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October 2015 - December 2022

September 2014 - present

January 2007 - August 2014

## Publications

Publications (519)

Thermal-hydraulics safety requirements for the second and third generation of nuclear reactors led to the development of innovative passive safety systems. In particular, new devices must be developed involving numerical simulations for turbulent two-phase flows around complex geometries. To reduce the time-consuming mesh generation phase when test...

This paper applies a recently developed immersed boundary-turbulence wall modeling approach to turbulent flows over a generic car geometry, known as the Ahmed body, under massive flow separation, within a lattice Boltzmann solver. Although the immersed boundary method combined with hierarchical Cartesian grid offers high flexibility in automatic gr...

Resolvent analysis is used to study the low-frequency behaviour of the laminar oblique shock wave/boundary layer interaction (SWBLI). It is shown that the computed optimal gain, which can be seen as a transfer function of the system, follows a first-order low-pass filter equation, recovering the results of Touber & Sandham ( J. Fluid Mech. , vol. 6...

View Video Presentation: https://doi.org/10.2514/6.2022-3687.vid The arrival of the new generation of aircrafts, complexifies engine integration. In this context assessing engine integration early in the design phase of a new aircraft is essential, saving development times, and reducing cost and uncertainties, as well as enhancing the aircraft’s pe...

Mass leakage at boundaries can be a critical issue for the reliability of the lattice Boltzmann (LB) method based on Cartesian grids. Despite numerous works based on the LB method, the intrinsic macroscopic mechanisms causing mass leakage are still not fully characterized but are essential to improve the mass conservation of LB simulations. In this...

A compressible Hybrid Lattice Boltzmann Method solver is used to perform a wall-resolved Large eddy simulation of an isothermal axisymmetric jet issuing from a pipe and impinging on a heated flat plate at a Reynolds number of 23 000, a Mach number of 0.1, and an impingement distance of two jet diameters. The jet flow field statistics, Nusselt numbe...

Resolvent analysis is used to study the low-frequency behaviour of the laminar oblique shock wave / boundary layer interaction (SWBLI). It is shown that the computed optimal gain, which can be seen as a transfer function of the system, follows a first-order low-pass filter equation, recovering the results of Touber and Sandham (JFM, 2011). This beh...

A new low-Mach algorithm based on thermal Lattice Boltzmann method (LBM) is proposed aiming at reducing the computational cost of thermal flow simulations in low Mach number limit.Considering the time-step restriction of fully compressible solvers, the Low Mach Number Approximation (LMNA) allows to accelerate significantly the simulations by re-sca...

A general methodology is introduced to build conservative numerical models for fluid simulations based on segregated schemes, where mass, momentum and energy equations are solved by different methods. It is here especially designed for developing new numerical discretizations of the total energy equation, adapted to a thermal coupling with the latt...

A D3Q19 Hybrid Recursive Regularized Pressure based Lattice Boltzmann Method (HRR-P LBM) is assessed for the simulation of complex transonic flows. Mass and momentum conservation equations are resolved through a classical LBM solver coupled with a finite volume resolution of entropy equation for a complete compressible solver preserving stability,...

This paper addresses simulation of heat dominated compressible flows in a closed cavity using a pressure-based lattice Boltzmann (LB) method, in which thermal effects are modeled by applying a pressure-featured zero-order moment of distribution functions. A focus is made on the conservation of mass at boundary nodes, which is a challenging issue th...

With the aim of better understanding the numerical properties of the lattice Boltzmann method (LBM), a general methodology is proposed to derive its hydrodynamic limits in the discrete setting. It relies on a Taylor expansion in the limit of low Knudsen numbers. With a single asymptotic analysis, two kinds of deviations with the Navier-Stokes (NS)...

In the framework of the development of new passive safety systems for the second and third generations of nuclear reactors, the numerical simulations, involving complex turbulent two-phase flows around thin or massive inflow obstacles, are privileged tools to model, optimize and assess new design shapes. In order to match industrial demands, comput...

An immersed boundary method is coupled to a turbulent wall model and Large Eddy Simulation, within the Lattice-Boltzmann framework. The method is able to handle arbitrarily moving objects immersed in a high Reynolds number flow and to accurately capture the shear layer and near wall effects. We perform a thorough numerical study which validates the...

