Alexis Giauque

• PhD
• Professor (Associate) at École Centrale de Lyon

The development and application of a compressible hybrid lattice Boltzmann method to high Mach number supercritical and dense gas flows are presented. Dense gases, especially in Organic Rankine Cycle turbines, exhibit nonclassical phenomena that offer the possibility of enhancing turbine efficiency by reducing friction drag and boundary layer separ...

The tonal and broadband noise of an ultrahigh-bypass-ratio fan stage, which has been developed at École Centrale de Lyon, is studied using large-eddy simulations (LES). Wall-modeled LES of a periodic sector and a 360-deg full fan stage have been performed at approach conditions, which is a relevant operating point for aircraft noise certifications....

Large-Eddy Simulations (LES) results are used to track flow separation zones in a splittered vaned radial diffuser near the compressor best efficiency at high rotation speed. The topology analysis reveals some closed separations at the corner of the blade and hub or shroud surface. In addition, an open-closed flow separation at the main blade press...

The broadband noise generated within a fan-OGV stage and partly caused by the interaction between shockwaves and turbulent structures cannot be easily modelled due to the stochastic nature of the flow. High fidelity numerical methods are able to simulate with sufficient accuracy the characteristics of the flow. LES of the ECL5 fan/OGV stage are per...

This study aims at investigating real gas flow in the complex geometry of the Cambridge University annular turbine cascade using numerical simulations. The objectives include validating the numerical approach and understanding the loss mechanisms in this configuration. The numerical results are compared to experimental measurements obtained at vari...

In the present study, the broadband noise of an ultra high bypass ratio fan/OGV stage, developed at École Centrale de Lyon, is studied numerically. Wall-modeled large eddy simulations (LES) over a 360°full fan stage are performed for the first time, at approach conditions. The noise emissions in the fan stage are directly obtained by the fully comp...

Using a DNS database (available to the NICFD research community) including homogeneous isotropic turbulence (HIT), mixing layers and channel flows, the authors have developed a novel LES model for the Subgrid-Scale (SGS) turbulent Reynolds tensor based on artificial neural networks (ANN) with optimized hyperparameters. Particular attention has been...

Reynolds-averaged Navier-Stokes (RANS) simulations are performed for turbulent perfect and real gas flows (supersonic flat plate and compressible mixing layer) with available theoretical or numerical (DNS) reference results. The model assessment is focused on versions of the SA model which include density and compressibility corrections proposed in...

A detailed aeroacoustic analysis of the flow induced by the clearance between the fan tip and the shroud is performed in a scale-model fan stage of an Ultra High Bypass Ratio turbofan engine. Wall-modeled Large Eddy Simulation has been performed at approach condition, which corresponds to a fully subsonic operating point. The contributions of the t...

A scale model of a fan stage operating at approach condition is investigated using wall-resolved Large Eddy Simulations. The configuration is a state-of-the-art fan stage (rotor + stator) of an Ultra High Bypass Ratio turbofan engine, and the computational cost has been reduced by simulating a radial slice of a peri- odic sector. At low fan speeds...

In the present study, we analyze the broadband noise of an ultra high by-pass ratio fan/OGVstage developed at Ecole Centrale de Lyon. Wall-modeled large eddy simulations (LES) of aperiodic fan/OGV sector are performed at approach conditions on an unstructured grid thatis well refined for direct noise propagation. Comparisons between wall-resolved a...

Dans cette étude, le bruit propre d'un étage soufflante-redresseur (rotor + stator) d'un moteur d'avion est étudié en phase d'approche. Des simulations aux grandes échelles (SGE) résolues en paroi sont effectuées sur une tranche radiale d'un étage soufflante-redresseur à fort taux de dilution, l'ECL5, conçu à l'École Centrale de Lyon (ECL). En régi...

The fan stage of an aero-engine is a major contributor to the overall engine noise. ➢At approach conditions, the broadband noise becomes a major contributor to the fan noise.

https://hal.archives-ouvertes.fr/hal-03583335

The present work is devoted to the analysis and modeling of turbulence in flows of densegases (DG). The interest for these gases mainly comes from the Organic Rankine Cycles (ORC) turbine industry. ORCs rely on the so-called and widely used William Rankine’s cycle. The organic working fluid (instead of water) is expanded after being evaporated so a...

