Imperial College London

DrSylvainLaizet

Faculty of EngineeringDepartment of Aeronautics

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 5045s.laizet Website

 
 
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Location

 

339City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

52 results found

Pinier B, Mémin E, Laizet S, Lewandowski Ret al., A stochastic flow approach to model the mean velocity profile of wall-bounded flows, Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), ISSN: 1539-3755

JOURNAL ARTICLE

Deskos G, Laizet S, Piggott MD, 2019, Turbulence-resolving simulations of wind turbine wakes, RENEWABLE ENERGY, Vol: 134, Pages: 989-1002, ISSN: 0960-1481

JOURNAL ARTICLE

Wu J-L, Sun R, Laizet S, Xiao Het al., 2019, Representation of stress tensor perturbations with application in machine-learning-assisted turbulence modeling, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, Vol: 346, Pages: 707-726, ISSN: 0045-7825

JOURNAL ARTICLE

Bartholomew P, Laizet S, 2019, A new highly scalable, high-order accurate framework for variable-density flows: Application to non-Boussinesq gravity currents, Computer Physics Communications, ISSN: 0010-4655

© 2019 Elsevier B.V. This paper introduces a new code “QuasIncompact3D” for solving the variable-density Navier–Stokes equations in the low-Mach number limit. It is derived from the Incompact3D framework which is designed for incompressible flows (Laizet and Lamballais, 2009). QuasIncompact3D is based on high-order accurate compact finite-differences (Lele, 1992), an efficient 2D domain decomposition (Laizet and Li, 2011) and a spectral Poisson solver. The first half of the paper focuses on introducing the low-Mach number governing equations, the numerical methods and the algorithm employed by QuasIncompact3D to solve them. Two approaches to forming the pressure-Poisson equation are presented: one based on an extrapolation that is efficient but limited to low density ratios and another one using an iterative approach suitable for higher density ratios. The scalability of QuasIncompact3D is demonstrated on several TIER-1/0 supercomputers using both approaches, showing good scaling up to 65k cores. Validations for incompressible and variable-density low-Mach number flows using the Taylor–Green vortex and a non-isothermal mixing layer, respectively, as test cases are then presented, followed by simulations of non-Boussinesq gravity currents in two- and three-dimensions. To the authors’ knowledge this is the first investigation of 3D non-Boussinesq gravity currents by means of Direct Numerical Simulation over a relatively long time evolution. It is found that 2D and 3D simulations of gravity currents show differences in the locations of the fronts, specifically that the fronts travel faster in three dimensions, but that it only becomes apparent after the initial stages. Our results also show that the difference in terms of front location decreases the further the flow is from Boussinesq conditions.

JOURNAL ARTICLE

Lamballais E, Dairay T, Laizet S, Vassilicos JCet al., 2019, Implicit/explicit spectral viscosity and large-scale SGS effects, ERCOFTAC Series, Pages: 107-113

© Springer Nature Switzerland AG 2019. In order to investigate the scale-selective influence of SGS on the large scale dynamics, DNS and LES are performed for the Taylor-Green vortex problem. An a priori analysis confirms the interest of the hyperviscous feature at small scale as used in implicit LES, SVV and VMS. However, the assumption of zero SGS dissipation at very large scales is found unrealistic for the high Reynolds number and coarse LES mesh considered. A posteriori analysis shows that SGS modelling based on the assumption of an inviscid cascade leads to a bottleneck effect on the kinetic energy spectrum with a significant underprediction of the total SGS dissipation. The simple addition of a constant eddy viscosity, even targeted to be optimal in terms of SGS dissipation, is unable to give realistic results. To allow accurate predictions by LES, a specific closure that incorporates both the hyperviscous feature (i.e. regularisation) and the expected SGS dissipation at large scales has to be developed.

