Scholars@Duke
Massimo Germano

Massimo Germano

Adjunct Professor in the Department of Civil and Environmental Engineering
Civil and Environmental Engineering
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Selected Publications

Mixed Averaging Procedures

Journal Article Flow, Turbulence and Combustion · April 1, 2024 The statistical operators typically applied in postprocessing numerical databases for statistically steady turbulence are a mixture of physical averages in homogeneous spatial directions and in time. Alternative averaging operators may involve phase or ens ... Full text Cite

Effect of Variable Density on Subgrid Scales

Chapter · January 1, 2024 Variable density flows are very common in nature, in technology and in industry. The numerical simulation of complex flows of applicative interest and with relevant variable density flows requires the truncation of turbulent scales of the resolved velocity ... Full text Cite

Turbulence Without Fluctuations

Chapter · April 29, 2023 Fluctuations are very important in statistics, but their use in the study of turbulent flows,particularly in the formulation and the analysis of Large Eddy Simulations, is not so essential. In the paper some historical and personal recollections on that ar ... Cite

Dynamic tensorial eddy viscosity model: Effects of compressibility and of complex geometry

Journal Article Physics of Fluids · February 1, 2022 A previous paper by Cimarelli et al. ["General formalism for a reduced description and modelling of momentum and energy transfer in turbulence,"J. Fluid Mech. 866, 865-896 (2019)] has shown that every decomposition of turbulent stresses is naturally approx ... Full text Cite

Coarse grained simulations of shock-driven turbulent material mixing

Journal Article Physics of Fluids · March 1, 2021 We revisit coarse-grained simulation strategies for turbulent material mixing applications involving shock-driven turbulence in the context of the Radiation Adaptive Grid Eulerian (xRAGE) hydrodynamics and Besnard-Harlow-Rauenzahn (BHR) Reynolds-averaged N ... Full text Cite

Analysis and modelling of the commutation error

Journal Article Fluids · January 1, 2021 A multiscale dynamic analysis of the commutation error, based on the filtering approach is performed. The similarity multiscale hypothesis proposed by Bardina (1983) and extended by Geurts and Holm (2006) to the commutation error is examined in detail and ... Full text Cite

The Filtering Approach as a Tool for Modeling and Analyzing Turbulence

Conference Springer Proceedings in Physics · January 1, 2021 The Filtering Approach (FA) is a simple multiscale method of analysis, it extends the statistical formalism to a generic filtering operator and main ingredients are the Generalized Central Moments (GCM) homomorphic to the Statistical Central Moments (SCM). ... Full text Cite

A Numerical Study of the Spanwise Turbulence Past a Cylinder Flow

Conference Springer Proceedings in Physics · January 1, 2021 Many flows of industrial interest and many important benchmark turbulent flows are statistically stationary in time and are provided with a spanwise direction of homogeneity. The numerical simulation of such flows is conditioned by the discretization in sp ... Full text Cite

Dynamic Bridging for Coarse Grained Simulations of Turbulent Material Mixing

Conference Springer Proceedings in Physics · January 1, 2021 We revisit coarse-grained simulation strategies for turbulent material mixing applications involving shock-driven turbulence, based on bridging LANL’s Radiation Adaptive Grid Eulerian (xRAGE)—implicit large-eddy simulation (ILES), and Besnard-Harlow-Rauenz ... Full text Cite

Dynamic Tensorial Eddy Viscosity and Turbulent Stresses

Conference Springer Proceedings in Physics · January 1, 2021 In the theoretical framework provided by an alternative decomposition of the turbulent stresses, a new formalism for their approximation and understanding has been proposed in [1] that spontaneously directs to a tensorial turbulent eddy viscosity. Based on ... Full text Cite

A study on the statistical convergence of turbulence simulations around a cylinder

Conference AIP Conference Proceedings · November 24, 2020 The turbulent flow around a circular cylinder at a Reynolds number equal to 3900 is studied by an implicit Large Eddy Simulation performed by means of a discontinuous Galerkin finite element solver. The average velocity field in the wake is evaluated and c ... Full text Cite

Dynamic bridging modeling for coarse grained simulations of shock driven turbulent mixing

