The mixing of eight isothermal jets issuing in a fully developed circular pipe flow is investigated by means of laser Doppler anemometry, particle image velocimetry, and planar laser induced fluorescence techniques. Two values of the momentum ratio are considered. Unsteady and steady flow patterns are analyzed. Characteristic frequencies are deduced from spectral analysis. Velocity and scalar concentration fields are compared. The mean centerline concentration decay is characterized. The analysis of the flow instabilities is focused on the wake-type structures downstream of the jets and the shear layer structures appearing between the jet and the main flow. The results on the wake-type structures are consistent with previous observations done on a single jet. In particular, the influence of the velocity ratio on the signal-to-noise ratio is confirmed. The Strouhal number associated with the shear layer structure depends on the velocity ratio and on the Reynolds number. The comparison between the velocity and concentration fields confirms the difference in the jet trajectories deduced from these two fields. The detailed analysis of the concentration field gives useful information on the influence of the confinement on the jets' behavior. Nomenclature b = distance from the maximum concentration location where Cx; b 0:5C max x, m b in = b value toward the wall, m b out = b value toward the pipe axis Cx; y; z = concentration C max x = maximum concentration value in the section D = pipe diameter, m d = jet diameter, m J = momentum flux ratio ( jet U 2 jet = o U 2 o ) k = kinetic turbulence level, m=s 2 Q m axial = mass flow rate of the crossflow, kg=m 3 Q m jets = mass flow rate of the jet flow,kg=m 3 R = jet-to-crossflow-velocity ratio (U jet =U o ) r; ; x = polar coordinate Re jets = Reynolds number calculated from the jet diameter and the jet bulk velocity Re o = Reynolds number calculated from the pipe diameter and the upstream bulk velocity s = spatial coordinate along the jet trajectory, m St j = Strouhal number calculated from the jet diameter and the jet bulk velocity St o = Strouhal number calculated from the jet diameter and the upstream bulk velocity U jets = jet bulk velocity, m=s U o = main flow bulk velocity, m=s x; y; z = Cartesian coordinate y max = distance from the wall where C max x is reached

An experimental and numerical study is carried out on a cooling film issuing from a multiperforated wall of a simplified combustor. The objectives of this work are to achieve a better understanding of the dynamics of the film and to construct an experimental database on a simplified geometry in order to test numerical models. A parametric study of film cooling efficiency based on the direction of the cooling air injection is presented and shows that a swirling injection greatly enhances the cooling efficiency. As accounting for multiperforated walls in numerical simulations cannot be done at the jets scale because of computing resources, in this article are presented RANS computations performed using a uniform boundary condition to provide the injection of coolant. Two injection models are applied on this boundary and numerical results are compared to experimental data in the recovery region. The standard model is shown to be totally inappropriate while the multiperforation model delivers promising results although some weaknesses appear very close to the wall.

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