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LES of a bi-periodic turbulent flow with effusion 25 orientation. Their direction of rotation corresponds to the one of the counter-rotating vortex pair observed in the time-averaged field (figure 15). In the instantaneous solution displayed in figure 16, they are more intense in one side of the jet (z < 0). They show the same spatial periodicity as the shear layer vortices (see figure 16, top view). Figure 17 displays the spanwise vorticity field over the centreline plane, at eight different instants. Two images are separated by δt = 0.0156 FTT. Two shear layers with negative spanwise vorticity (black colours in figure 17) are observed: the in-hole one separates the low-momentum and the jetting regions, and the leeward one is between the jet and the separation downstream the aperture. The windward shear layer exhibits positive values of spanwise vorticity. The in-hole shear layer destabilises and produces the in-hole hairpin vortices observed in figure 16. The Strouhal number of the in-hole structures, based on the vorticity thickness of the shear layer and the velocity difference is 0.14. The vortices are convected by the effusion flow (see the black arrows in figure 17) and they destabilise the windward shear layer at the same frequency of 1640 Hz. Small vortices with positive vorticity are then shed (white arrows); the Strouhal number in the windward shear layer is 0.54. The triggering of the windward vortices by the in-hole structures that are initiated near the hole inlet demonstrates that computing both sides of the wall is necessary to capture the FCFC flow physics. The in-hole vortices are convected outside the aperture but they are rapidly dissipated: none can be observed downstream of x ≈ 1.2 d. Note also that the leeward shear layer does not form any coherent structure. As a consequence, only structures with positive spanwise vorticity are observed outside the hole, on the injection side. This is different from what observed Tyagi & Acharya (2003) in their LES, in a comparable configuration, with a blowing ratio equal to unity. These authors interpret the vorticity fields from their computation as traces of hairpin structures shed from a thick shear layer observed in the downstream wall of the hole. Instead, the present results show that the shear layer vortices and the CVP form two different structures (figure 16). The slightly lower blowing ratio, the insufficient grid resolution and smaller computational domain (starting at the hole inlet) used in Tyagi & Acharya (2003) may explain these differences. Figure 17 also shows that the separation zones are regions of intense activity. 4.5. Flow organisation on the injection side: jet and wake In order to show how the jet behaves after having penetrated the crossflow, figure 18 displays contours and isolines of the time-averaged streamwise velocity , the streamwise RMS velocity u rms and the vertical RMS velocity v rms in the mid plane z = 0 and the time-averaged vertical velocity < V > in a plane normal to the crossflow direction and located three diameters downstream of the hole centre. The black line in figure 18(a) represents the trace of the cutting plane displayed in figure 18(d). Just after the outlet (1), the jet bends due to the crossflow (figure 18a) and separates from the wall. As reported in § 4.1, a zone of low velocity can be observed (2). Just downstream of the separation zone, under the jet, the velocity increases (3) because of the bypass of the jet by the main flow: part of the main flow is entrained between the jet and the wall. Figure 18(b) displays the variations of the streamwise RMS velocity. In the zone of strong shear in the hole (4), high levels of fluctuations are observed; they are mainly due to vortex shedding displayed in figure 17. In the wake of the jet, a second zone of high fluctuations can be noticed (5). This is also a region of strong shear, between the jet core and the separation zone. In this region, velocity fluctuations are mostly due to the variation of the jet position. Note that on the upstream side of the jet, the fluctuations are much smaller. Inclined jets in crossflow with moderate blowing ratio often show this type of behaviour because the velocity of the jet is close to that of the crossflow (Peet
26 S. Mendez and F. Nicoud Figure 17. Instantaneous views of the spanwise vorticity field ω z over the centreline plane. Reading is from left to right and top to bottom. Two images are separated by δt = 0.0156 FTT. The black arrows follow two consecutive in-hole vortices with negative vorticity; the white arrows show the two corresponding positive vortices triggered in the windward shear layer.