Journal Article Computers and Fluids · March 15, 2020 We focus on simulating the consequences of material interpenetration and mixing arising from perturbations at shocked material interfaces, as vorticity is introduced by the impulsive loading of shock waves, e.g., as in Inertial Confinement Fusion (ICF) cap ... Full text Cite

Decomposition of Turbulent Fluxes from Filtered Data and Application to Turbulent Premixed Combustion Modelling

Journal Article Flow, Turbulence and Combustion · August 1, 2019 The exact reconstruction of statistical quantities from filtered data is a fundamental question in turbulence research. Filtered data can be either data from a Large Eddy Simulation (LES) or it can be experimental data with insufficient resolution to captu ... Full text Cite

General formalism for a reduced description and modelling of momentum and energy transfer in turbulence

Journal Article Journal of Fluid Mechanics · May 10, 2019 Based on hierarchies of filter lengths, the large eddy decomposition and the related subgrid stresses are recognized to represent generalized central moments for the study and modelling of the different modes composing turbulence. In particular, the subgri ... Full text Cite

On the richardson extrapolation of the reynolds stress with the systematic grid and model variation method

Chapter · January 1, 2019 A new operational Richardson extrapolation has been proposed to reconstruct the Reynolds stresses in LES. The method is based on three LES simulations as suggested in the Systematic Grid and Model Variation approach, and two new terms appear in the formali ... Full text Cite

A RANS assisted LES approach

Chapter · January 1, 2019 In the particular approach herein proposed, RANS and LES are combined in order to achieve a detailed description of turbulent flows without incurring in infeasible computational effort. This model is based on the hybrid filter approach proposed by Germano ... Full text Cite

On the eddy viscosity associated with the subgrid stresses

Chapter · January 1, 2019 Thanks to its simplicity and robustness, the models based on the eddy viscosity concept represent the most common procedure to introduce the effect of the unresolved scales in the equations of motion for the Large Eddy Simulation (LES) approach. Indeed, th ... Full text Cite

Reduced description and modelling of small-scale turbulence by means of a tensorial turbulent viscosity

Conference Springer Proceedings in Physics · January 1, 2019 Starting from an alternative decomposition of the subfilter stresses, we present a tensorial turbulent viscosity for a reduced description of small-scale turbulence. The formalism is based on velocity increments and, through the analysis of Direct Numerica ... Full text Cite

Mixed Averaging Procedures

Journal Article Flow, Turbulence and Combustion · April 1, 2024 The statistical operators typically applied in postprocessing numerical databases for statistically steady turbulence are a mixture of physical averages in homogeneous spatial directions and in time. Alternative averaging operators may involve phase or ens ... Full text Cite

Effect of Variable Density on Subgrid Scales

Chapter · January 1, 2024 Variable density flows are very common in nature, in technology and in industry. The numerical simulation of complex flows of applicative interest and with relevant variable density flows requires the truncation of turbulent scales of the resolved velocity ... Full text Cite

Turbulence Without Fluctuations

Chapter · April 29, 2023 Fluctuations are very important in statistics, but their use in the study of turbulent flows,particularly in the formulation and the analysis of Large Eddy Simulations, is not so essential. In the paper some historical and personal recollections on that ar ... Cite

Dynamic tensorial eddy viscosity model: Effects of compressibility and of complex geometry

Journal Article Physics of Fluids · February 1, 2022 A previous paper by Cimarelli et al. ["General formalism for a reduced description and modelling of momentum and energy transfer in turbulence,"J. Fluid Mech. 866, 865-896 (2019)] has shown that every decomposition of turbulent stresses is naturally approx ... Full text Cite

Coarse grained simulations of shock-driven turbulent material mixing

Journal Article Physics of Fluids · March 1, 2021 We revisit coarse-grained simulation strategies for turbulent material mixing applications involving shock-driven turbulence in the context of the Radiation Adaptive Grid Eulerian (xRAGE) hydrodynamics and Besnard-Harlow-Rauenzahn (BHR) Reynolds-averaged N ... Full text Cite

Analysis and modelling of the commutation error

Journal Article Fluids · January 1, 2021 A multiscale dynamic analysis of the commutation error, based on the filtering approach is performed. The similarity multiscale hypothesis proposed by Bardina (1983) and extended by Geurts and Holm (2006) to the commutation error is examined in detail and ... Full text Cite

