@unpublished {374,
title = {Large scale in transit computation of quantiles for ensemble runs},
year = {2019},
keywords = {In Situ Data Processing, Iterative Statistics, Parametric Studies, Robbins-Monro, Uncertainty Quantification},
url = {https://hal.inria.fr/hal-02016828},
author = {Ribes, Alejandro and Terraz, Th{\'e}ophile and Iooss, Bertrand and Fournier, Yvan and Raffin, Bruno}
}
@article {377,
title = {Low-order reconstruction operators on polyhedral meshes: application to compatible discrete operator schemes},
journal = {Computer Aided Geometric Design},
volume = {35-36},
year = {2015},
pages = {27 - 41},
doi = {https://doi.org/10.1016/j.cagd.2015.03.015},
author = {J. Bonelle and D. A. Di Pietro and A. Ern}
}
@article {291,
title = {Large Eddy Simulation and the effect of the turbulent inlet conditions in the mixing Tee},
journal = {Nuclear Engineering and Design},
volume = {241},
year = {2011},
pages = {2178-2183},
abstract = {Thermal fatigue in Pressurized Water Reactor plants has been found to be very acute in some hot/cold Tee junction mixing zones. Large Eddy Simulation (LES) can be used to capture the unsteadiness which is responsible for the large mechanical stresses associated with thermal fatigue. Here one LES subgrid model is studied, namely the Dynamic Smagorinsky model. This paper has two goals. The first is to demonstrate some results obtained using the EDF R\&D Code Saturne applied to the Vattenfall Tee junction benchmark (version 2006) and the second is to look at the effect of including synthetic turbulence at the Tee junction pipe inlets. The last goal is the main topic of this paper. The Synthetic Eddy Method is used to create the turbulent inlet conditions and is applied to two kinds of grids. One contains six million cells and the other ten million. The addition of turbulence at the inlet does not seem to have much effect on the bulk flow and all computations are in good agreement with the experimental data. However, the inlet turbulence does have an effect on the near wall flow. All cases show that the wall temperature fluctuation and the wall temperature/velocity correlation are not the same when a turbulent inlet condition is used. Inclusion of the turbulent inlet condition moves the downstream location of the maximum temperature/velocity correlation by 1 cm and reduces its magnitude by 10\%. This result is very important because the temperature/velocity correlation is closely related to the turbulent heat transfer in the flow, which is in turn responsible for the mechanical stresses on the structure. Finally we have studied in detail the influence of the turbulent inlet condition just downstream of the mixing zone. We show the influence of including turbulent inlet condition on the structure of the flow Walker et al. (2009).},
url = {http://www.sciencedirect.com/science/article/pii/S0029549311001907},
author = {Jean-Marc Ndombo and Richard J.A. Howard}
}
@article {108,
title = {Large eddy simulation of the flow around single and two side-by-side cylinders at subcritical Reynolds numbers},
journal = {Phys. Fluids},
volume = {23},
year = {2011},
publisher = {American Institute of Physics},
abstract = {The flow around single and two side-by-side infinite cylinders is numerically modelled using dynamic Smagorinsky large eddy simulation (LES). For the single cylinder, the Reynolds number based on the diameter and the free stream velocity is 3900. A complete sensitivity study was conducted based on the extrusion length in the span-wise direction, the grid refinement at the wall, the convection scheme, and the sub-grid scale (SGS) model. It was found that the mean solution is not influenced by the extrusion length beyond 4 diameters or by 1\% up-winding. However, coarsening the mesh in the wall normal direction or switching off the sub-grid scale model led to drastic effects on the recirculation length and on the underlying velocity field. The two side-by-side cylinders were tested for a range of pitch to diameter ratios (T/D = 1.0,1.25 <= T/D <= 5.0) at a Reynolds number of 3000. For the intermediate pitch to diameter ratios (1.25 <= T/D <= 1.75), multiple shedding frequencies were detected with a biased wake flow deflection. Furthermore, this biased flow deflection was found to be bistable, i.e., it changes the direction (flipping over) intermittently from one side to the other. This behavior was found to be consistent with reported experimental measurements. During the flip-over from one stable mode to the other, the intermittent gap vortex shedding was found to be stronger than for a stable mode, with in-phase vortex shedding. However, for the higher pitch ratio cases (T/D >= 2), a symmetrical wake behavior with anti-phase vortex shedding was observed.},
keywords = {convection, external flows, flow instability, flow simulation, numerical analysis, turbulence, vortices, wakes},
issn = {1070-6631},
doi = {http://link.aip.org/link/doi/10.1063/1.3596267},
url = {http://pof.aip.org/resource/1/phfle6/v23/i7/p075101_s1?isAuthorized=no},
author = {I. Afgan and Y. Kahil and S. Benhamadouche and P. Sagaut}
}
@mastersthesis {79,
