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α σ ϕ UM1 or UM2 C D V j P suc ,P inj N inj ρ suc ,T suc N suc Y ksuc Figure 8. Schematic of the coupling procedure. Dotted lines denote the external input parameters needed by the models: only the geometrical details (porosity and hole angles) and a law for the discharge coefficient C D have to be provided. IV. Application of the uniform model in the LARA configuration The models proposed in section III.B, UM1 and UM2, are implemented in the AVBP code (section IIA) and tested in the case of the LARA experiment. Fig. 9 presents the computational domain of the large-scale large-eddy simulations performed for the a posteriori validation. It consists in two channels (height h = 0.12 m) separated by a plate that is perforated over a streamwise distance of 2.7 h. It has been decided to locate the inflows 6 h upstream of the perforated part of the plate. Fluid coming from channel 2 is injected in channel 1 through the multi-perforated plate to mimic the effusion of cooling air into combustion products. The side walls of the experiment have been replaced by periodic conditions in the spanwise direction z. In the simulation, the perforated part of the wall is replaced by the coupled boundary condition described in section III.C. The grid contains 121 × 31 × 31 hexahedral nodes for channel 1 and 121 ×21 ×31 hexahedral nodes for channel 2. This difference is due to the lower values of Reynolds numbers imposed in channel 2 in the LARA experiment. In the experiment, far enough from the side walls, the velocity profiles upstream of the perforated zone correspond to fully developed channel flow profiles. In the simulation, imposing the mean streamwise velocity profile at the inlet is not a satisfying approach: the flow needs a too long distance to destabilize and recover the characteristics of a fully turbulent channel. Thus it has been decided to accelerate this transition by using the Random Flow Generation (RFG) algorithm 41,42 to make the fluid velocity vary in time and space at the 17 of 26
PERIODIC Z INFLOW 1 WALL 24 OUTFLOW 1 INFLOW 2 WALL LINER WALL 24 OUTFLOW 2 WALL 144 64.8 79.2 Figure 9. Large-scale computational domain for the a posteriori testing of the liner model. Dimensions are specified in hole diameters. 36 inlets. This method reproduces the effect of an incoming turbulent field thanks to the superposition of harmonic functions (100 modes projected along the three directions) with characteristic length-scales directly related to the geometry and the grid. This method has already been successfully employed in various simulations with AVBP. 34,43 Ideally the fluctuating velocity profiles and the cross-correlation u i u j imposed at the simulation inlets should be the values measured in the experiment. However, in the LARA experiment, only a two-component laser-doppler anemometry system has been used: the data involving the spanwise component W is unknown. To overcome this problem, it has been decided to generate the characteristics of the inflow numerically. A periodic channel flow simulation with wall function boundary conditions is performed. The wall function boundary conditions have been developed in Schmitt et al. 33 in AVBP and validated in the case of a periodic channel flow; they used a logarithmic law to predict friction at the wall from the first off-wall point. Two periodic simulations have been performed to generate the statistics needed for the inflows of the top and bottom channels of the computational domain (Fig. 9). The dimensions of the calculation domains in the periodic simulations in millimeters are (3h,h,2h). Statistics (mean and fluctuating velocities, Reynolds stresses) are obtained from the averaging of eleven independent solutions. For consistency reasons, periodic simulations are performed with exactly the same parameters as the large-scale computation: the numerical parameters, grid spacing, spatial/temporal schemes, sub-grid scale model and wall function are identical. The NSCBC method 44 is used for the inflow and outflow boundary conditions in the domain. The pressure at the outflows is imposed, with a pressure at outlet 2 (Fig. 9) superior to the one imposed at outflow 1 to ensure the injection of fluid from channel 2 to channel 1. The wall-function boundary conditions 33 are used for the solid walls in the large-scale computation, the first off-wall point being located approximately at y + = 45. Computations have been run over 16 flow through times (FTT): the flow through time is based on the length of the channels and the crossflow velocity in channel 1, U 1 . Time averages are accumulated over 8 FTT. Fig 10 and 11 present the time-averaged streamwise 18 of 26
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UNIVERSITE MONTPELLIER II SCIENCES
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Table des matières Remerciements 7
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Remerciements Cette thèse a été
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Liste des symboles Lettres romaines
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Introduction générale La volonté
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Chapitre 1 Contexte industriel et s
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1.1 Les turbines à gaz pour les tu
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1.1 Les turbines à gaz a) b) GAZ C
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1.2 La simulation numérique des é
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1.3 Objectifs et plan de la thèse
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Chapitre 2 L’écoulement autour d
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2.1 Présentation de la configurati
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2.2 Perte de charge au passage d’
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2.3 La multi-perforation : aspects
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2.4 Caractérisation aérodynamique
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2.5 Modélisation de la multi-perfo
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Chapitre 3 Simulations des grandes
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3.2 Simulations des Grandes Echelle
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3.3 Le code de calcul AVBP 3.3.1 As
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3.3 Le code de calcul AVBP dans le
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3.3 Le code de calcul AVBP de sa st
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Chapitre 4 Simulations numériques
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4.1 Quelles simulations pour la mod
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4.2 Choix de la méthode de simulat
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4.2 Choix de la méthode de simulat
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4.3 Sensibilité des simulations au
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Chapitre 5 Simulations numériques
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2 S. Mendez and F. Nicoud COMBUSTIO
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4 S. Mendez and F. Nicoud (c) The i
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Page 137 and 138: Chapitre 6 Un modèle adiabatique p
Page 139 and 140: ρ Mass density, kg/m 3 P T V i τ
Page 141 and 142: cence of the jets. This is particul
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Page 147 and 148: pressure drop of 41 Pa is effective
Page 149 and 150: Region total plate hole solid wall
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Page 179 and 180: Conclusion générale En ce qui con
Page 181 and 182: Bibliographie AKSELVOLL, K. & MOIN,
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Page 185 and 186: BIBLIOGRAPHIE HALE, C. A., PLESNIAK
Page 187 and 188: BIBLIOGRAPHIE LIEUWEN, T. & YANG, V
Page 189 and 190: BIBLIOGRAPHIE MOST, A. & BRUEL, P.
Page 191 and 192: BIBLIOGRAPHIE SCHILDKNECHT, M., MIL
Page 193: Annexes
Page 196 and 197: ARTIFICIAL VISCOSITY MODELS A.2.1 T
Page 198 and 199: ARTIFICIAL VISCOSITY MODELS - 4 th
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Page 202: ARTIFICIAL VISCOSITY MODELS 202
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