The Filtering Approach as a Tool for Modeling and Analyzing Turbulence

Conference Springer Proceedings in Physics · January 1, 2021 The Filtering Approach (FA) is a simple multiscale method of analysis, it extends the statistical formalism to a generic filtering operator and main ingredients are the Generalized Central Moments (GCM) homomorphic to the Statistical Central Moments (SCM). ... Full text Cite

A Numerical Study of the Spanwise Turbulence Past a Cylinder Flow

Conference Springer Proceedings in Physics · January 1, 2021 Many flows of industrial interest and many important benchmark turbulent flows are statistically stationary in time and are provided with a spanwise direction of homogeneity. The numerical simulation of such flows is conditioned by the discretization in sp ... Full text Cite

Dynamic Bridging for Coarse Grained Simulations of Turbulent Material Mixing

Conference Springer Proceedings in Physics · January 1, 2021 We revisit coarse-grained simulation strategies for turbulent material mixing applications involving shock-driven turbulence, based on bridging LANL’s Radiation Adaptive Grid Eulerian (xRAGE)—implicit large-eddy simulation (ILES), and Besnard-Harlow-Rauenz ... Full text Cite

Dynamic Tensorial Eddy Viscosity and Turbulent Stresses

Conference Springer Proceedings in Physics · January 1, 2021 In the theoretical framework provided by an alternative decomposition of the turbulent stresses, a new formalism for their approximation and understanding has been proposed in [1] that spontaneously directs to a tensorial turbulent eddy viscosity. Based on ... Full text Cite

A study on the statistical convergence of turbulence simulations around a cylinder

Conference AIP Conference Proceedings · November 24, 2020 The turbulent flow around a circular cylinder at a Reynolds number equal to 3900 is studied by an implicit Large Eddy Simulation performed by means of a discontinuous Galerkin finite element solver. The average velocity field in the wake is evaluated and c ... Full text Cite

Dynamic bridging modeling for coarse grained simulations of shock driven turbulent mixing

Journal Article Computers and Fluids · March 15, 2020 We focus on simulating the consequences of material interpenetration and mixing arising from perturbations at shocked material interfaces, as vorticity is introduced by the impulsive loading of shock waves, e.g., as in Inertial Confinement Fusion (ICF) cap ... Full text Cite

Decomposition of Turbulent Fluxes from Filtered Data and Application to Turbulent Premixed Combustion Modelling

Journal Article Flow, Turbulence and Combustion · August 1, 2019 The exact reconstruction of statistical quantities from filtered data is a fundamental question in turbulence research. Filtered data can be either data from a Large Eddy Simulation (LES) or it can be experimental data with insufficient resolution to captu ... Full text Cite

General formalism for a reduced description and modelling of momentum and energy transfer in turbulence

Journal Article Journal of Fluid Mechanics · May 10, 2019 Based on hierarchies of filter lengths, the large eddy decomposition and the related subgrid stresses are recognized to represent generalized central moments for the study and modelling of the different modes composing turbulence. In particular, the subgri ... Full text Cite

On the richardson extrapolation of the reynolds stress with the systematic grid and model variation method

Chapter · January 1, 2019 A new operational Richardson extrapolation has been proposed to reconstruct the Reynolds stresses in LES. The method is based on three LES simulations as suggested in the Systematic Grid and Model Variation approach, and two new terms appear in the formali ... Full text Cite

A RANS assisted LES approach

Chapter · January 1, 2019 In the particular approach herein proposed, RANS and LES are combined in order to achieve a detailed description of turbulent flows without incurring in infeasible computational effort. This model is based on the hybrid filter approach proposed by Germano ... Full text Cite

On the eddy viscosity associated with the subgrid stresses

Chapter · January 1, 2019 Thanks to its simplicity and robustness, the models based on the eddy viscosity concept represent the most common procedure to introduce the effect of the unresolved scales in the equations of motion for the Large Eddy Simulation (LES) approach. Indeed, th ... Full text Cite

Reduced description and modelling of small-scale turbulence by means of a tensorial turbulent viscosity