BOOK CHAPTER

Margnat F, Ioannou V, Laizet S, 2018, A diagnostic tool for jet noise using a line-source approach and implicit large-eddy simulation data, COMPTES RENDUS MECANIQUE, Vol: 346, Pages: 903-918, ISSN: 1631-0721

JOURNAL ARTICLE

Schuch FN, Pinto LC, Silvestrini JH, Laizet Set al., 2018, Three-Dimensional Turbulence-Resolving Simulations of the Plunge Phenomenon in a Tilted Channel, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 123, Pages: 4820-4832, ISSN: 2169-9275

JOURNAL ARTICLE

Chandramouli P, Heitz D, Laizet S, Memin Eet al., 2018, Coarse large-eddy simulations in a transitional wake flow with flow models under location uncertainty, COMPUTERS & FLUIDS, Vol: 168, Pages: 170-189, ISSN: 0045-7930

JOURNAL ARTICLE

Ioannou V, Laizet S, 2018, Numerical investigation of plasma-controlled turbulent jets for mixing enhancement, International Journal of Heat and Fluid Flow, Vol: 70, Pages: 193-205, ISSN: 0142-727X

© 2018 The Authors Plasma-controlled turbulent jets are investigated by means of Implicit Large–Eddy Simulations at a Reynolds number equal to 460,000 (based on the diameter of the jet and the centreline velocity at the nozzle exit). Eight Dielectric Barrier Discharge (DBD) plasma actuators located just before the nozzle exit are used as an active control device with the aim to enhance the mixing of the jet. Four control configurations are presented in this numerical study as well as a reference case with no control and a tripping case where a random forcing is used to destabilize the nozzle boundary layer. Visualisations of the different cases and time-averaged statistics for the different controlled cases are showing strong modifications of the vortex structures downstream of the nozzle exit, with a substantial reduction of the potential core, an increase of the jet radial expansion and an improvement of the mixing properties of the flow.

JOURNAL ARTICLE

Dairay T, Lamballais E, Laizet S, Vassilicos JCet al., 2018, Physical scaling of numerical dissipation for LES, ERCOFTAC Series, Vol: 24, Pages: 149-155, ISSN: 1382-4309

In this work, we are interested in an alternative way to perform LES using a numerical substitute of a subgrid-scale model with a calibration based on physical inputs.

JOURNAL ARTICLE

Francisco EP, Espath LFR, Laizet S, Silvestrini JHet al., 2018, Reynolds number and settling velocity influence for finite-release particle-laden gravity currents in a basin, COMPUTERS & GEOSCIENCES, Vol: 110, Pages: 1-9, ISSN: 0098-3004

JOURNAL ARTICLE

Diaz-Daniel C, Laizet S, Vassilicos JC, 2017, Direct numerical simulations of a wall-attached cube immersed in laminar and turbulent boundary layers, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 68, Pages: 269-280, ISSN: 0142-727X

JOURNAL ARTICLE

Mahfoze O, Laizet S, 2017, Skin-friction drag reduction in a channel flow with streamwise-aligned plasma actuators, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 66, Pages: 83-94, ISSN: 0142-727X

JOURNAL ARTICLE

Dairay T, Lamballais E, Laizet S, Vassilicos JCet al., 2017, Numerical dissipation vs. subgrid-scale modelling for large eddy simulation, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 337, Pages: 252-274, ISSN: 0021-9991

JOURNAL ARTICLE

Diaz-Daniel C, Laizet S, Vassilicos JC, 2017, Wall shear stress fluctuations: Mixed scaling and their effects on velocity fluctuations in a turbulent boundary layer, PHYSICS OF FLUIDS, Vol: 29, ISSN: 1070-6631

JOURNAL ARTICLE

Benard N, Laizet S, Moreau E, 2017, PIV-based dynamic model of EHD volume force produced by a surface dielectric barrier discharge

© 2017 by N Benard. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. In this paper, an experimental measurement of the flow produced by a surface DBD plasma actuator has been conducted. One original aspect of these measurements by particle image velocimetry is the high acquisition rate for a PIV system (20 kHz). By using these highlyresolved flow measurements, the fluid flow velocity is used to estimate the spatial and temporal evolution of the EHD volume force. A reduced order model of this force has been constructed by proper orthogonal decomposition. Based on the analysis of the time-resolved expansion coefficients and their associated spatial modes, it is shown that the volume force can be reconstructed by using a limited number of POD modes (6 modes). This spatial and temporal filtering of the force fields remains faithful to the original data and it will help in view of an implementation of such a source term in a numerical solver. The resulting dynamic model shows an alternation of positive and negative volume forces. The strong positive EHD force developing during the glow regime of the DBD plasma discharge is visualized in a time-resolved manner. This positive force is immediately followed by a strong negative volume force probably caused by the local flow deceleration.

