Ecole Centrale Research Articles

Pierre J. Y. Hubert (1943–2020)

Pierre Hubert (1943–2020) passed away on 31st December 2020. He graduated with a degree in engineering from the Ecole Centrale in Paris in 1967, and was awarded his PhD in 1971 and his Habilitation...

Simulations of helicopter ditching using smoothed particle hydrodynamics

The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters (SARAH) dedicated to improving the safety during aircraft ditching, together with a better understanding of the physics involved during those crucial events. Both numerical and experimental aspects are explored during this project. The present study focuses on the application of the smoothed particle hydrodynamics (SPH) method to the simulation of helicopter ditching, as this method has proved to be particularly adapted to free surface impact cases. Simulations are performed for three different impact configurations, for which the numerical solutions are compared with the experimental results (forces and kinematics) obtained at the wave basin of Ecole Centrale Nantes on a mock-up shape provided by Airbus Helicopters. Elements of sensitivity analysis are also provided when needed, to assess the role of some parameters involved in the helicopter behavior and the fluid pressure forces exerted during the impact.

Corner Stall Prediction in a Compressor Linear Cascade Using Very Large Eddy Simulation Lattice-Boltzmann Method

AbstractCompressor corner stall is a phenomenon difficult to predict with numerical tools but essential to the design of axial compressors. Predictive methods are beneficial early in the design process to understand design and off-design limitations. Prior numerical work using Navier–Stokes computational methods has assessed the prediction capability for corner stall. Reynolds-averaged Navier–Stokes (RANS) simulations using several turbulence models have shown to over-predict the region of corner hub stall where large eddy simulations (LES) and detached eddy simulations (DES) approaches improved the airfoil surface and wake pressure loss prediction. A linear compressor cascade designed and tested at Ecole Centrale de Lyon provides a good benchmark for the evaluation of the accuracy of numerical methods for corner stall. This paper presents results obtained with Lattice-Boltzmann method (LBM) coupled with very large-eddy simulations (VLES) approach of PowerFLOW and compares them with the experimental and numerical work from Ecole Centrale de Lyon. The ability to achieve equivalent accuracy at a lower computational cost compared to LES scale resolving methods can enable multi-stage design and off-design compressor predictions. A methodical approach is taken by first accurately simulating the upstream flow conditions. Geometric trips are modeled upstream on the endwalls to match both the mean and fluctuating inflow boundary layer conditions. These conditions were then applied to the simulation of the linear compressor cascade. The benchline experimental study includes trips on both the pressure and suction of the airfoil. These trips are also included for the current simulation. The significance of capturing both inflow conditions and including trips on the airfoil is assessed. Detailed comparisons are then made to airfoil loading and downstream losses between experiment and previous RANS and LES simulations. LBM-VLES corner stall results of pitchwise averaged total pressure match LES agreement relative to experimental data at 50 times lower computational cost.

Transient vibro-acoustic analysis of squeal events based on the experimental bench FIVE@ECL

The proposed study investigates the transient and stationary non-linear vibrations and acoustic phenomena occurring during the squeal phenomenon. Experiments are performed on the test bench Friction-Induced Vibration and noisE at Ecole Centrale de Lyon (FIVE@ECL).The first major contribution of the study is to demonstrate the ability of this test bench to reproduce transient squeal events for a given operational condition, allowing to conduct a thorough and robust study on the physical understanding of transient vibration and acoustic squeal events. The second main contribution is to discuss the potential links between the emergence of vibrations on the two pads, the disc and the caliper, and the squeal noise in near-field and far-field.

Numerical Modeling of Interply Adhesion in Composite Forming of Viscous Discontinuous Thermoplastic Prepregs

“Quilted Stratum Process” (QSP®) is a new process developed by CETIM, Ecole Centrale de Nantes and their partners which is in the category of thermoplastic composite forming. Unlike the conventional thermoforming process, a QSP® preform stack consists of several discontinuous plies. Due to the inability of using the blank-holders in this process, these discontinuous patches can experience large sliding and/or rotation. Thus, the mechanisms occurring at ply-ply interfaces, especially the interply adhesion are important and should be considered in the process simulation. A penalty based, semi-empirical contact model is proposed and implemented in the industrial code of Altair RADIOSSTM in order to model interply adhesion. This model allows sliding of plies over long distance while providing a finite adhesive strength before delamination and it has resulted in a significant improvement in the prediction of the final positions and orientation of the discontinuous patches in QSP® simulation. The model requires minimal characterization making it suitable for industrial applications.