The present study proposes an accurate lattice Boltzmann direct coupling algorithm, well suited for industrial purposes, making it highly valuable for aeroacoustic applications. It is indeed known that the convection of vortical structures across a grid refinement interface, where cell size is abruptly doubled, is likely to generate spurious noise...

In closed rooms with limited convection human motion can considerably affect the airflow and thus the dispersion of pollutant. However, in Computational Fluid Dynamics (CFD) simulations on air quality and safety for human beings this effect is generally not considered, which is mainly due to a lack of a well-founded and detailed estimation of the h...

An original spectral study of the compressible hybrid lattice Boltzmann method (HLBM) on standard lattice is proposed. In this framework, the mass and momentum equations are addressed using the lattice Boltzmann method (LBM), while finite difference (FD) schemes solve an energy equation. Both systems are coupled with each other thanks to an ideal g...

A unified expression for high-speed compressible segregated consistent lattice Boltzmann methods, namely pressure-based and improved density-based methods, is given. It is theoretically proved that in the absence of forcing terms these approaches are strictly identical and can be recast in a unique form. An important result is that the difference w...

Mesocale atmospheric flows that develop in the boundary layer or microscale flows that develop in urban areas are challenging to predict, especially due to multiscale interactions, multiphysical couplings, land and urban surface thermal and geometrical properties and turbulence. However, these different flows can indirectly and directly affect the...

The article deals with an improved treatment of wall models for the simulation of turbulent flows in the framework of Immersed Wall Boundaries on Cartesian grids. The emphasis is put on the implementation in a Lattice-Boltzmann Method solver without loss of generality, since the proposed approach can be used in Navier-Stokes-based solvers in a stra...

Simulating rotating geometries in fluid flows for industrial applications remains a challenging task for general fluid solvers and in particular for the lattice Boltzmann method (LBM) due to inherent stability and accuracy problems. This work proposes an original method based on the widely used overset grids (or Chimera grids) while being integrate...

A Lattice-Boltzmann-based Large-Eddy Simulation approach for wind load prediction on high-rise building is proposed and validated. An extension of the original incompressible Synthetic Eddy Method to reconstruct inlet turbulence is proposed within the Lattice-Boltzmann framework, including a low-noise frozen density variant. Extensive successful co...

We propose a new direct coupling scheme based on the overset technique to tackle moving boundary problems within the lattice Boltzmann framework. The scheme is based on the interpolation of distribution functions rather than moments, that is, macroscopic variables, and includes an additional hypothesis ensuring mass and momentum conservation at the...

With the aim of better understanding the numerical properties of the lattice Boltzmann method (LBM), a general methodology is proposed to derive its hydrodynamic limits in the discrete setting. It relies on a Taylor expansion in the limit of low Knudsen numbers. With a single asymptotic analysis, two kinds of deviations with the Navier-Stokes (NS)...

Turbulence is a common feature to all flows that surround us. Despite its ubiquity, particularly in industrial flows, it is very difficult to provide a mathematical framework for the generation of turbulent eddies. Several methods have been proposed which are able to reproduce realistic features for velocity fluctuations, exhibiting proper space- a...

Algebraic explicit wall models covering the entire inner region of the turbulent boundary layer are proposed to reduce the computational effort for large eddy simulation of wall-bounded turbulent flows. The proposed formulas are given in closed forms with either logarithmic- or power-function-based laws of the wall, allowing straightforward evaluat...

Abstract A large‐eddy simulation tool is developed for simulating the dynamics of atmospheric boundary layers (ABLs) using lattice Boltzmann method (LBM), which is an alternative approach for computational fluid dynamics and proved to be very well suited for the simulation of low‐Mach flows. The equations of motion are coupled with the global compl...

Lattice Boltzmann (LB) method for atmospheric dynamics is developed by considering the characteristics of the anelastic approximation. After introducing reference base state values in atmospheric flows, an LB model, with an external force term, has been constructed in anelastic framework. In the proposed anelastic LB model, mass and momentum conser...

A new compressible pressure-based Lattice Boltzmann Method is proposed to simulate humid air flows with phase change. The variable density and compressible effects are fully resolved, effectively lifting the Boussinesq approximation commonly used, e.g. for meteorological flows. Previous studies indicate that the Boussinesq assumption can lead to er...