La formation d'une bulle de recirculation est souvent observée sur les pales de turbomachines en régime partiel. Pour ces régimes, la vitesse de l'écoulement est réduite, entrainant des angles d'attaque importants au niveau du bord d'attaque (BA) de la soufflante, et générant une séparation locale de l'écoulement et la formation d'une bulle de reci...

The present article investigates the effects of a BZT (Bethe-Zel'dovich-Thompson) dense gas (FC-70) on the development of turbulent compressible mixing layers at three different convective Mach numbers Mc = 0,1; 1,1 and 2,2. This study extends previous analysis conducted at Mc = 1,1 (Vadrot et al. 2020). Several 3D direct numerical simulation (DNS)...

Of interest to the research community dealing with real gas flows, this study analyzes the influence of the physical complexity of real gases on the amplitude of subgrid-scale (SGS) terms present in the filtered Navier–Stokes equations to be solved in large eddy simulations. The direct numerical simulation results of three academic configurations (...

In the present paper, large eddy simulations are performed to study two different mechanisms of Fan/OGV broadband noise: airfoil self-noise and turbulence interaction noise. Firstly, the current study focuses on the prediction of airfoil self-noise from a thin plate with a sharp trailing edge and a chord-based Reynolds number of the order of 106. T...

In the present paper, large eddy simulations are performed to study two different mechanisms of Fan/OGV broadband noise: airfoil self-noise and turbulence interaction noise. Firstly, the current study focuses on the prediction of airfoil self-noise from a thin plate with a sharp trailing edge and a chord-based Reynolds number of the order of 106. T...

It is known from the literature that Large Eddy Simulations of dense gas flows can prove very useful in order to better understand the behavior of friction losses in Organic Rankine Cycle turbines and expanders. Yet, no dedicated turbulence closure models exist for such flows. In this study, the authors lay the fondations for the development of tur...

This presentation provides the latest developments of the ANR EDGES project. By filtering DNS results of Homogeneous Isotropic Turbulence, it is shown that new subgrid-scale terms need to be modelled which have received no attention so far. This work is relevant in the context of LES and RANS simulations of ORC turbines.

In order to assess the specific characteristics of turbulence in dense gas flows with respect to ideal gas flows, Direct Numerical Simulations are performed for both FC-70 described using Martin-Hou Equation of State (EoS) and a reference ideal gas, in the case of a forced Homogeneous Isotropic Turbulence (HIT) configuration and of a temporal compr...

**Full text available at: https://hal.archives-ouvertes.fr/hal-02550908** ************ **Also check link: https://authors.elsevier.com/c/1azaoAQO4jKrD******* This article presents a detailed analysis of an improved weak recycling method used to generate turbulent inflow conditions for large-eddy simulations. Answering some of the points raised in...

Entropy noise corresponds to acoustic fluctuations generated inside gas-turbine engines when temperature (entropy) spots are accelerated by the mean flow. This type of noise currently faces growing interest because of its contribution to global aero-engine noise as well as its impact on combustion instabilities. In the present article, a two-dimens...

This study investigates the effects of a BZT (Bethe-Zel'dovich-Thompson) dense gas (FC-70) on the development of a turbulent compressible mixing layer at a convective Mach number M c = 1.1. 3D direct numerical simulations (DNS) are performed both with FC-70 and air. The initial thermodynamic state for FC-70 lies inside the inversion region where th...

Analysis of turbulence characteristics in a temporal dense gas compressible mixing layer using direct numerical simulation - Volume 893 - Aurélien Vadrot, Alexis Giauque, Christophe Corre

Direct Numerical Simulations (DNS) of forced homogeneous isotropic turbulence in a dense gas (FC-70), accurately described by a complex EoS, are computed for a turbulent Mach number of 0.8. In a numerical experiment, results are compared to the ones obtained when considering the fluid as a perfect gas. It is found that the dense gas displays a deep...

A study of turbulence in BZT dense gas flows is performed using DNS. It is shown that for a large but realistic intensity, the turbulence in dense gas flows behaves in a highly compressible manner when the average thermodynamic state lies within the inversion region in which the gas fundamental derivative is negative. A close similarity is observed...

A study of turbulence in BZT dense gas flows is performed using DNS. It is shown that for a large but realistic intensity, the turbulence in dense gas flows behaves in a highly compressible manner when the average thermodynamic state lies within the inversion region in which the gas fundamental derivative is negative. A close similarity is observed...