Extended-reacting liners in time-domain simulations for broadband attenuation with flow

The modeling and optimization of acoustic liners under grazing flow is an on-going research topic with applications in the aerospace, automotive and railway industries. Recently, the push for next generation airliners and low-noise ventilation systems further increase the need for innovative configurations with improved broadband performance, and with limited size. Porous materials and metamaterials are good candidates to achieve these goals. In this work we propose a time-domain numerical modeling of extended reacting liners using an effective medium approach, which allows to characterize complex media such as porous materials and metamaterials through their effective density and compressibility. The linearized Euler equations are solved in the time domain using efficient high-order finite-difference schemes. The calculation of the convolution integrals is avoided through the auxiliary differential equation method. After a validation of the numerical methodology in a 1-D case, we will present the results for various 2-D configurations, with special attention to the impact of flow. A number of experiments in a Kundt’s tube and in a wind tunnel at the Ecole Centrale de Lyon are also under way to test the model predictions.

Comparison of wave modeling methods in CFD solvers for ocean engineering applications

Numerical wave tanks rely on specific models to generate realistic wave condition, propagate accurately the waves in the domain, and absorb the reflected waves at the boundaries. In this paper, three wave modeling methods for two-phase CFD solvers are compared, including the Internal Wave Generator method, the Relaxation Zone method, and the Spectral Wave Explicit Navier Stokes Equations (SWENSE) method. The first two methods consist in generating and absorbing the waves in specific regions of the domain, while the third achieves a potential/viscous coupling in the entire domain. These methods, implemented either in OpenFOAM or in ISIS-CFD are compared by simulating a fixed Catenary Anchor Leg Mooring (CALM) buoy in regular waves. The simulation results are compared with available experimental data obtained by a model test in the Ocean Engineering Tank of Ecole Centrale de Nantes. The comparison shows the efficiency and the accuracy of these waves modeling methods. A problem related to the turbulence modeling in two-phase flow is also remarked.

Squeal analysis based on the laboratory experimental bench “Friction-Induced Vibration and noisE at École Centrale de Lyon” (FIVE@ECL)

Abstract This paper presents a new experimental test bench, called Friction-Induced Vibration and noisE at Ecole Centrale de Lyon (FIVE@ECL). This experimental bench aims at discussing some of the open issues in understanding squealing disc brakes. Measurements for friction-induced vibration and squeal noise are performed to investigate the dynamic behavior of the system under study and its squeal characterization through experiments. One of the main original contributions is to share the data sets to give the opportunity to researchers for conducting new analysis and testing numerical models of brake system with the proposed data of squeal noise. The data provided include all the measurements on the two pads, the caliper and the disc, as well as the measurement of pressure in near-field and in far-field.

Hybrid RANS/LES Simulation of Corner Stall in a Linear Compressor Cascade

Current design-cycle Reynolds-averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) methods have the tendency to over-predict corner-stall events for axial-flow compressors operating at off-design conditions. This shortcoming has been demonstrated even in simple single-row cascade configurations. Here we report on the application of hybrid RANS/large eddy simulation (LES), or detached eddy simulation (DES), for simulating the corner-stall data from the linear compressor cascade work conducted at Ecole Centrale de Lyon. This benchmark data set provides detailed loss information while also revealing a bimodal behavior of the separation which, not surprisingly, is also not well modeled by RANS. The hybrid RANS/LES results presented here predict bimodal behavior similar to the data only when special treatment is adopted to resolve the leading-edge endwall region where the horseshoe vortex (HV) forms. The (HV) is shown to be unstable, which produces the bimodal instability. The DES simulation without special treatment or refinement in the HV region fails to predict the bimodal instability, and thus the bimodal behavior of the separation. This, in turn, causes a gross over-prediction in the scale of the corner-stall. The HV region is found to be unstable with rolling of the tertiary vortex (TV) over the secondary vortex and merging with the primary HV. With these flow dynamics realized in the DES simulations, the corner stall characteristics are found to be in better agreement with the experimental data, as compared to RANS and standard DES approaches.

Experimental investigation of the turbulent density – Far-field sound correlations in compressible jets

Jet mixing noise is experimentally investigated by means of cross-correlations between density fluctuations inside the turbulent jet flow and the far-field acoustic pressure. The time-resolved density fluctuations are measured by an experimental device based on Rayleigh scattering, which is mounted in the large anechoic wind tunnel of Ecole Centrale de Lyon. An original signal processing developed in a previous study is implemented for the photon counting, combined with the use of a single photomultiplier to remove shot noise. A high-speed subsonic jet and a perfectly expanded supersonic jet with a subsonic convective velocity are considered to characterize mixing noise sources. In order to go beyond the classical Fourier analyses, conditional cross-correlations are determined, and the signature of turbulent events linked to the noise emission in the downstream direction is extracted.

