Multiphase Flow LES Study of the Fuel Split Effects on Combustion Instabilities in an Ultra Low-NOx Annular Combustor

International audienceThis paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: (1) a gaseous type in the multipoint zone (MPZ) where acoustics generates vortex shedding, which then wrinkle the flame front, and (2) a multiphase flow type in the pilot zone (PZ) where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the PZ and mechanism 2) to assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using an analytical model validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations in the PZ, which strongly depend on the fuel split parameter. However, the correlation between acoustics and the global (pilot + multipoint) heat release fluctuations highlights no dependency on the fuel split staging. It suggests that vortex shedding in the MPZ, almost not depending on the fuel split, is the main feature controlling the flame dynamics for this engin

Calixarene-based amphiphiles : synthesis, self-assembly and interaction with DNA

The present doctoral thesis focused on the synthesis of amphiphilic calix[4]arenes, the study of their self-assembly properties at the air-water interface as Langmuir monolayers or in solution as nanoparticles and on the DNA-binding properties of the resulting self-assembled structures. The objective is to improve the understanding of the interaction of amphiphilic calixarene-based nanoparticles with DNA molecules, and to improve the comprehension of the effect of the calixarene structure: on the self-assembly of the amphiphilic calixarene as nanoparticles and on the interaction of the calixarene-based nanoparticles with DNA. The results reported in my PhD dissertation highlight the influence of the calixarene structure, on their self-assembly as Langmuir monolayer at the air-water interface and as nanoparticles in water. Moreover the binding mechanism between the DNA phospho-diester backbone and the self-assembled calix[4]arene is dependent of the number of recognition moieties but is also governed by a sequence dependent interaction mechanism

Modélisation de la combustion turbulente via une méthode de tabulation de la cinétique chimique détaillée couplée à des fonctions de densités de probabilité. Application aux foyers aéronautiques

Rapporteurs : Ken BRAY, Hui Ying WANGJury : Abdelkrim BOUKHALFA, Denis VEYNANTE, Michel CAZALENS, Luc VERVISCHA new modelisation of turbulent combustion is proposed with detailed chemistry and PDFs. The objective is to capture temperature and species concentrations, mainly the CO. The PCM-FTC model, Presumed Conditional Moment – Flame Tabulated Chemistry, is based on the tabulation of laminar premixed and diffusion flames to capture partial premixing present in aeronautical engines. The presumed PDFs is introduced to predict averaged values. The tabulation method is based on the analysis of the chemical structure of laminar premixed and diffusion flames. Hypothesis are presented, tested and validated with Sandia experimental data jet flames. Then, the model is introduced in a turbulent flow simulation software. Three configurations are retained to quantify the level of prediction of this formulation : the D and F-Flames of Sandia and lifted jet flames of methane/air of Stanford. A good agreement is observed between experiments and simulations. The validity of this method is then demonstrated.Une modélisation de la combustion turbulente est proposée avec une chimie détaillée et des PDFs, afin de quantifier les concentrations des espèces chimiques (dont le CO). Le modèle PCM-FTC, Presumed Conditional Moment – Flame Tabulated Chimistry, est basé sur des méthodes de tabulations de flammes laminaires prémélangées et de diffusion pour prédire les phénomènes de prémélange partiel présents dans les foyers aéronautiques. La méthode de tabulation est basée sur une analyse de la structure chimique des flammes laminaires prémlélangées et de diffusion. Les hypothèses formulées dans cette modélisation sont testées et validées. Le modèle est alors implanté dans un logiciel de simulation des écoulements turbulents. Trois configurations sont retenues pour quantifier le pouvoir prédicteur de ce type d'approche : les flammes jets turbulentes de Sandia (D et F) et les flammes suspendues de méthane/air de Stanford. Les comparaisons numériques et expérimentales ont permis de valider la méthode

Influence de la qualite des semences de luzerne sur la vigueur des plantules

National audienc

Three facets of turbulent combustion modelling: DNS of premixed V-flame, LES of lifted nonpremixed flame and RANS of jet-flame

