Marcello Meldi

École nationale supérieure d'arts et métiers | ENSAM · Centre de Lille

An online Data Assimilation strategy based on the Ensemble Kalman Filter (EnKF) is used to study the features of parametric optimization and synchronization of the physical state when applied to scale-resolved numerical simulations. To this purpose, the method is combined with Large Eddy Simulation (LES) for the analysis of the turbulent flow in a...

The Benchmarck on the Aerodynamics of a Rectangular 5:1 Cylinder is studied using a data-driven technique which bridges numerical simulation and available experimental results. Because of intrinsic features of the tools used for investigation, in particular in terms of set-up and boundary conditions, significant discrepancies have been observed in...

The Benchmarck on the Aerodynamics of a Rectangular 5:1 Cylinder is studied using a data-driven technique which bridges numerical simulation and available experimental results. Because of intrinsic features of the tools used for investigation, in particular in terms of setup and boundary conditions, significant discrepancies have been observed in t...

An online Data Assimilation strategy based on the Ensemble Kalman Filter (EnKF) is used to improve the predictive capabilities of Large Eddy Simulation (LES) for the analysis of the turbulent flow in a plane channel, Re τ ≈ 550. The algorithm sequentially combines the LES prediction with high-fidelity, sparse instantaneous data obtained from a Dire...

A physics-infused strategy relying on the Ensemble Kalman Filter (EnKF) is here used to augment the accuracy of a continuous Immersed Boundary Method (IBM). The latter is a classical penalty method accounting for the presence of the immersed body via a volume source term which is included in the Navier-Stokes equations. The model coefficients of th...

A data-driven investigation of the flow around a high-rise building is performed combining heterogeneous experimental samples and RANS CFD. The coupling is performed using techniques based on the Ensemble Kalman Filter (EnKF), including advanced manipulations such as localization and inflation. The augmented state estimation obtained via EnKF has a...

In the present study, a discrete forcing Immersed Boundary Method (IBM) is proposed for the numerical simulation of high-speed flow problems including heat exchange. The flow field is governed by the compressible Navier-Stokes equations, which are resolved by using the open source library OpenFOAM. The numerical solver is modified to include source...

The potential for data-driven applications to scale-resolving simulations of turbulent flows is assessed herein. Multigrid sequential data assimilation algorithms have been used to calibrate solvers for Large Eddy Simulation for the analysis of the high-Reynolds-number flow around a rectangular cylinder of aspect ratio 5:1. This test case has been...

Essential features of the Multigrid Ensemble Kalman Filter (G. Moldovan, G. Lehnasch, L. Cordier, M. Meldi, A multigrid/ensemble Kalman filter strategy for assimilation of unsteady flows, Journal of Computational Physics 443-110481) recently proposed for Data Assimilation of fluid flows are investigated and assessed in this article. The analysis is...

Essential features of the Multigrid Ensemble Kalman Filter (G. Moldovan, G. Lehnasch, L. Cordier, M. Meldi, A multigrid/ensemble Kalman filter strategy for assimilation of unsteady flows, Journal of Computational Physics 443−110481) recently proposed for Data Assimilation of fluid flows are investigated and assessed in this article. The analysis is...

Highly resolved computations using Delayed Detached Eddy Simulations (DDES) of a canonical Windsor body are carried out. The flow around the car model, which is investigated imposing different yaw angles (up to 10°), is perturbed via a small square cylinder. This control element, whose length covers the whole height of the car model, is positioned...

In this paper we investigate whether the features of the nonequilibrium cascade, which have been identified in recent studies using high-fidelity tools, can be captured in the case of the classical dissipation scaling by turbulence closures based on the statistical description of freely decaying isotropic turbulence. Numerical results obtained usin...

A sequential estimator based on the Ensemble Kalman Filter for Data Assimilation of fluid flows is presented in this research work. The main feature of this estimator is that the Kalman filter update, which relies on the determination of the Kalman gain, is performed exploiting the algorithmic features of the numerical solver employed as a model. M...

Numerical calculations based on a recent version of the eddy-damped quasi-normal model (EDQNM-LMFA) are carried out for homogeneous isotropic turbulence (HIT) with the aim of investigating the dependency on the Reynolds number of second and third order velocity structure functions. The quantities investigated include the energy spectrum E, the non-...

In this paper we investigate whether the features of the non-equilibrium cascade, which have been identified in recent studies using high-fidelity tools, can be captured in the case of the classical dissipation scaling by turbulence closures based on the statistical description of freely decaying isotropic turbulence. Numerical results obtained usi...

A sequential estimator based on the Ensemble Kalman Filter for Data Assimilation of fluid flows is presented in this research work. The main feature of this estimator is that the Kalman filter update, which relies on the determination of the Kalman gain, is performed exploiting the algorithmic features of the numerical solver employed as a model. M...