Engineer and Builder: Gustave Eiffel—Master of Iron Construction (1832–1923)

1832Born on 15 December in Dijon, France1855Graduates with a degree in Civil Engineering from the Ecole Centrale des Arts et Manufactures, now known as the Ecole Centrale Paris1858Supervises the co...

High-order delay detached-eddy simulations of cylindrical separated vortex/vortex induced noise based on transition model and acoustic analogy

The numerical prediction of transition from laminar to turbulent flow has proven to be an arduous challenge to computational fluid dynamics (CFD). Few approaches can provide routine accurate results within the cost limitations of engineering applications. In the present paper described is the application of a -Re transition model in combination with the delay detached eddy simulation (DDES) and Ffowcs Williams and Hawkings (FW-H) acoustic analogy method to cylinder vortex/vortex induced noise at a subcritical Reynolds number. In the process of numerical simulation, a traditional DDES based on the full-turbulence model SST is carried out for comparison and a 7th-order weighted compact nonlinear scheme (WCNS-E8T7) is adopted to ensure that the physical models are not affected by numerical dissipation or dispersion. In the first case, single cylinder cross-flow at ReD =4.3104 and Ma=0.21, is considered as a benchmarking problem for validating turbulence models and aerodynamic noise prediction methods. Its aerodynamic coefficients, St, CL and CD at root-mean-square (rms) and averaged values are measured by Szepessy and Bearman, while an acoustic measurement was recently made at Ecole Centrale de Lyon. The traditional DDES only based on SST model (SST-DDES) delays the instability of the shear layer on the sides of the cylinder, which leads to the recirculation zone in mean flow to grow and the induced drag to increase. Moreover, the vortex shedding frequency predicted by SST-DDES is larger than the actual value, which makes the whole sound pressure level (SPL) spectrum move toward high frequency region. However, combining the -Re transition model, the DDES (called Tran-DDES in the present article) can give the results in good agreement with the experimental data. In the second case considered is an airfoil in the wake of the cylinder. The flow condition is similar to that in the first case and the experimental results are also obtained at Ecole Centrale de Lyon. The issue of SST-DDES in recirculation zone in mean flow is weakened, which relates to the interaction between the airfoil and cylinder wake, the prediction of mean flow by SST-DDES is similar to that by the Tran-DDES. But in terms of the rms values of turbulent fluctuation components and SPL, the predictions by Tran-DDES are still better than those by SST-DDES.

Evaluation of wire arc additive manufacturing for large-sized components in naval applications

By extrapolating knowledge in multipass welding and developing multiaxial robot solutions, the wire deposit in 3D or wire arc additive manufacturing (WAAM) can be an innovative solution to propose a credible alternative for rough cast parts with a large size and a quite complex geometry such as different components for naval application. In the framework of the Joint Laboratory of Marine Technology (JLMT), DCNS Research and Ecole Centrale de Nantes (ECN) are associated to develop especially additive manufacturing activities for large components. In this experimental study, the authors propose to investigate for two different metallic materials the conditions of the filler material deposit by the CMT® process and the consequences on the manufacturing time. Moreover, the in-service performance (mechanical and corrosion properties) is evaluated. In a first approach, austenitic stainless steel and copper-aluminum alloys have been evaluated.

A linear numerical model for analysing the hydroelastic response of a flexible electroactive wave energy converter

In this paper, a linear mathematical and numerical model for analysing the dynamic response of a flexible electroactive wave energy converter is described. The Wave Energy Converter (WEC) is a floating elastic tube filled with slightly pressurised sea water. It is made of Electroactive Polymers (EAPs). Under simplifying assumptions, a set of governing equations is formulated for the flow inside the tube, the flow outside the tube and the behaviour of the tube wall. By combining them, the evolution of the flow velocity in the tube can be written as a wave equation. The corresponding eigenmodes of vibration are calculated. Then, using spectral decomposition, the equation of motion for the response of the tube in waves is derived. Experiments were carried out on a scale model of the wave energy converter in the wave tank of Ecole Centrale de Nantes in 2011. Numerical results are compared with experimental results in regular waves, showing rather good agreement, which validates the model and the initial modelling assumptions. Finally, estimates are made for the energy performance of a possible prototype.

