Denis Ricot

• ProLB Technical Director & CAE Business development at CS GROUP

A novel quantum algorithm for solving the one-dimensional linear Navier-Stokes equations using the vorticity-stream function formulation and the lattice Boltzmann method as a numerical procedure is presented in this work. We start by presenting a state of the art of the current usage of quantum algorithms for solving ordinary and partial differenti...

Owing to its efficiency and aptitude for a massive parallelization, the lattice Boltzmann method generally outperforms conventional solvers in terms of execution time in weakly-compressible flows. However, the authorized time-step (being inversely proportional to the speed of sound) becomes prohibitively small in the incompressible limit, so that t...

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...

Purpose The Lattice Boltzmann (LB) method offers an alternative to conventional CFD methods. However, its practical use for complex turbulent flows of engineering interest is still at an early stage. In this paper, a lattice Boltzmann wall-modeled large-eddy simulation solver is outlined. Design/methodology/approach The solver is dedicated to co...

This study focuses on grid refinement techniques for the direct simulation of aeroacoustics, when using weakly compressible lattice Boltzmann models, such as the D3Q19 athermal velocity set. When it comes to direct noise computation, very small errors on the density or pressure field may have great negative consequences. Even strong acoustic densit...

This work aims to evaluate the base suction and drag modifications caused by a boundary layer manipulation due to large scale roughness prior its salient separation. A real car model, a Peugeot 208, and a squareback Ahmed body are both tested and compared in a scale 1 wind tunnel at 120 km/h with road effect and rotating wheels. The roughnesses are...

Both the unsteady aerodynamics force and base pressure distributions are investigated for four model cars in real flow conditions. The low pass cutoff frequency of the measurements is about 5 Hz which is sufficient to consider the global fluctuations of drag, lift and side forces. The drag fluctuations are very low, they never exceed 1% of the mean...

A cavity at the base of the squareback Ahmed model at Re 4 × 10 5 is able to reduce the base suction by 18% and the drag coefficient by 9%, while the geometry at the separation remains unaffected. Instantaneous pressure measurements at the body base, fluid force measurements and wake velocity measurements are investigated varying the cavity depth f...

Experiments are performed at industrial scales over the Ahmed geometry, i.e. at a Reynolds number of Re = 2.5 x 10(6) based on the height of the body. The shape of the squareback geometry is first optimized to make an initial substantial drag reduction. The separated flow at the trailing edge is orientated by introducing chamfers at the top and bot...

The Lattice Boltzmann method (LBM) is expected to provide a path to more and more realistic simulations of complex turbulent flows in engineering or environmental applications. However, to that end the LBM, which has originally been designed to simulate regular flows on sufficiently-fine uniform lattice, needs to be extended to handle turbulence mo...

A new three-dimensional CFD solver, LaBS, based on lattice Boltzmann algorithms has been developed in a framework of university and industry consortium. In this paper, this solver is used to simulate thermal flows, with a new thermal boundary condition for immersed solid boundary. The new proposed thermal boundary condition is based on the reconstr...

The flows past two different road vehicles with blunt after–bodies are studied at Reynolds numbers 10^7. The boundary layer thickness and the pressure distribution around the body are characterised. Then, the wake is investigated through static pressure and velocity measurements. Similar properties are obtained for both vehicles; in particular the...

The investigation of the wall pressure excitations over transportation vehicle panel is of great interest to improve the knowledge of vehicle interior noise transmission and also for future noise reduction strategies. A particularly useful task concerns the characterization and the separation of both acoustic and turbulent components of the wall pr...

In automotive industry, the acoustic comfort is become of primarily interest. Car window which is one of the relevant acoustic transmission paths, has to support two distinct pressure loadings: a Turbulent Boundary Layer excitation (turbulent component) and the acoustic component related to acoustic waves generated in the flow. In this study, Prope...

The vibroacoustic behavior of simply supported plate excited by aeroacoustic pressure field is investigated. Based on analytical expressions of the Cross Power Spectral Density (CPSD) of an acoustic diffuse field and of a turbulent flow (Corcos's model), a new method is implemented to perform a numerical synthesis of aeroacoustic wall-pressure fiel...

In order to properly address the simulation of complex (weakly compressible) turbulent flows, the lattice Boltzmann method, originally designed for uniform structured grids, needs to be extended to composite multi-domain grids displaying various levels of spatial resolution. Therefore, physical conditions must be specified to determine the mapping...