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

An intrusive sequential estimator based on a Kalman filter approach for Data Assimilation of fluid flows is presented in this research work. The main feature of this estimator is that the Kalman filter update, which relies on the determination of the Kalman gain, is performed exploiting the algorithmic features of the numerical solver employed as a...

The accurate prediction of numerous bulk flow features of unstationary flows such as aerodynamic forces is driven by the precise representation of localized near-wall dynamics. Thus, the improvement in the prediction of near-wall flow features is a central target for the development of new investigative tools in Computational Fluid Dynamics (CFD).

Among the numerous research aspects in the analysis of complex flow configurations of industrial interest, the accurate prediction of turbulent flows is one of the ultimate open challenges. Investigation via classical tools, such as experiments and numerical simulation, is difficult because of fundamental drawbacks which can not be completely exclu...

The three-dimensional flow around a sphere is one of the most classical subjects of investigation for fundamental analysis of external aerodynamics. In fact this flow configuration, which is described by a very simple geometrical shape, exhibits the potential for complex multi-physics analysis. Some aspects that can be investigated include turbulen...

This paper investigates the effect of a finite Reynolds number (FRN) on the flatness factor ( $F$ ) of the velocity derivative in decaying homogeneous isotropic turbulence by applying the eddy damped quasi-normal Markovian (EDQNM) method to calculate all terms in an analytic expression for $F$ (Djenidi et al. , Phys. Fluids , vol. 29 (5), 2017 b ,...

The development of an improved IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows, and it is expanded for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically der...

A sensitivity analysis of new methodological approaches for state estimation (Meldi and Poux J. Comput. Phys. 347, 207–234, 2017) is proposed in this manuscript. The performance of the estimator is tested via the analysis of a number of aspects that play a major role in the augmented prediction process, such as the density in time sampling of avail...

The emergence of anomalous fast decay regimes in homogeneous isotropic turbulence (HIT) decay is investigated via both theoretical analysis and eddy-damped quasi-normal Markovian simulations. The work provides new insight about a fundamental issue playing a role in HIT decay, namely the influence of non-standard shapes of the energy spectrum, in pa...

This study assesses the ability of a sensitivity-based, span-wise homogeneous control velocity distributed at the surface of a circular cylinder to cut down the cost of reducing drag by more classical techniques, e.g., base bleed and lateral suction. At Reynolds number Re=100, achieving the linear optimal reduction requires a time-dependent control...

The development of an improved IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows and it is extended for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically deri...

Nowadays, large-eddy simulation (LES) is increasingly applied to complex flow configurations of interest in technological or environmental applications.

A Kalman filter based sequential estimator is presented in this work. The estimator is integrated in the structure of segregated solvers for the analysis of incompressible flows. This technique provides an augmented flow state integrating available observation in the CFD model, naturally preserving a zero-divergence condition for the velocity field...

The present work proposes a modified Pressure-Implicit Split-Operator (PISO) solver integrating the recent Immersed Boundary Method (IBM) proposed by [1] in order to perform reliable simulations of incompressible flows around bluff bodies using the open source toolbox OpenFOAM version 2.2 ([2]). The (IBM) allows for a precise representation of fixe...

The effects of the finiteness of the physical domain over the free decay of homogeneous isotropic turbulence are explored in the present article. Saturation at the large scales is investigated by the use of theoretical analysis and eddy-damped quasi-normal Markovian calculations. Both analyses indicate a strong sensitivity of the large-scale featur...

A Kalman filter based sequential estimator is presented in the present work. The estimator is integrated in the structure of segregated solvers for the analysis of incompressible flows. This technique provides an augmented flow state integrating available observation in the CFD model, naturally preserving a zero-divergence condition for the velocit...

The effects of time-lasting initial production mechanisms in homogeneous isotropic turbulence (HIT) decay are here investigated by the use of an eddy-damped quasi-normal Markovian (EDQNM) model. The statistical properties of these effects are included in the EDQNM model by the use of an ad-hoc term which mimics the turbulent energy production in gr...

In this paper, the Immersed Boundary Method (IBM) proposed by Pinelli is implemented for finite volume approximations of incompressible Navier-Stokes equations solutions in the open source toolbox OpenFOAM version 2.2. Solid obstacles are described using a discrete forcing approach for boundary conditions. Unlike traditional approaches encompassing...

In the present work the quantification of the time-lasting effects of production mechanisms in homogeneous isotropic turbulence decay is addressed. The analysis is developed through the use of theoretical tools as well as numerical calculations based on the eddy damped quasinormal Markovian (EDQNM) model. In both cases a modified Lin equation is us...

The present paper addresses the issue of finding key parameters that may lead to the occurrence of non-classical decay regimes for fractal/multiscale generated grid turbulence. To this aim, a database of numerical simulations has been generated by the use of the eddy-damped quasi-normal Markovian (EDQNM) model. The turbulence production in the wake...