title = {LES and Hybrid RANS/LES turbulence modelling in unstructured finite volume code and applications to nuclear reactor fuel bundle},
volume = {PhD Thesis,The University of Manchester},
year = {2010},
month = {10/2010},
school = {The University of Manchester},
type = {traditional},
abstract = {Rod bundle is a typical constitutive element of a very wide range of nuclear reactor designs. This thesis describes the investigation of such geometry with wall-resolved Large Eddy Simulation (LES). In order to alleviate the mesh constraint, imposed by the near wall resolution, the usage of embedded refinements and polyhedral meshes is analysed firstly with a inviscid laminar case (Taylor Green vortices) and secondly with a fully turbulent case (channel flow only with embedded refinement). The inviscid test case shows that the addition of embedded refinements decreases the conservation properties of the code. Indeed the accuracy decreases from second order in a structured conformal mesh, to something in between first and second order depending on the quality of the unstructured mesh. Better results are obtained when the interface between refined and coarse areas presents a more regular and structured pattern, reducing the generation of skewed and stretched cells. The channel flow simulation shows that the Reynolds stresses, of some embedded refined meshes, are affected by spurious oscillations. Surprisingly this effect is present in the unstructured meshes with the best orthogonal properties. Indeed analysis of Reynolds stress budgets shows that terms, where the gradient in the wall normal direction is dominant, have a largely oscillatory behaviour. The cause of the problem is attributed to the convective term and in particular in the method used for the gradient reconstruction. As a consequence of these contradictory signs between the inviscid and the fully turbulent cases, the rod bundle test case is analysed using a conventional body fitted multiblock mesh. Two different Reynolds numbers are investigated reporting Reynolds stresses and budgets. The flow is characterised by an energetic and almost periodic azimuthal flow pulsation in the gap region between adjacent sub-channels, which makes turbulent quantities largely different from those in plane channel and pipes and enhances mixing. Experiments found that a constant Strouhal number, with the variation of the Reynolds number, characterises the phenomenon. The frequency analysis finds that present simulations are distinguished by three dominant frequencies, the first in agreement with the experimental value and two higher ones, which might be due to the correlation of the azimuthal velocity in the streamwise direction. Several passive temperature fields are added at the simulations in order to study the effects of the variation of the Prandtl number and the change in boundary conditions (Neumann and Dirichlet). A simplified case where an imbalance of the scalar between adjacent sub-channels is also investigated in order to evaluate the variation of the heat fluxes with respect to the homogeneous case. An alternative solution, to reduce the mesh constraint imposed by the wall, is to hybridize LES with RANS. The main achievement of this work is to integrate the heat transfer modelling to the already existing model for the dynamic part. Further investigations of the blending function, used to merge the two velocity fields, are carried out in conjunction with a study of the model dependency on the mesh resolution. The validation is performed on a fully developed channel flow at different Reynolds numbers and with constant wall heat flux. On coarse meshes the model shows an improvement of the results for both thermal and hydraulic parts with respect to a standard LES. On refined meshes, suitable for wall-resolved LES, the model suffers from a problem of double counting of modelled Reynolds stresses and heat fluxes because the RANS contribution does not naturally disappear as the mesh resolution increases.},
keywords = {Fuel rod bundle, hybrid RANS/LES, LES, nuclear engineering},
url = {https://www.escholar.manchester.ac.uk/uk-ac-man-scw:93444},
author = {Stefano Rolfo}
}
@mastersthesis {105,
title = {Large Eddy Simulation with the unstructured collocated arrangement},
volume = {PhD Thesis, The University of Manchester},
year = {2006},
school = {University of Manchester},
address = {Manchester},
abstract = {Several industrial applications of CFD, such as thermal fatigue, aero-acoustic
noise or fluid-structure interaction need to capture the unsteady behaviour of an
incompressible flow. Large Eddy Simulation is the only reasonable approach in
CFD to obtain a time-dependent solution, as well demonstrated on academic cases.
However, performing LES on fully unstructured finite-volume grids, as required for
complex industrial geometries, as well as to locally adapt the grid resolution to the
large spatial variations of turbulent scales, remains challenging. The main purpose
of the present work is to deal with the collocated arrangement implemented in the
in-house {\textasciiacute}Electricit{\textasciiacute}e De France (EDF) code Code Saturne and to show whether
reasonable LES computations are feasible with this discretization.