International audienc

Sequence-Specific DNA Interactions with Calixarene-Based Langmuir Monolayers

The interactions of an amphiphilic calixarene, namely <i>p</i>-guanidino-dodecyloxy-calix­[4]­arene, <b>1</b>, self-assembled as Langmuir monolayers, with short double stranded DNA, were investigated by surface pressure–area (π–<i>A</i>) isotherms, surface ellipsometry and Brewster angle microscopy (BAM). Three DNA 30mers were used as models, poly­(AT), poly­(GC) and a random DNA sequence with 50% of G:C base pairs. The interactions of these model DNA duplexes with <b>1</b>-based Langmuir monolayers were studied by measuring compression isotherms using increasing DNA concentrations (10^–6, 10^–5, 10^–4, and 5 × 10^–4 g L^–1) in the aqueous subphase. The isotherms of <b>1</b> showed an expansion of the monolayer with, interestingly, significant differences depending on the duplex DNA sequence studied. Indeed, the interactions of <b>1</b>-based monolayers with poly­(AT) led to an expansion of the monolayer that was significantly more pronounced that for monolayers on subphases of poly­(GC) and the random DNA sequence. The structure and thickness of <b>1</b>-based Langmuir monolayers were investigated by BAM and surface ellipsometry that showed differences in thickness and structure between a monolayer formed on pure water or on a DNA subphase, with here again relevant dissimilarities depending on the DNA composition

Langmuir-Blodgett monolayer stabilization using supramolecular clips

We introduce the concept of stabilization of Langmuir-Blodgett (LB) films using dicarboxylate supramolecular clips, as demonstrated by Langmuir isotherms, spectroscopic ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements

High-cell-density cultivation of recombinant Escherichia coli, purification and characterization of a self-sufficient biosyntheticoctane ω-hydroxylase

International audienceWe have recently described the biocatalytic characterization of a self-sufficent biosynthetic alkane hydroxylase based on CYP153A13a from Alcanivorax borkumensis SK2 (thereafter A13-Red). Despite remarkable regio- and chemoselectivity,A13-Red suffers of a difficult-to-reproduce expression and moderate operational stability. In this study, we focused our efforts on the production of A13-Red using high-cell-density cultivation (HCDC) of recombinant Escherichia coli. We achieved 455 mg (5,000 nmol) of functional enzyme per liter of culture. Tight control of cultivation parameters rendered the whole process highly reproducible compared with flask cultivations. We optimized the purification of the biocatalyst that can be performed in either two or three steps depending on the application needed to afford A13-Red up to 95 % homogeneous.We investigated different reaction conditions and found that the total turnover numbers of A13-Red during the in vitro hydroxylation of n-octane could reach up to 3,250 to produce 1-octanol (1.6 mM) over a period of 78 h

Innovations in surgery to perform an ovarian drilling

International audienceBackground: Ovarian drilling is a surgical technique for patients with dysovulatory polycystic ovarian syndrome. It is proposed as a second-line treatment in case of failure of medical treatment with Clomiphene citrate, Metformin or Letrozole. The 2020 Cochrane study comparing gonadotrophin stimulation and drilling has found the same pregnancy rate in both cases. The literature review concludes that 50% of spontaneous ovulation occurs in the first three months after drilling and 80% of pregnancy occurs in the following year. Ovarian drilling has also an impact on androgen excess and metabolic syndrome. Aims: To update on the different surgical techniques to perform an ovarian drilling: surgical approach, energy used, operative risks. Techniques: The objective of an ovarian drilling is to destroy 5% of the ovarian stroma. It is recommended to perform 8 to 10 perforations in each ovary with bipolar energy. Laser C02 and monopolar energy can be used but increase the risk of adhesion. The surgical approach is actually laparoscopic. Abdominal laparoscopy or transvaginal laparoscopy by vNOTES can be performed. The advantage of the second one is to provide an easier access to the pelvic cavity in case of obesity and patient have no abdominal scare. Both laparoscopic approaches allow an evaluation of tubal patency and adhesiolysis or fimbrioplasty. That it's not the case of an alternative technique: the fertiloscopy, due to coaxial instrumentation in spite of less rate of post-operative adhesions. Operative risks are abdominal adhesions, damage to neighboring organs and due to the general anesthesia. Conclusion: Different surgical techniques exist to perform an ovarian drilling. The surgeon can choose the one that he masters best and that will involve the least risk for the patient. It is recommended to use bipolar energy