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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
Page 71 and 72: 3.2 Simulations des Grandes Echelle
Page 73 and 74: 3.3 Le code de calcul AVBP 3.3.1 As
Page 75 and 76: 3.3 Le code de calcul AVBP dans le
Page 77 and 78: 3.3 Le code de calcul AVBP de sa st
Page 79 and 80: Chapitre 4 Simulations numériques
Page 81 and 82: 4.1 Quelles simulations pour la mod
Page 83 and 84: 4.2 Choix de la méthode de simulat
Page 85 and 86: 4.2 Choix de la méthode de simulat
Page 87 and 88: 4.3 Sensibilité des simulations au
Page 99 and 100: 2 S. Mendez and F. Nicoud COMBUSTIO
Page 101 and 102: 4 S. Mendez and F. Nicoud (c) The i
Page 103 and 104: 6 S. Mendez and F. Nicoud CALCULATI
Page 105 and 106: 8 S. Mendez and F. Nicoud Name Numb
Page 107 and 108: 10 S. Mendez and F. Nicoud x/d z/d
Page 109 and 110: 12 S. Mendez and F. Nicoud main, it
Page 111 and 112: 14 S. Mendez and F. Nicoud 1.0 a 1.
Page 113 and 114: 16 S. Mendez and F. Nicoud ROWS 1 3
Page 115 and 116: 18 S. Mendez and F. Nicoud Figure 1
Page 117 and 118: 20 S. Mendez and F. Nicoud 30 ◦ 3
Page 119 and 120: 22 S. Mendez and F. Nicoud & Mahesh
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Page 125 and 126: 28 S. Mendez and F. Nicoud film, th
Page 127 and 128: 30 S. Mendez and F. Nicoud Region t
Page 129 and 130: 32 S. Mendez and F. Nicoud Expressi
Page 131 and 132: 34 S. Mendez and F. Nicoud geometri
Page 133 and 134: 36 S. Mendez and F. Nicoud (f) Two
Page 135 and 136: 38 S. Mendez and F. Nicoud Mendez,
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
Page 143 and 144: Simulations. The small-scale LES re
Page 145 and 146: chosen to compare with numerical re
Page 147 and 148: pressure drop of 41 Pa is effective
Page 149 and 150: Region total plate hole solid wall
Page 151 and 152: This equality is almost verified at
Page 153 and 154: V U σ V inj jet cotan(α′ ) V U
Page 155 and 156: PERIODIC Z INFLOW 1 WALL 24 OUTFLOW
Page 157 and 158: part of the plate. Downstream of th
Page 159 and 160: streamwise momentum flux. As a cons
Page 161 and 162: 8 Fric, T. and Roshko, A., “Vorti
Page 163 and 164: Discussion sur la modélisation de
Page 165 and 166: 20 15 10 y/d 5 0 -5 -10 0.0 0.2 0.4
Page 169 and 170: Primary flow (burnt gases) Secondar
Page 171 and 172: Figure 7: Nusselt number over the s
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the perforated plate. A Large-Eddy
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Les tableaux de flux permettent de
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Conclusion générale Dans cette é
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Conclusion générale En ce qui con
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Bibliographie AKSELVOLL, K. & MOIN,
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BIBLIOGRAPHIE CORON, X. 2001 Étude
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BIBLIOGRAPHIE HALE, C. A., PLESNIAK
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BIBLIOGRAPHIE LIEUWEN, T. & YANG, V
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BIBLIOGRAPHIE MOST, A. & BRUEL, P.
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BIBLIOGRAPHIE SCHILDKNECHT, M., MIL
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Annexes
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ARTIFICIAL VISCOSITY MODELS A.2.1 T
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ARTIFICIAL VISCOSITY MODELS - 4 th
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ARTIFICIAL VISCOSITY MODELS As a co
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ARTIFICIAL VISCOSITY MODELS 202
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