Several numerical issues such as numerical dissipation are first analyzed in a
discrete sense. It is found that the Rhie and Chow interpolation, widely used in all
the collocated approaches, introduces a numerical dissipation which drains energy
equally at all the wave-numbers. Removing this interpolation on regular Cartesian
grids allows, with a second order Crank-Nicolson scheme and sub-iterations on the
predictor-corrector algorithm for pressure/velocity coupling, to strictly conserve
kinetic energy. Nevertheless, the interpolation is maintained as it has a stabilizing
effect on skewed grids and as it avoids odd-even decoupling phenomenon. It is also
found that a {\textquoteright}symmetrical{\textquoteright} formulation allows to strictly conserve kinetic energy for
the convection term. The use of this formulation alters the second order precision
of the code. Thus, a second order approach for the convection term is kept with
implicit gradient reconstruction for non-orthogonal grids. Finally, sub-iterations
on the predictor-corrector algorithm for pressure/velocity coupling are retained as
this allows to reduce time splitting errors.
A particular attention is then paid to the Decaying Isotropic Turbulence in
order to identify the implicit filter induced by the discretization and to find the
appropriate Smagorinsky constant. It is found that the implicit filter induced by
the numerical discretization with a Smagorinsky model resembles to a Gaussian
filter with a filter-width equal to 2h where h is the grid-spacing in a regular mesh.
The value of the Smagorinsky constant is between 0.16 and 0.18 what corresponds
to consensual values found in the literature for highly accurate discretizations.
The explicit filter employed for the dynamic model is a smoothing operator that
involves all the neighbours of a cell which share a node with it. The filter-width
of this explicit filter is equal, on uniform meshes, to 3h. The averaging of the
Smagorinsky constant is done for its numerator and denominator separately. It
is also shown that local averaging gives reasonable results with the DIT which
is encouraging for industrial simulations in which no homogeneous direction is
available.
The last two academic cases to be tested are the standard and the oscillating
channel flows. After usual tests on structured Cartesian meshes, the ability of nonconforming
meshes to adapt the resolution large eddy scale variations at the wall is
pointed out. The global over-estimation of the mean velocity often observed with Cartesian meshes is cured by introducing local refinements in the near-wall region
using the capabilities of a collocated approach to naturally handle non-conforming
meshes. This solution is very promising to run industrial cases at moderate to high
Reynolds numbers without artificial wall functions. To conclude the channel flow
simulations, a distributed non-conforming mesh is created following the behaviour
of the Kolmogorov scales in each direction in order to obtain a very fine mesh compatible
with a Direct Numerical Simulation resolution but with a lower number of
computational cells than in the conforming cases. The results are very satisfactory
compared to previous DNS calculations on structured grids. This capability can
be exploited to run DNS calculations at higher Reynolds numbers with much less
nodes than in the structured case.
Finally, The potential of LES to predict complex vortical separation is reported
using a 3D axi-symmetric bump considered very challenging by the CFD
community as all Reynolds Averaged Navier-Stokes attempts totally failed. The
calculations give satisfactory quantitative results. The main physical structures
observed in the experiment are captured. The quantitative results are globally
satisfactory except for the wall-normal component of the velocity which is far from
the experimental results and for the Reynolds stresses which are overestimated.},
url = {http://cfd.mace.manchester.ac.uk/coffee/papers/phdSofian.pdf},
author = {Sofiane Benhamadouche}
}
@article {Benhamadouche2003470,
title = {LES, coarse LES, and transient RANS comparisons on the flow across a tube bundle},
journal = {International Journal of Heat and Fluid Flow},
volume = {24},
number = {4},
year = {2003},
note = {Selected Papers from the Fifth International Conference on Engineering Turbulence Modelling and Measurements},
pages = {470 - 479},
abstract = {The cross-flow in a staggered tube bundle is computed with an LES and a transient Reynolds stress transport model (RSTM) in 2D and 3D, with two levels of grid refinement. The numerical method is based on a finite volume approach on unstructured grids using a collocated arrangement for all the unknowns. It is shown that the LES results on the fine mesh are comparable to a DNS and experiments and reasonable agreement is still achieved with a coarse mesh. The RSTM also produced satisfactory results in 3D but showed no advantage over the LES when the grid was coarsened. The 2D RSTM, which produced strong vortex shedding, was found to be physically unreasonable.},
keywords = {Finite volume method},
issn = {0142-727X},
doi = {10.1016/S0142-727X(03)00060-2},
url = {http://www.sciencedirect.com/science/article/pii/S0142727X03000602},
author = {S. Benhamadouche and Laurence, D}
}