Stabilization of a premixed laminar flame on a rotating cylinder

This paper investigates the stabilization of a laminar premixed flame on a rotating cylinder. Experiments and DNS are combined to analyze the effects of rotation on the flow topology and flame stabilization. Both experiment and simulation reveal that the usual stabilization pattern (two symmetric flame roots on both sides of the cylinder) is strongly affected by rotation. The flame roots positions on the upper and lower sides of the cylinder are modified with increasing rotation speeds. One of the two flame roots is quenched over a long region. The distance of the flame roots to the flameholder changes with the rotation speed until a bifurcation takes place: at a critical rotation speed, the flame roots merge, and the flame stabilizes upstream of the cylinder. DNS results are used to explain the flame topologies observed experimentally

Joint experimental and numerical study of the influence of flame holder temperature on the stabilization of a laminar methane flame on a cylinder

The mechanisms controlling laminar flame anchoring on a cylindrical bluff-body are investigated using DNS and experiments. Two configurations are examined: water-cooled and uncooled steel cylinders. Comparisons between experimental measurements and DNS show good agreement for the flame root locations in the two configurations. In the cooled case, the flame holder is maintained at about 300 K and the flame is stabilized in the wake of the cylinder, in the recirculation zone formed by the products of combustion. In the uncooled case, the bluff-body reaches a steady temperature of about 700 K in both experiment and DNS and the flame is stabilized closer to it. The fully coupled DNS of the flame and the temperature field in the bluff-body also shows that capturing the correct radiative heat transfer from the bluff-body is a key ingredient to reproduce experimental results

Phosphor thermometry on a rotating flame holder for combustion applications

This study presents a method to measure wall temperatures of a rotating flame holder, which could be used as a combustion control device. Laser induced phosphorescence (LIP) is found to be a reliable technique to gather such experimental data. The paper first investigates how the coating (thickness, emissivity and lifetime) influence the flame stabilization. While the low thermal conductivity of the coating is found to induce a temperature dif- ference of 3 − 5 K, the emissivity increases by 40%. Nevertheless, the transient and steady-state flame location are not affected. Second, because temperature measurements on the rotating cylinder are likely to fail due the long phosphor lifetimes, we modify the classical point-wise arrangement. We propose to illu- minate a larger area, and to correct the signal with a distortion function that accounts for the displacement of the target. An analytical distortion function is derived and compared to measured ones. It shows that the range of mea- surements is limited by the signal extinction and the rapid distortion function decay. A diagram summarizes the range of operating conditions where mea- surements are valid. Eventually, these experimental data are used to validate direct numerical simulations. A sensitivity analysis shows that the precision of the technique still gives a good agreement for the flame location

Experimental and numerical investigation of flames stabilised behind rotating cylinders: interaction of flames with a moving wall

Steady methane/air laminar premixed flames stabilised on a cylindrical bluff body subjected to a continuous rotation are analysed using joint direct numerical simulations (DNS) and experiments. DNS are carried out using a 19 species scheme for methane/air combustion and a lumped model to predict the cylinder temperature. Rotation of the cylinder induces a symmetry breaking of the flow, and leads to two distinct flame branches in the wake of the cylinder. DNS are validated against experiments in terms of flame topologies and velocity fields. DNS are then used to analyse flame structures and thermal effects. The location and structure of the two flames are differently modified by rotation and heat transfer: a superadiabatic flame branch stabilises close to the hot cylinder and burns preheated fresh gases while a subadiabatic branch is quenched over a large zone and anchors far downstream of the cylinder. Local flame structures are shown to be controlled to first order by the local enthalpy defect or excess due to heat transfer between the cylinder and the flow. An analysis of the local wall heat flux around the cylinder shows that, for low rotation speeds, the superadiabatic flame branch contributes to wall heat fluxes that considerably exceed typical values found for classical flame/wall interactions. However, for high rotation speeds, fluxes decrease because the cylinder is surrounded by a layer of burned gases that dilute incoming reactants and shield it from the flame

A Mesh Adaptation Strategy to Predict Pressure Losses in LES of Swirled Flows

The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013) / ERC Grant Agreement ERC-AdG 319067-INTECOCIS

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe