JID:AESCTE AID:5081 /FLA [m5G; v1.255; Prn:1/04/2019; 16:24] P.1(1-11) Aerospace Science and Technology ••• (••••) •••–••• Contents lists available at ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 Implicit large eddy simulation of vitiation effects in supersonic air/H 2 combustion Mehmet Karaca a,∗,1 , Song Zhao a,2 , Ivan Fedioun a , Nicolas Lardjane b a ICARE-CNRS, 1c avenue de la Recherche Scientifique, F-45071 Orléans cedex 2, France b CEA, DAM, DIF, F-91297 Arpajon, France a r t i c l e i n f o a b s t r a c t Article history: Received 12 July 2018 Received in revised form 27 March 2019 Accepted 28 March 2019 Available online xxxx Keywords: Vitiation Implicit LES Turbulent combustion Non-premixed flames This paper presents and discusses Implicit Large Eddy Simulation (ILES) results of vitiation effects in ground tests of supersonic air/H 2 combustion. This work is useful for realistic extrapolation of ground test data to flight conditions. The high-enthalpy flow configuration retained, typical of scramjet engines, is the Mach 2 LAERTE combustion chamber of the French aerospace lab ONERA. The supersonic air co-flow is preheated by burning a small amount of hydrogen in oxygen-enriched air. Stable numerical simulations of such high-speed turbulent shocked flows require dissipative numerics that interact with molecular diffusion. The premature ignition in the case of vitiation by oxygen atom can be observed using reduced finite rate chemistry in the quasi-laminar approximation, i.e. without any subgrid combustion model, because the Damköhler number (ratio of turbulent to chemical time scale) is less than unity. Turbulent time scales are only moderately affected by vitiation, but chemical time scales are significantly reduced. © 2019 Published by Elsevier Masson SAS. 1. Introduction 1.1. Context and motivations of the study The last two decades have shown a renewed interest in hy- personic airbreathing flight. Examples are the American NASP and Hyper-X programs [1], and the French PREPHA (1992-1998), JAPHAR (1997-2002) and LEA (2003-2015) programs [2,3]. Ground- tests of the scramjet engine, representative of flight conditions, require the development of test rigs able to supply sustained high- speed and high-enthalpy air flow (typically M = 2, P tot = 1 MPa, T tot = 2000 K) for supersonic air/H 2 (or air/H 2 /CH 4 ) combustion. One of these such facilities is the supersonic test line of the LAERTE laboratory at ONERA Palaiseau, France [4,5] (Fig. 1). In most high-enthalpy blow-down wind-tunnels, like in the ex- periments of Tomioka et al. [6] or Kang et al. [7], pre-heated air flow representative of flight conditions is obtained from a combus- tion heater that burns hydrogen in oxygen-enriched air, resulting in the vitiation of the air stream by radicals like H, O, or OH, and products like H 2 O or NOx. It is therefore necessary to analyze the effects of vitiation on experiments in order to extrapolate ground- * Corresponding author. E-mail address: mkaraca@metu.edu.tr (M. Karaca). 1 Current address: Middle East Technical University, Ankara, Turkey. 2 Current address: Institut Pprime UPR 3346 CNRS, ISAE - ENSMA and University of Poitiers, France. Fig. 1. The LAERTE M = 2 combustion chamber at ONERA Palaiseau (figure from Falempin and Serre [2]). tests results to flight (clean) conditions. This can be achieved by using electrical heaters, e.g. Tatman et al. [8], at a higher energy expense or by numerical simulation. Electrical and storage heated facilities introduce thermodynamic non-equilibrium due to expan- sion. Clean conditions can be achieved adding water vapor (%2 molar) which is a fraction of amount in combustion heating to at- tain thermal equilibrium [9]. https://doi.org/10.1016/j.ast.2019.03.050 1270-9638/© 2019 Published by Elsevier Masson SAS.