A D2Q9 Hybrid Lattice Boltzmann Method (HLBM) is proposed for the simulation of both compressible subsonic and supersonic flows. This HLBM is an extension of the model of Feng et al. [1], which has been found, via different test cases, to be unstable for supersonic regimes. To circumvent this limitation, we propose:: (1) a new discretization of the...

Effect of density variations on mass conservation properties is widely recognized in the lattice Boltzmann method (LBM), thus non-conservative form of scalar transport equation was commonly adopted within the framework of hybrid LBM. Focusing on the compressible hybrid LBM, mass conservation and its effect on energy conservation equation are studie...

The effect of density variations on mass conservation properties is widely recognized in the lattice Boltzmann method (LBM), thus the non-conservative form of scalar transport equation was commonly adopted within the framework of hybrid LBM. Focusing on the compressible hybrid LBM, mass conservation and its effect on the energy conservation equatio...

A new explicit algebraic wall law for the Large Eddy Simulation of flows with adverse pressure gradient is proposed. This new wall law, referred as adverse pressure gradient power law (APGPL), is developed starting from the power-law of Werner and Wengle (Turbulent Shear Flows, vol 8, Springer, New York, pp 155–168, 1993) in order to mimic an impli...

This article presents a new numerical scheme designed to solve for any scalar equation coupled with a lattice Boltzmann solver (in so-called hybrid methods). Its most direct application is solving an energy equation, in parallel with a lattice Boltzmann solver, dealing with mass and momentum conservation. The numerical scheme is specifically design...

Based on recent work by [Guo et. al, JCP,109570(2020)], an improved thermal hybrid
recursive regularized lattice Boltzmann model (iHRR-ρ) on regular lattice is developed
for two and three-dimensional compressible laminar and turbulent flows. To enhance the
numerical stability in a broad range of Courant-Friedrichs-Lewy numbers and in under-resolved...

An improved coupling of immersed boundary method and turbulence wall models on Cartesian grids is proposed, for producing smooth wall surface pressure and skin friction at high Reynolds numbers. Spurious oscillations are frequently observed on these quantities with most immersed boundary wall modeling methods, especially for the skin friction which...

The von Neumann stability analysis along with a Chapman-Enskog analysis is proposed for a single-relaxation-time lattice Boltzmann Method (LBM) for wave propagation in isotropic linear elastic solids, using a regular D2Q9 lattice. Different boundary conditions are considered: periodic, free surface, rigid interface. An original absorbing layer mode...

Numerical investigation of skewed spatially evolving mixing layers - Volume 897 - M. Meldi, A. Mariotti, M. V. Salvetti, P. Sagaut

An original spectral study of the compressible hybrid lattice Boltzmann method (HLBM) on standard lattice is proposed. In this framework, the mass and momentum equations are addressed using the lattice Boltzmann method (LBM), while finite difference (FD) schemes solve an energy equation. Both systems are coupled with each other thanks to an ideal g...

The goal of this work is to determine classes of traveling solitary wave solutions for Lattice Boltzmann schemes by means of an hyperbolic ansatz. It is shown that spurious solitary waves can occur in finite-difference solutions of nonlinear wave equation. The occurence of such a spurious solitary wave, which exhibits a very long life time, results...

A new pressure-based Lattice-Boltzmann method (HRR-p) is proposed for the simulation of flows for Mach numbers ranging from 0 to 1.5. Compatible with nearest neighbor lattices (e.g. D3Q19), the model consists of a predictor step comparable to classical athermal Lattice-Boltzmann methods, appended with a fully local and explicit correction step for...

Grid refinement techniques are of paramount importance for Computational Fluid Dynamics approaches relying on the use of Cartesian grids. This is especially true of solvers dedicated to aerodynamics, in which the capture of thin shear layers require the use of small cells. In this paper, a three-dimensional grid refinement technique is developed wi...

The present study focuses on the unphysical effects induced by the use of non-uniform grids in the lattice Boltzmann method. In particular, the convection of vortical structures across a grid refinement interface is likely to generate spurious noise that may impact the whole computation domain. This issue becomes critical in the case of aeroacousti...

