Conjugate heat transfer with Large Eddy Simulation for gas turbine components

CHT (Conjugate Heat Transfer) is a main design constraint for GT (gas turbines). Most existing CHT tools are developed for chained, steady phenomena. A fully parallel environment for CHT has been developed and applied to two configurations of interest for the design of GT. A reactive Large Eddy Simulations code and a solid conduction solver exchange data via a supervisor. A flame/wall interaction is used to assess the precision and the order of the coupled solutions. A film-cooled turbine vane is then studied. Thermal conduction in the blade implies lower wall temperature than adiabatic results and CHT reproduces the experimental cooling efficiency. To cite this article: F. Duchaine et al., C. R. Mecanique 337 (2009).     

Acoustically Induced Flashback in a Staged Swirl-Stabilized Combustor

This paper describes a joint experimental and numerical investigation of the interaction between thermoacoustics and flashback mechanisms in a swirled turbulent burner. An academic air/propane combustor terminated by a choked nozzle is operated up to 2.5 bars. Experiments show that the flame can stabilize either within the combustion chamber or flashback inside the injection duct, intermittently or permanently. The present study focuses on the mechanisms leading to flashback: this phenomenon can occur naturally, depending on the swirl level which can be adjusted in the experiment by introducing axial flow through the upstream inlet. It can also be triggered by acoustic waves, either through acoustic forcing or self-excited thermoacoustic instability. Flashback is difficult to study experimentally, but it can be investigated numerically using LES: in a first configuration, the outlet of the chamber is treated as a non-reflecting surface through which harmonic waves can be introduced. In this case, a 20 kPa acoustic forcing is sufficient to trigger permanent flashback after a few cycles. When the LES computational domain includes the choked nozzle used experimentally, no forcing is needed for flashback to occur. Self-excited oscillations reach high levels rapidly, leading to flame flashback, as observed experimentally. These results also suggest a simple method to avoid flashback by using fuel staging, which is then tested successfully in both LES and experiments.     

A Sub-Micromolar MraYAA Inhibitor with an Aminoribosyl Uridine Structure and a (S,S)-Tartaric Diamide: Synthesis,Biological Evaluation and Molecular Modeling

New inhibitors of the bacterial tranferase MraY are described. Their structure is based on an aminoribosyl uridine scaffold, which is known to be important for the biological activity of natural MraY inhibitors. A decyl alkyl chain was introduced onto this scaffold through various linkers. The synthesized compounds were tested against the MraY_AA transferase activity, and the most active compound with an original (S,S)-tartaric diamide linker inhibits MraY activity with an IC₅₀ equal to 0.37 µM. Their antibacterial activity was also evaluated on a panel of Gram-positive and Gram-negative strains; however, the compounds showed no antibacterial activity. Docking and molecular dynamics studies revealed that this new linker established two stabilizing key interactions with N190 and H325, as observed for the highly potent inhibitors carbacaprazamycin, muraymycin D2 and tunicamycin.     

Recent advances in amino acid analysis by CE

This paper describes a number of articles that have been published on amino acid (AA) analysis using CE during the period from June 2005 to May 2007. This review article follows the format of the previous articles of Smith (Electrophoresis 1999, 20, 3078-3083), Prata et al.. (Electrophoresis 2001, 22, 4129-4138), and Poinsot et al.. (Electrophoresis 2003, 24, 4047-4062 and Electrophoresis 2006, 27, 176-194). Several new developments in AA analysis with CE are reported describing the use of laser-emitting diodes for LIF, MS, and chips. In addition, we describe articles concerning clinical studies and neuroclinical applications.     

Hydrogen: a good partner for rhodium‐catalyzed hydrosilylation

The influence of hydrogen pressure on the hydrosilylation of ketones catalyzed by [((S)‐SYNPHOS)Rh(nbd)]OTf has been studied. We have notably demonstrated that hydrogen significantly affected the outcome of the reaction while not being consumed as stoichiometric reducing agent. In THF, diethyl ether or toluene, the hydrogen pressure exceedingly accelerated the hydrosilylation reaction and preserved or even improved the enantioselectivity of the process. In CH₂Cl₂, the rhodium catalyst also showed generally higher catalytic activity under hydrogen pressure. Most serendipitously, several ketones were found to give products of absolute opposite configuration upon performing the hydrosilylation under argon atmosphere or under hydrogen pressure. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of Two-Fluid Methods for Large Eddy Simulation of Spray Combustion in Gas Turbines

An extension of the large eddy simulation (LES) technique to two-phase reacting flows, required to capture and predict the behavior of industrial burners, is presented. While most efforts reported in the literature to construct LES solvers for two-phase flow focus on Euler–Lagrange formulation, the present work explores a different solution (‘two-fluid’ approach) where an Eulerian formulation is used for the liquid phase and coupled with the LES solver of the gas phase. The equations used for each phase and the coupling terms are presented before describing validation in two simple cases which gather some of the specificities of real combustion chamber: (1) a one-dimensional laminar JP10/air flame and (2) a non-reacting swirled flow where solid particles disperse (Sommerfeld and Qiu, Int. J. Multiphase Flow 19(6):1093–1127, 1993). After these validations, the LES tool is applied to a realistic aircraft combustion chamber to study both a steady flame regime and an ignition sequence by a spark. Results bring new insights into the physics of these complex flames and demonstrate the capabilities of two-fluid LES.     

Numerical and analytical investigation of the indirect combustion noise in a nozzle

Analytical and numerical assessments of the indirect noise generated through a nozzle are presented. The configuration corresponds to an experimental setup operated at DLR by Bake et al. (2008) where an entropy wave is generated upstream of the nozzle by means of an electrical heating device. Both 3-D and 2-D axisymmetric simulations are performed to demonstrate that the experiment is mostly driven by linear acoustic phenomena, including pressure wave reflection at the outlet and entropy-to-acoustic conversion in the accelerated regions. Results show that the acoustic impedance downstream of the nozzle must be accounted for appropriately in order to recover the experimental pressure signal. A good agreement is also obtained with a purely analytical assessment based on the Marble and Candel compact nozzle approximation. To cite this article: M. Leyko et al., C. R. Mecanique 337 (2009).     

231Pa Mössbauer resonance in Pa metal

The Mössbauer resonance of the 84.2 keV transition in ²³¹Pa has been measured for an absorber of Pa metal at 4.2 K with respect to a source of ThO₂ at 4.2 and 65 K. The resulting nuclear parameters are compared with calculations based on the Nilsson model. The electric field gradient in Pa metal is |eq_z| = (2.05 ± 0.15)} 10¹⁸ V/cm².     

Large eddy simulation of piloting effects on turbulent swirling flames

Pilot flames, created by additional injectors of pure fuel, are often used in turbulent burners to enhance flame stabilization and reduce combustion instabilities. The exact mechanisms through which these additional rich zones modify the flame anchoring location and the combustion dynamics are often difficult to identify, especially when they include unsteady hydrodynamic motion. This study presents Large Eddy Simulations (LES) of the reacting flow within a large-scale gas turbine burner for two different cases of piloting, where either 2 or 6% of the total methane used in the burner is injected through additional pilot flame lines. For each case, LES shows how the pilot fuel injection affects both flame stabilization and flame stability. The 6% case leads to a stable flame and limited hydrodynamic perturbations in the initial flame zone. The 2% case is less stable, with a small-lift-off of the flame and a Precessing Vortex Core (PVC) in the cold stabilization zone. This PVC traps some of the lean cold gases issuing from the pilot passage stream, changes the flame stabilization point and induces instability.