CONFERENCE PAPER

ahlfeld, laizet, Geraci G, Iaccarino G, Montomoli Fet al., 2016, Multi-Fidelity Uncertainty Quanti cation Using RANS and DNS, CTR Stanford Summer Program

CONFERENCE PAPER

Boschung J, Peters N, Laizet S, Vassilicos JCet al., 2016, Streamlines in stationary homogeneous isotropic turbulence and fractal-generated turbulence, FLUID DYNAMICS RESEARCH, Vol: 48, ISSN: 0169-5983

JOURNAL ARTICLE

Brauner T, Laizet S, Benard N, Moreau Eet al., 2016, Modelling of dielectric barrier discharge plasma actuators for direct numerical simulations

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. In recent years the development of devices known as plasma actuators has advanced the promise of controlling flows in new ways that increase lift, reduce drag and improve aerodynamic efficiencies; advances that may lead to safer, more efficient and quieter air­craft. The large number of parameters (location of the actuator, orientation, size, relative placement of the embedded and exposed electrodes, materials, applied voltage, frequency) affecting the performance of plasma actuators makes their development, testing and opti­misation a very complicated task. Several approaches have been proposed for developing numerical models for plasma actuators. The discharge can be modelled by physics-based kinetic methods based on first principles, by semi-empirical phenomenological approaches and by PIV-based methods where the discharge is replaced by a steady-state body force. The latter approach receives a recent interest for its easy implementation in RANS and U-RANS solvers. Here, a forcing term extracted from experiments is implemented into our high-order Navier-Stokes solver (DNS) in order to evaluate its robustness and ability to mimic the effects of a surface dielectric barrier discharge. This experimental forcing term is compared to the numerical forcing term developed by Suzen & Huang (1, 2) with an emphasis on the importance of the wall-normal component of each model.

CONFERENCE PAPER

Espath L, Francisco E, Moser C, Laizet S, Silvestrini Jet al., 2016, Particle-laden gravity currents in non-axisymmetric lock-exchange configurations, Second Conference on Forward Modelling of Sedimentary Systems, Pages: 110-114

� 2016, European Association of Geoscientists and Engineers, EAGE. All rights reserved. High-fidelity simulations of particle-laden gravity currents in non-axisymmetric lock-exchange configurations are presented and compared with more conventional channelized and axysymmetric lock-exchange configurations. We limit our investigations to gravity currents over a flat bed in which density differences are small enough for the Boussinesq approximation to be valid. The concentration of particles is described in an Eulerian fashion by using a transport equation combined with the incompressible Navier-Stokes equations. Our non-axisymmetric results highlight similarities and differences with axisymmetric and channelized lock-exchange configurations and show that the dynamics of the current and final deposition maps are significantly influenced by the geometry of the initial reservoir.

CONFERENCE PAPER

Laizet S, Nedic J, Vassilicos JC, 2015, The spatial origin of-5/3 spectra in grid-generated turbulence, Physics of Fluids, Vol: 27, ISSN: 1089-7666

A combined wind tunnel and computational study of grid-generated turbulencealong the centreline shows that the close to −5/3 power law signature of energyspectra in the frequency domain originates relatively close to the grid not only wherethe velocity derivative statistics become quite suddenly isotropic but also wherethe turbulent fluctuating velocities are very intermittent and non-Gaussian. As theinlet flow velocity increases, these power laws are increasingly well defined andincreasingly close to −5/3 over an increasing range of frequencies. However, thisrange continuously decreases with streamwise distance from the grid even though thelocal Reynolds number first increases and then decreases along the same streamwiseextent. The intermittency at the point of origin of the close to −5/3 power spectraconsists of alternations between intense vortex tube clusters with shallow broad-bandspectra and quiescent regions where the velocity fluctuations are smooth with steepenergy spectra.