The epistemic uncertainty in the free coefficients of two popular Reynolds-averaged Navier-Stokes (RANS) eddy-viscosity turbulence models is quantified. In particular, the Launder-Sharma low-Reynolds K − ε and the Menter K − ω SST models are considered. The free coefficients present in turbulence models are retrieved from some properties of benchma...

A new numerical formulation for the Eddy-Damped Quasi-Normal Markovian (EDQNM) model is proposed in the present paper. This formulation is based on an adaptive procedure that progressively modifies the spectral mesh at the large scales, forcing a resolution requirement set by the user. The resulting adaptive numerical method for the EDQNM model has...

The return to isotropy of freely decaying homogeneous axisymmetric turbulence is numerically studied using the Eddy-Damped Quasi-Normal Markovian closure. The model, whose classical formulation has been extended to moderately anisotropic flows by Cambon, Jeandel, and Mathieu [“Spectral modelling of homogeneous non-isotropic turbulence,” J. Fluid Me...

An investigation of some open issues in homogeneous isotropic turbulence (HIT) decay is proposed in the present paper. More specifically, several apparent paradoxical or controversial issues, among which the existence of solutions satisfying complete self-similarity and complete self-preservation, are investigated via theoretical analysis and numer...

The time evolution of initially non-self-similar regimes in isotropic turbulence decay is investigated by both theoretical analysis and EDQNM simulations. The breakdown of self-similarity is recovered by the analysis of a three-range energy spectrum, with two different slopes at scales larger than the integral length scale. The results of the analy...

The time evolution of the pressure spectrum E_p in freely decaying homogeneous isotropic turbulence (HIT) is investigated via Eddy-Damped Quasi-Normal Markovian(EDQNM) computations. It is well known that physical quantities associated to the energy spectrum evolve through power laws in HIT decay. For both low and high values of Reλ , the associated...

This paper presents an extension of existing works dealing with the dynamics of a passive scalar in freely decaying isotropic turbulence, by accounting for a production mechanism of the passive scalar itself. The physically relevant case of the temperature dynamics in the presence of Joule heating via the dissipation of the turbulent kinetic energy...

The flow-structure interactions streaming from the motion of an immersed solid body are investigated through an Arbitrary Lagrangian-Eulerian (ALE) approach applied to the Lattice Boltzmann method (LBM). The method is based on the use of a moving grid to describe the flow around the solid body, while the physical domain is resolved by the use of an...

The time evolution of pressure statistics in freely decaying homogeneous isotropic turbulence (HIT) is investigated via eddy-damped quasi-normal Markovian (EDQNM) computations. The present results show that the time decay rate of pressure-based statistical quantities, such as pressure variance and pressure gradient variance, are sensitive to the br...

Both theoretical analysis and eddy-damped quasi-normal Markovian (EDQNM) simulations are carried out to investigate the different decay regimes of an initially non-self-similar isotropic turbulence. Breakdown of self-similarity is due to the consideration of a composite three-range energy spectrum, with two different slopes at scales larger than th...

A stochastic approach based on generalized polynomial chaos (gPC) is used to quantify the error in large-eddy simulation (LES) of a spatially evolving mixing layer flow and its sensitivity to different simulation parameters, viz., the grid stretching in the streamwise and lateral directions and the subgrid-scale (SGS) Smagorinsky model constant (CS...

Statistical methodologies based on surrogate-models have proved to be an efficient approach to quantify the physical properties of turbulent flows. The underlying idea is to parametrize the space of possible solutions via a computationally inexpensive approximation model, which is then used to generate samples for the statistical tool at hand. In t...

We investigate the influence of uncertainties in the shape of the energy spectrum over the Smagorinsky ["General circulation experiments with the primitive equations. I: The basic experiment," Mon. Weather Rev. 91(3), 99 (1963)] subgrid scale model constant C(S): the analysis is carried out by a stochastic approach based on generalized polynomial c...

The development of methodologies aimed at obtaining new insights in the behavior of the error in Large-Eddy Simulation (LES) has recently gained considerable attention. A possible approach to estimate the error at moderate computational cost is to combine the response surface methodology with the generalized Polynomial Chaos (gPC) theory, in which...

A response surface based methodology is used to quantify the error in Large-Eddy Simulation (LES) of a spatially-evolving mixing layer flow and its sensitivity to different simulation parameters, viz. the grid stretching and the subgrid scale model constant. An algebraic error Cost Function (eCF) is evaluated with respect to the results of a highly...

A stochastic eddy-damped quasi-normal Markovian (EDQNM) approach is used to investigate self-similar decaying isotropic turbulence at a high Reynolds number (400 ≤ Reλ ≤ 104). The realistic energy spectrum functional form recently proposed by Meyers & Menevau (Phys. Fluids, vol. 20, 2008, p. 065109) is generalized by considering some of the model c...

The work addresses to a better comprehension of the error assessment in LES due to the coupling between the model and the numerical discretisation. The possibility to reduce the interactions between the error sources is investigated through the use of an algebraic function correlating the characteristics length of the subgrid model Delta(e) to the...