Observations on Rotating Instabilities and Spike Type Stall Inception in a High-Speed Multistage Compressor

This work investigates high-frequency measurements for the contribution to the understanding of different stall inception types in high-speed multistage compressors. A 3.5-stage high-speed axial multistage compressor is investigated with a 2 MW test rig in the Laboratoire de Mécanique des Fluides et d’Acoustique (LMFA) at Ecole Centrale de Lyon, France. Two different types of instabilities arise in this compressor as a function of shaft speed. At part speed, a controversy called “rotating instability” type flow field modulation is identified with the measurements. New results are the demonstration of the periodic behavior of this instability and the analogy to classical frequency modulation, periodic to one revolution of the instability. Furthermore, the amplitude of the instability is modulated by the time period of a rotor revolution. At nominal speed, the abrupt spike type stall inception is detected, taking usually less than five rotor revolutions.

Comparison of Experiments and CFD Simulations of a Braceless Concrete Semi-submersible Platform

A braceless concrete substructure for floating offshore wind turbines was designed and analysed in 2014 by Dr.tech. Olav Olsen AS,IFE and Acciona within an industrial project co-financed by the Research Council in Norway. A simplified model of the structure in scale 1:40 was tested in 2014 at the Hydrodynamic and Ocean Engineering tank at Ecole Centrale de Nantes (ECN) by IFE and CENER.A number of tests including regular and irregular waves for free and fixed hull, and decay tests were carried out. The present paper shows a comparison between experiments and CFD simulation for free decay tests in heave, and surge motion and test in regular waves for fixed and free hull.The commercial CFD solver STARCCM+ was used for the CFD simulations. A numerical wave tank was modelled with using a trimmed mesh with surface refinement. The surface refinement was varied depending on the wave length and height in order to ensure at least 20 cells per wave height and 100 cells per wave length. The time step was chosen in order to ensure a Courant number around 0.5. A volume of fluid method was used and the k-ω turbulence model was used to solve the turbulent part of the averaged Navier-Stokes equations. For the free hull cases the overset meshing technique with the DFBI model included in StarCCM+ was used. The mooring lines were simplified and equivalent elastic springs were used instead of the catenary system used in the experiments. The results show a good comparison between the experiments and the CFD simulations for both regular waves and decay tests.

Adaptive Mesh Refinement and High Order Geometrical Moment Method for the Simulation of Polydisperse Evaporating Sprays

Predictive simulation of liquid fuel injection in automotive engines has become a major challenge for science and applications. The key issue in order to properly predict various combustion regimes and pollutant formation is to accurately describe the interaction between the carrier gaseous phase and the polydisperse evaporating spray produced through atomization. For this purpose, we rely on the EMSM (Eulerian Multi-Size Moment) Eulerian polydisperse model. It is based on a high order moment method in size, with a maximization of entropy technique in order to provide a smooth reconstruction of the distribution, derived from a Williams-Boltzmann mesoscopic model under the monokinetic assumption [O. Emre (2014) PhD Thesis , Ecole Centrale Paris; O. Emre, R.O. Fox, M. Massot, S. Chaisemartin, S. Jay, F. Laurent (2014) Flow, Turbulence and Combustion 93 , 689-722; O. Emre, D. Kah, S. Jay, Q.-H. Tran, A. Velghe, S. de Chaisemartin, F. Laurent, M. Massot (2015) Atomization Sprays 25 , 189-254; D. Kah, F. Laurent, M. Massot, S. Jay (2012) J. Comput. Phys. 231 , 394-422; D. Kah, O. Emre, Q.-H. Tran, S. de Chaisemartin, S. Jay, F. Laurent, M. Massot (2015) Int. J. Multiphase Flows 71 , 38-65; A. Vie, F. Laurent, M. Massot (2013) J. Comp. Phys. 237 , 277-310]. The present contribution relies on a major extension of this model [M. Essadki, S. de Chaisemartin, F. Laurent, A. Larat, M. Massot (2016) Submitted to SIAM J. Appl. Math.], with the aim of building a unified approach and coupling with a separated phases model describing the dynamics and atomization of the interface near the injector. The novelty is to be found in terms of modeling, numerical schemes and implementation. A new high order moment approach is introduced using fractional moments in surface, which can be related to geometrical quantities of the gas-liquid interface. We also provide a novel algorithm for an accurate resolution of the evaporation. Adaptive mesh refinement properly scaling on massively parallel architectures yields a precise integration of transport in physical space limiting both numerical dissipation as well as the memory trace of the solver. A series of test-cases is presented and analyzed, thus assessing the proposed approach and its parallel computational efficiency while evaluating its potential for complex applications.