JOURNAL ARTICLE

Espath LFR, Pinto LC, Laizet S, Silvestrini JHet al., 2015, High-fidelity simulations of the lobe-and-cleft structures and the deposition map in particle-driven gravity currents, Physics of Fluids, Vol: 27, Pages: 056604-056604, ISSN: 1089-7666

The evolution of a mono-disperse gravity current in the lock-exchange configurationis investigated by means of direct numerical simulations for various Reynoldsnumbers and settling velocities for the deposition. We limit our investigations togravity currents over a flat bed in which density differences are small enough for theBoussinesq approximation to be valid. The concentration of particles is described inan Eulerian fashion by using a transport equation combined with the incompressibleNavier-Stokes equations. The most interesting results can be summarized asfollows: (i) the settling velocity is affecting the streamwise vortices at the head ofthe current with a substantial reduction of their size when the settling velocity isincreased; (ii) when the Reynolds number is increased the lobe-and-cleft structuresare merging more frequently and earlier in time, suggesting a strong Reynoldsnumber dependence for the spatio-temporal evolution of the head of the current;(iii) the temporal imprint of the lobe-and-cleft structures can be recovered fromthe deposition map, suggesting that the deposition pattern is defined purely andexclusively by the structures at the front of the current.

JOURNAL ARTICLE

Laizet S, Nedic J, Vassilicos C, 2015, Influence of the spatial resolution on fine-scale features in DNS of turbulence generated by a single square grid, INTERNATIONAL JOURNAL OF COMPUTATIONAL FLUID DYNAMICS, Vol: 29, Pages: 286-302, ISSN: 1061-8562

JOURNAL ARTICLE

Laizet S, Vassilicos JC, 2015, Stirring and scalar transfer by grid-generated turbulence in the presence of a mean scalar gradient, JOURNAL OF FLUID MECHANICS, Vol: 764, Pages: 52-75, ISSN: 0022-1120

JOURNAL ARTICLE

Gautier R, Laizet S, Lamballais E, 2014, A DNS study of jet control with microjets using an immersed boundary method, INTERNATIONAL JOURNAL OF COMPUTATIONAL FLUID DYNAMICS, Vol: 28, Pages: 393-410, ISSN: 1061-8562

JOURNAL ARTICLE

Espath LFR, Pinto LC, Laizet S, Silvestrini JHet al., 2014, Two- and three-dimensional Direct Numerical Simulation of particle-laden gravity currents, COMPUTERS & GEOSCIENCES, Vol: 63, Pages: 9-16, ISSN: 0098-3004

JOURNAL ARTICLE

Laizet S, Vassilicos JC, Cambon C, 2013, Interscale energy transfer in decaying turbulence and vorticity-strain-rate dynamics in grid-generated turbulence, FLUID DYNAMICS RESEARCH, Vol: 45, ISSN: 0169-5983

JOURNAL ARTICLE

Baggaley AW, Laizet S, 2013, Vortex line density in counterflowing He II with laminar and turbulent normal fluid velocity profiles, PHYSICS OF FLUIDS, Vol: 25, ISSN: 1070-6631

JOURNAL ARTICLE

Laizet S, Christos Vassilicos J, 2013, Stirring and mixing by grid-generated turbulence in the presence of a mean scalar gradient

The stirring and mixing of a passive scalar by gridgenerated turbulence in the presence of a mean scalar gradient is studied in three dimensions by DNS (Direct Numerical Simulation). Using top-end high fidelity computer simulations, we calculate and compare the effects of various fractal and regular grids on scalar transfer and turbulent diffusion efficiencies. We demonstrate the existence of a new mechanism present in turbulent flows generated by multiscale/fractal objects which has its origin in the multiscale/ fractal space-scale structure of such turbulent flow generators. As a result of this space-scale unfolding (SSU) mechanism, fractal grids can enhance scalar transfer and turbulent diffusion by one order of magnitude while at the same time reduce pressure drop by half. The presence of this SSU mechanism when turbulence is generated by fractal grids means that the spatial distribution of length-scales unfolds onto the streamwise extent of the flow and gives rise to a variety of wake-meeting distances downstream. This SSU mechanism must be playing a decisive role in environmental, atmospheric, ocean and river transport processes wherever turbulence originates from multiscale/fractal objects such as trees, forests, mountains, rocky river beds and coral reefs. It also ushers in the new concept of fractal design of turbulence which may hold the power of setting entirely new mixing and cooling industrial standards.

CONFERENCE PAPER

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