study are in good agreement with the experimental results currently available in the literature. We also present turbulence intensities, skewness and flatness factors of temperature fluctuations, and cross-correlations of velocity and temperature fluctuations. In addition, we report the results of an octant analysis to clarify the correlation between near-wall turbulence structures and temperature fluctuation in the vicinity of the pipe wall. Based on our results, we attempt to clarify the effects of the pipe curvature on turbulent heat transfer. Our LES provides researchers and engineers with useful data to understand the heat-transfer mechanisms in turbulent curved-pipe flow, which has numerous applications in engineering.

Hybrid Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation Models for Flow Around an Iced Wing

2015 ◽  
Vol 52 (1) ◽  
pp. 244-256 ◽  
Author(s):  
M. F. Alam ◽  
David S. Thompson ◽  
D. Keith Walters
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Models ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Evaluation of the WRF PBL Parameterizations for Marine Boundary Layer Clouds: Cumulus and Stratocumulus

2013 ◽  
Vol 141 (7) ◽  
pp. 2265-2271 ◽  
Author(s):  
Hsin-Yuan Huang ◽  
Alex Hall ◽  
Joao Teixeira
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Layer Structure ◽  
Model Performance ◽  
Simulation Models ◽  
Eddy Diffusivity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Boundary Layer Cloud

Abstract The performance of five boundary layer parameterizations in the Weather Research and Forecasting Model is examined for marine boundary layer cloud regions running in single-column mode. Most parameterizations show a poor agreement of the vertical boundary layer structure when compared with large-eddy simulation models. These comparisons against large-eddy simulation show that a parameterization based on the eddy-diffusivity/mass-flux approach provides a better performance. The results also illustrate the key role of boundary layer parameterizations in model performance.

scholarly journals DNS and LES of the Compressible Flow Over a Delta Wing With the Symmetry-Preserving Discretization

2014 ◽  
Author(s):  
Wybe Rozema ◽  
Johan C. Kok ◽  
Roel W. C. P. Verstappen ◽  
Arthur E. P. Veldman
Keyword(s):  
Compressible Flow ◽  
Delta Wing ◽  
Region Of Interest ◽  
Simulation Models ◽  
Simulation Method ◽  
Discrete Level ◽  
Artificial Dissipation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Stability

A fourth-order accurate symmetry-preserving discretization for compressible flow is used to perform simulations of the turbulent flow over a delta wing. A symmetry-preserving discretization eliminates the non-linear convective instability by preserving conservation of kinetic energy at the discrete level. This enhances the stability of a simulation method, so that little artificial dissipation is needed for numerical stability. It is shown that simulations of the flow over a sharp-edge delta wing at Re = 50,000 with the symmetry-preserving discretization are stable without artificial dissipation in a region of interest around the delta wing. To assess the accuracy of the simulation method, results obtained on a fine computational grid are compared with results obtained on a coarser grid. Also results obtained with large-eddy simulation models and with sixth-order artificial dissipation are presented.

scholarly journals The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

2015 ◽  
Vol 8 (4) ◽  
pp. 3481-3522 ◽  
Author(s):  
P. J. H. Volker ◽  
J. Badger ◽  
A. N. Hahmann ◽  
S. Ott
Keyword(s):  
Large Scale ◽  
Wind Farm ◽  
Mesoscale Model ◽  
Wind Farms ◽  
Simulation Models ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. We describe the theoretical basis, implementation and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP), uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

scholarly journals Control of a Lifted H2/N2 Flame by Axial and Flapping Forcing: A Numerical Study

2021 ◽  
Author(s):  
Artur Tyliszczak ◽  
Agnieszka Wawrzak
Keyword(s):  
Numerical Study ◽  
Temperature Fluctuations ◽  
Mixing Process ◽  
Stochastic Field ◽  
Field Approach ◽  
Eddy Simulation ◽  
Fuel Jet ◽  
Large Eddy ◽  
Lift Off ◽  
The Impact

Abstract The large eddy simulation (LES) method combined with the Eulerian stochastic field approach has been used to study excited lifted hydrogen flames in a stream of hot co-flow air in a configuration closely corresponding to the so-called Cabra flame. The excitation is obtained by adding to an inlet velocity profile three types of forcing ((i) axial; (ii) flapping; (iii) combination of both) with amplitude of 15% of the fuel jet velocity and frequency corresponding to the Strouhal numbers St=0.30, 0.45, 0.60 and 0.75. It is shown that such a type of forcing significantly changes the lift-off height Lh of the flame and its global shape, resulting in a flame occupying large volume or the flame, which downstream the nozzle transforms from the circular one into a quasi-planar flame. Both the Lh and their spreading angles of the flames were found to be a function of the type of the forcing and its frequency. The minimum value of Lh has been found for the case with the combination of axial and flapping forcing at the frequency close to the preferred one in the unexcited configuration. The impact of the flapping forcing manifested through a widening of the flame in the flapping direction. It was shown that the excitation can significantly increase the level of the velocity and temperature fluctuations intensifying the mixing process. The computational results are validated based on the solutions obtained for a non-excited flame for which experimental data are available.

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