An efficient lattice Boltzmann (LB) model relying on a hybrid recursive regularization (HRR) collision operator on D3Q19 stencil is proposed for the simulation of three-dimensional high-speed compressible flows in both subsonic and supersonic regimes. An improved thermal equilibrium distribution function on D3Q19 lattice is derived to reduce the co...

The present study proposes a highly accurate lattice Boltzmann direct coupling cell-vertex algorithm, well suited for industrial purposes, making it highly valuable for aeroacoustic applications. It is indeed known that the convection of vortical structures across a grid refinement interface, where cell size is abruptly doubled, is likely to genera...

The present study focuses on the unphysical effects induced by the use of non-uniform grids in the lattice Boltzmann method. In particular, the convection of vortical structures across a grid refinement interface is likely to generate spurious noise that may impact the whole computation domain. This issue becomes critical in the case of aeroacousti...

A barotropic counterpart of the well-known convected vortex test case is rigorously derived from the Euler equations along with an athermal equation of state. Starting from a given velocity distribution corresponding to an intended flow recirculation, the athermal counterpart of the Euler equations are solved to obtain a consistent density field. T...

Data used to draw figures in article "ProLB: a Lattice-Boltzmann solver for large-eddy simulation of atmospheric boundary layer"

A D2Q9 Hybrid Lattice Boltzmann Method (HLBM) is proposed for the simulation of both compressible subsonic and supersonic flows. This HLBM is an extension of the model of Feng et al: [12], which has been found, via different test cases, to be unstable for supersonic regimes. The improvements consist of: (1) a new discretization of the lattice closu...

Complex geometries and open boundaries have been intensively studied in the nearly incompressible lattice Boltzmann method (LBM) framework. Therefore, only few boundary conditions for the high speed fully compressible LBM have been proposed. This paper deals with the definition of efficient boundary conditions for the compressible LBM methods, with...

Predicting and simulating aerodynamic fields for civil aircraft over wide flight envelopes represent a real challenge mainly due to significant numerical costs and complex flows. Surrogate models and reduced-order models help to estimate aerodynamic fields from a few well-selected simulations. However, their accuracy dramatically decreases when dif...

This article presents an original methodology for the prediction of steady turbulent aerodynamic fields. Due to the important computational cost of high-fidelity aerodynamic simulations, a surrogate model is employed to cope with the significant variations of several inflow conditions. Specifically, the Local Decomposition Method presented in this...

The numerical prediction of the vibroacoustic response of a submerged curved structure excited by a turbulent boundary layer remains a challenging scientific problem. One of the critical issue is the characterization of the turbulent loading. For instance the influence of the mean pressure gradient, induced by the curvature, on the fluctuating wall...

Gas-liquid flows are common in nuclear reactors under normal or accidental conditions. Several regimes may occur from dispersed regimes to stratified ones with some transitions between those regimes. 3D CFD codes are more and more used to investigate such complex flows. However, these codes are not yet mature especially for simulating regime transi...

An extended version of the hybrid recursive regularized lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regularized lattice Boltzmann approach well suited for high Reynolds numb...

Sound wave propagation in a shallow water environment is complex due to e.g. the uncertainties of sound speed profile being inhomogeneous and imprecisely measured, the bottom reflections, etc. The propagation and influence of several uncertainty parameters are quantified in this paper. A four-layer model, which can approximately represent a wide ra...

The canonical interaction between a two-dimensional weak Gaussian disturbance (en-tropy spot, density spot, weak vortex) with an exothermic/endothermic planar shock wave is studied via the Linear Interaction Approximation. To this end, a unified framework based on an extended Kovasznay decomposition that simultaneously accounts for non-acoustic den...

A thermal lattice Boltzmann model with a hybrid recursive regularization (HRR) collision operator is developed on standard lattices for simulation of subsonic and sonic compressible flows without shock. The approach is hybrid: mass and momentum conservation equations are solved using a lattice Boltzmann solver, while the energy conservation is solv...

The present work focuses on shape optimization using the lattice Boltzmann method applied to aerodynamic cases. The adjoint method is used to calculate the sensitivities of the drag force with respect to the shape of an object. The main advantage of the adjoint method is its cost, because it is independent from the number of optimization parameters...

An extension of the von Neumann linear analysis is proposed for the study of the discrete-velocity Boltzmann equati