Professor Abderrahmane Beroual, Ecole Centrale de Lyon AMPERE laboratory, recipient of the DEIS 2016 T. W. Dakin Distinguished Technical Contributions Award

Professor Abderrahmane Beroual, Ecole Centrale de Lyon AMPERE laboratory, recipient of the DEIS 2016 T. W. Dakin Distinguished Technical Contributions Award

Challenging modeling strategies for LES of non-adiabatic turbulent stratified combustion

Five different low-Mach large eddy simulations are compared to the turbulent stratified flame experiments conducted at the Technical University of Darmstadt (TUD). The simulations were contributed by TUD, the Institute for Combustion Technology (ITV) at Aachen, Lund University (LUND), the EM2C laboratory at Ecole Centrale Paris, and the University of Duisburg-Essen (UDE). Combustion is modeled by a premixed flamelet tabulation with local flame thickening (TUD), a premixed flamelet progress variable approach coupled to a level set method (ITV), a 4-steps mechanism combined with implicit LES (LUND), the F-TACLES model that is based on filtered premixed flamelet tabulation (EM2C), and a flame surface density approach (UDE). An extensive comparison of simulation and experimental data is presented for the first two moments of velocity, temperature, mixture fraction, and major species mass fractions. The importance of heat-losses was assessed by comparing simulations for adiabatic and isothermal boundary conditions at the burner walls. The adiabatic computations predict a flame anchored on the burner lip, while the non-adiabatic simulations show a flame lift-off of one half pilot diameter and a better agreement with experimental evidence for temperature and species concentrations. Most simulations agree on the mean flame brush position, but it is evident that subgrid turbulence must be considered to achieve the correct turbulent flame speed. Qualitative comparisons of instantaneous snapshots of the flame show differences in the size of the resolved flame wrinkling patterns. These differences are (a) caused by the influence of the LES combustion model on the flame dynamics and (b) by the different simulation strategies in terms of grid, inlet condition and numerics. The simulations were conducted with approaches optimized for different objectives, for example low computational cost, or in another case, short turn around.

Jean‐Marie Georges

It is with great sadness we announce the passing of Professor Jean-Marie Georges on Wednesday the 28th of January 2015. Jean-Marie was born in Chaumont (Haute-Marne) in 1939 and studied at the Ecole Centrale de Lyon, where he obtained his doctorate in 1964. His scientific career started in the French engineering industry at the Center for Hydromécanique et Frottement in Saint-Étienne, where he studied electrochemical surface treatments to reduce surface wear, which was also the subject of his PhD thesis. In 1968 Professor Georges left France to continue his research work at the Massachusetts Institute of Technology. On his return to France Professor Georges took up an Academic appointment at the Ecole Centrale de Lyon and in 1970 established the Département de Technologie des Surfaces. In 1992, the laboratory was enlarged and renamed the Laboratoire de Tribologie et Dynamique des Systemes (LTDS). The laboratory is now recognised as one of the leading tribology research groups world-wide. Throughout his career, he also maintained close international relations, especially with Japan and the University of Tohoku in Sendai. Professor Georges’ research focused on understanding tribology mechanisms at the nanometer scale. To do this he and his group designed and developed highly-sensitive equipment capable of measuring and understanding lubricating film properties at the molecular level. These new capabilities initiated the study of boundary films, molecular friction, surface rheology and lubricant additive mechanisms. Professor Georges is particularly known for his work on zinc dialkyl dithiophosphates which are an important class of lubricant antiwear additives. The research was reported in many significant papers published in international journals. One outstanding aspect of his work was the ability to communicate his research to a wider audience and to place the findings in an engineering context. The work did not exist in an academic vacuum but contributed to the benefit of industry and society. For this reason Professor Georges participated in the program “la main à la pâte”, teaching at a secondary school, generating giant soap bubbles to the delight of the schoolchildren and their teachers. His studies are summarized in his book published in 2000: Frottement, usure et lubrification: La tribologie ou science des surfaces. During his career Professor Georges received many national and international awards recognising the importance of his work. In 1993, he was elected senior member of the Institut Universitaire de France (IUF). Professor Georges also received the 1994 Tribology Trust Gold Medal from the Institution of Mechanical Engineers UK which is awarded each year to outstanding Tribologists on the world stage. The citation states the award is “In recognition of his outstanding contribution to tribology and in particular, to the development of techniques for the measurement and analysis of surface forces on the molecular or nanometric scale”. Professor Georges was a great scientist, respected and admired by all, at ease amidst tribologists and physicists in France and worldwide. We are indebted to him and remember him as a great man, a great teacher, with an unlimited curiosity, a communicative enthusiasm, grand gestures and an unforgettable laugh. We will miss Jean-Marie immensely and offer our deepest condolences to his family.