An experimental study of hydrogen combustion in hot air flows has been conducted in the framework of the LAPCAT-II European project, using a new Dual Mode Ramjet combustor (ONERA-LAERTE facility). Experiments have been carried out for wall injection of fuel in a Mach = 2 vitiated air flow for P 0 = 0.4 MPa and 1356 K < T 0 < 1712 K. The effect of operating conditions on combustion has been investigated. The temperature threshold necessary to observe supersonic combustion has also been determined and the effect of equivalence ratio on thermal choking has been explored. Complementary to pressure profile measurements, images of the combustion have been recorded using a camcorder and, in some cases, ICCD imaging has been obtained. Numerical simulations of this experiment are also presented and the vitiation effects are numercialy investigated. Nomenclature a = speed of sound TBC = thermal Barrier Coating DMR = dual mode ramjet Yi = mass fraction of i specie E.R. = equivalence ratio YSZ = yttria stabilized zirconia M = Mach number ρ = density m i = mass flow of i specie γ = adiabatic index P 0 = total pressure [i] = mole fraction of i specie T 0 = total temperature 0 (index) = reservoir conditions T w = wall temperature ∞ (index) = freestream conditions

The three-dimensional modal linear stability analysis is performed for the near-wall flow of a full-scale generic hypersonic vehicle forebody at flight Mach numbers 4, 6, and 8, at different angles of attack. The mean flow is computed with a Navier-Stokes commercial code. A physically sound, computationally efficient original method is proposed to define the integration path in the e N method. It has a significant impact on the computed N factors. The entropy-layer effect on the flow instability is analyzed in the framework of Lees and Lin's asymptotic theory. The entropy layer introduces an additional unstable mode, for which N 4. Results show that crossflow instability is dominant at Mach 6 and 8, whereas Mack's oblique first mode prevails at Mach 4. This mode is stabilized by a radiating wall, compared with an adiabatic one. Mack's second mode is also present at Mach 8. In any case, none of the instability modes that have been found is strong enough to provoke a natural transition in flight by itself: computed N factors do not exceed 10. Attempts to correlate the results with the Re =M e Const criterion are discussed.Nomenclature a = speed of sound, m=s C p , = heat capacity at constant pressure, J=kg K C v = heat capacity at constant volume, J=kg K f = frequency, Hz h = enthalpy per unit mass, J=kg k = thermal conductivity, W=m K k = wave vector (real), 1=m P = pressure, Pa r = C p C v , gas constant, J=kg K T = temperature, K t = time, s U, V, W = mean-flow components along x, y, and z, m=s V g = group velocity vector, m=s V ' = phase velocity, m=s W = molecular weight of species , kg=kmol X, Y, Z = coordinates in the global reference frame attached to the vehicle, m x, y, z = streamwise, transverse (normal to the wall), and spanwise coordinates, m X = mole fraction of species , = wave numbers (complex) in the x and z directions, 1=m = displacement thickness, m = momentum thickness, m g = direction of V g = viscosity, kg=m s = =, diffusivity, m 2 =s = density, kg=m 3 = amplification vector (real), 1=m = compressibility factor = direction of k = direction of ! = (real) pulsation, 1=sSubscripts M = maximum value (envelope method) u = unity w = value at the wall 1 = value at infinity, static value Superscripts e = value in the freestream, outside the boundary layer N = exponent in the e N method

Reactive and non-reactiveReynolds-averaged Navier-Stokes (RANS) simulations of hydrogen injection into a confined transverse supersonic flow of vitiated air are conducted. The corresponding conditions were studied in the LAPCAT-II combustor. We consider two operating conditions, which differ in the value of the momentum ratio between the hydrogen and vitiated air inlet streams, thus leading to two distinct values of the equivalence ratio (ER). For its smallest value, smooth combustion develops subject to a preliminary thermal runaway period, while for its largest value, combustion is more strongly intertwined with shock wave dynamics and boundary layer separation. Special emphasis is placed on the possible effects of wall roughness on this reactive flow development. One amongst the conclusions of preliminary computational analyses of the present flowfield was that it may play a significant role on combustion development. This is firmly confirmed in the present study, which takes explicitly the influence of wall roughness into account within the equivalent sand grain modeling framework. For the largest ER value, the combustion stabilization mechanism is found to change dramatically whether roughness is taken into account or not. Its influence is assessed through a detailed comparison with available experimental data.