Due to acoustic comfort has become one of the principal concerns for car manufacturers, it is important to improve i) the knowledge of the car panel vibrations which are due to two different components: acoustic excitation and turbulent wall pressure one, and ii) the associated radiation in the car interior. In this paper, first, we propose to synt...

In most fluid mechanic applications, the dominant high energy content POD modes are generally well converged justifying the great use of POD to extract the associated large scale flow structures of a turbulent flow. However for particular studies related to the characterization of smaller flow structures, it is necessary to take into account high o...

Direct measurements of the wavenumber-frequency spectrum of wall pressure fluctuations beneath a turbulent plane channel flow have been performed in an anechoic wind tunnel. A rotative array has been designed that allows the measurement of a complete map, 63×63 measuring points, of cross-power spectral densities over a large area. An original post-...

The vibroacoustic behavior of simply supported plate excited by aeroacoustic pressure field is studied. The excitation pressure field is generated by a Cholesky decomposition of the analytical expression of the Power Cross-Spectral Density matrices. A set of random phases are used in order to generate different pressure field realizations. Corcos a...

Based on a 3D simulation of the air flow around a vehicle, the Extended Proper Orthogonal Decomposition (EPOD) is employed in order to identify the existing relation between aerodynamic events around the door mirror (Ω domain) and the near acoustic pressure field (S domain). The aerodynamic pressure field on a 2D plan of Ω is decomposed using a cla...

For high-Reynolds number flows, the lattice Boltzmann method suffers from numerical instabilities that can induce local blowup of the computation. The von Neumann stability analysis applied to the LBE-BGK and LBE-MRT models shows that numerical instabilities occur in the high wavenumber range and are due to the interplay between acoustic modes and...

Extended Proper Orthogonal Decomposition based on snapshot POD is used to investigate the correlation between the aerodynamic quantities of interest in an automotive ventilation outlet and the associated sound pressure field. A 3D simulation of the flow and the associated sound field of a real engineering application is obtained thanks to a Direct...

Computational aeroacoustic (CAA) simulation requires accurate schemes to capture the dynamics of acoustic fluctuations, which are weak compared with aerodynamic ones. In this paper, two kinds of schemes are studied and compared: the classical approach based on high order schemes for Navier–Stokes-like equations and the lattice Boltzmann method. The...

In this work we have numerically studied aeroacoustics of automotive ventilation outlets. Simulations are performed with the CFD software PowerFLOW based on Lattice Boltzmann method (LBM). Low dissipative LBM scheme enables to compute aeroacoustic sources generated by turbulence fluctuations and to propagate them in the same simulation. In a first...

The prediction of the vibratory response of structures excited by turbulent flows im-plies a good knowledge of both aerodynamic and acoustic components of the wall pressure fluctuations. In the present work, experiments were aimed at measuring wall pressure fluctuations under turbulent flows, in order to separate the two exciting loadings. The ex-p...

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in t...

A lattice Bolzmann code based on the two-dimensional nine-velocity model has been developed for computational aeroacoustic studies. The connection between the continuous and lattice Boltzmann equations is completely described for this model. A discrete-velocity Boltzmann equation is first derived and is integrated along a characteristic. The fully...

Coupling between vortex shedding over automotive sunroof and acoustic resonance of the passenger compartment can induce strong self-sustained oscillations of the flow. The maximum amplitude oscillation occurs when the frequency of an aerodynamic instability matches the resonance frequency of the vehicle. A detailed study of the phenomenon shows tha...

cote interne IRCAM: Misdariis00a

The accordion is a free‐reed instrument. The two identical reeds associated with one note are driven separately by the airflow created by the inward and outward movements of the bellows. In this present study, attention is focused on understanding the aerodynamic phenomena involved in reed vibration. The acoustical model is deduced from the variati...

Etude expérimentale et théorique du mécanisme d'excitation aéroacoustique des césures automobiles. Un travail expérimental et théorique sur les césures, petites cavités de faible longueur suivant l'axe de l'écoulement et situées au niveau de l'interstice entre deux portes ou entre une porte et la caisse du véhicule, est présenté ici. Bien que peu...

En aéroacoustique automobile, une partie du bruit intérieur généré par l’écoulement autour d’un véhicule provient de l’excitation des vitrages. Même si la modélisation physique de ce phénomène est classique, son application sur un cas industriel reste délicate en raison de la difficulté à séparer les composantes acoustiques et turbulentes de l’exci...