When designing new propulsion systems, it can be very useful to quickly determine thermoacoustic transfer functions of the elements downstream of the combustion chamber, since they may play a key role in the onset and development of combustion instabilities. In order to reduce computational times, semi-analytical methods use quasi-1D flow assumptio...

The present paper deals with the generation of sound by the passage of acoustic or entropy perturbations through a nozzle in the nonlinear regime and in the low-frequency limit. The analytical model of Marble and Candel for compact nozzles (J. Sound Vib., vol. 55, 1977, pp. 225–243), initially developed for excitations in the linear regime, is rede...

Indirect combustion noise originates from the acceleration of nonuniform temperature or high vorticity regions when convected through a nozzle or a turbine. In a recent contribution (Giauque et al., 2012, “Analytical Analysis of Indirect Combustion Noise in Subcritical Nozzles,” ASME J. Eng. Gas Turbies Power, 134(11), p. 111202) the authors have p...

Indirect combustion noise originates from the acceleration of non-uniform temperature or high vorticity regions when convected through a nozzle or a turbine. In an recent contribution (Giauque et al., JEGTP, 2012), the authors have presented an analytical thermoacoustic model providing the indirect combustion noise generated by a subcritical nozzle...

This article revisits the problem of indirect combustion noise in nozzles of finite length. The analytical model proposed by Moase for indirect combustion noise is rederived and applied to subcritical nozzles having shapes of increasing complexity. This model is based on the equations formulated by Marble and Candel for which an explicit solution i...

This paper presents an analysis of the energy transported by disturbances in gaseous combustion. It extends the previous work of Myers (J. Fluid Mech., vol. 226, 1991, 383–400) and so includes non-zero mean-flow quantities, large-amplitude disturbances, varying specific heats and chemical non-equilibrium. This extended form of Myers’ ‘disturbance e...

This article revisits the problem of indirect combustion noise in nozzles of finite length. The analytical model proposed by Moase et al. (JFM 2007) for indirect combustion noise is rederived and applied to subcritical nozzles having shapes of increasing complexity. This model is based on the equations formulated by Marble & Candel (JSV 1977) for w...

Flame Transfer Functions (FTFs) are now an important ”brick” of acoustic analysis used for the design of complex turbulent combustors. Two different methods for the determination of FTFs in LES are compared. HF-FFT method, based on harmonic flame forcing and FFT post-processing is known to give results of global combustion delays that compare well wi...

Noise emissions from aircraft engines is an important problem, especially in the vicinity of airports. With innovative technologies such as double flux engines, jet noise has been drastically reduced during the past 20 years. Yet, with increasingly restrictive noise regulations, it is believed that further improvements will be obtained only through...

This paper presents an energy analysis of the disturbances that occur in gaseous com- bustion. The budgets of two fluctuating energies are considered. The first is the classical acoustic energy with its potential and kinetic contributions and the second includes entropy fluctuations. A numerical experiment, which corresponds to a ducted, laminar pr...

This paper presents a study of hot and cold turbulent jets by using the exact and linearised 'disturbance energy corollaries' proposed by Myers. Myers' energy corollaries are first extended to allow examination of results from Large Eddy Simulations (LES) around a turbulent base flow, via inclusion of additional disturbance energy flux and source t...

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 inclu...

Combustion noise is one of the main noise sources of aircraft auxiliary power unit gas turbine engines, and with the better understanding of jet and fan noise, combustion generated noise is also becoming increasingly important for the the main aircraft engines. Combustion generated noise comes from two major sources: direct noise, produced by the u...

The forced response of a swirled partially premixed burner to acoustic excitations is computed with Large Eddy Simulations and compared to measurements performed at University of Karlsruhe. The configuration is a 1:1 representation of a prototype industrial burner provided by Siemens in which gases are injected through two complex-geometry swirlers...

This paper presents an analysis of the energy transported by disturbances in gaseous combustion. It builds upon the previous work of Myers [J. Fluid Mech. 226 (1991) 383–400] by including species and heat release terms, thus extending Myers' exact and linearised 'energy corollaries' to gaseous combustion. These energy corollaries identify additiona...

L'objectif de cette thèse est d'étendre la compréhension des instabilités de combustion en testant des modèles, des concepts physiques, des méthodes numériques ainsi qu'en fournissant de nouveaux outils numériques pour y parvenir. Fonctions de transfert de flamme (FTF) : quatre méthodes numeriques de détermination de la FTF grâce à la Simulation au...