Conference Springer Proceedings in Physics · January 1, 2019 Starting from an alternative decomposition of the subfilter stresses, we present a tensorial turbulent viscosity for a reduced description of small-scale turbulence. The formalism is based on velocity increments and, through the analysis of Direct Numerica ... Full text Cite

Decomposition of the Reynolds stress from filtered data

Journal Article Physical Review Fluids · November 1, 2018 The reconstruction of the Reynolds stress from data provided by a large-eddy simulation (LES) is commonly based on the assumption that the statistical average of the filtered LES quantities is the same as that of the unfiltered ones. As such, the Reynolds ... Full text Cite

Blending and nudging in fluid dynamics: Some simple observations

Journal Article Fluid Dynamics Research · August 11, 2017 Blending and nudging methods have been recently applied in fluid dynamics, particularly regarding the assimilation of experimental data into the computations. In the paper we formally derive the differential equation associated to blending and compare it t ... Full text Cite

Generalized logarithmic scaling for high-order moments of the longitudinal velocity component explained by the random sweeping decorrelation hypothesis

Journal Article Physics of Fluids · September 1, 2016 Expressions for the logarithmic variations of the normalized turbulent longitudinal velocity (u2p)1/p with normalized distance z/δ from a boundary for high-order (p) moments in the intermediate region of wall bounded flows characterized by thickness d are ... Full text Cite

Analysis of a hybrid RANS/LES model using RANS reconstruction

Conference Springer Proceedings in Physics · January 1, 2016 The Hybrid RANS/LES method proposed is based on the hybrid filter approach introduced by Germano in 2004. In this work, instead of using two explicit models respectively for LES and RANS, we use only a model for LES and we reconstruct the RANS field exploi ... Full text Cite

The similarity subgrid stresses associated to the approximate Van Cittert deconvolutions

Journal Article Physics of Fluids · March 19, 2015 In the paper, we derive directly the expressions of the subgrid stresses associated to the approximate Van Cittert deconvolutions and we discuss their similarity structure and properties. ... Full text Cite

On the hybrid RANS-LES of compressible flows

Journal Article Notes on Numerical Fluid Mechanics and Multidisciplinary Design · January 1, 2015 The formulation of a RANS-LES method for compressible flows faces many fundamental problems. The usual adoption of mass weighted, Favre, averages in the RANS region, and filtered Favre averages in the LES region produces additional difficulties to the conn ... Full text Cite

On the extension of the eddy viscosity model to compressible flows

Journal Article Physics of Fluids · April 14, 2014 In the paper the authors examine the extension of the eddy viscosity modeling approach to compressible large eddy simulation. On the basis of formal algebraic relations among the generalized central moments and the filtered Favre terms, a new compressible ... Full text Cite

A mixed RANS/LES model applied to the channel flow

Conference Springer Proceedings in Physics · January 1, 2014 In the paper we present some preliminary results related to a new LES approach, the mixed RANS/LES modelling technique that should exploit both the experience accumulated in RANS modelling, particularly near the wall, and the LES capabilities. This new app ... Full text Cite

The simplest decomposition of a turbulent field

Journal Article Physica D: Nonlinear Phenomena · February 1, 2012 In this paper we will present some recent results concerning the simplest decomposition of a turbulent field. The large scale filtering operator is simply given by the two-point sum in space and the associated fluctuation is given by the two-point differen ... Full text Cite

A new deconvolution approach

Conference ERCOFTAC Series · January 1, 2011 A new deconvolution method recently proposed by author [1] is developed and applied to the differential filters [2, 3], in the context of the large eddy simulation of turbulent flows and the related subgrid scale modeling. ... Full text Cite

LES of the channel flow in a non aligned system of coordinates

Conference Journal of Physics: Conference Series · January 1, 2011 This work investigates the sensitivity of LES to a rotation of the usual stream-aligned system of coordinates in the case of channel flow at Re τ = 180. In the new reference system the principal axes are not necessarily aligned with the streamwise and the ... Full text Cite

The simplest LES

Conference ERCOFTAC Series · January 1, 2010 The simplest large eddy simulation of a turbulent field is that produced by the two-point average, and it is intimately related to the two-point difference, basic ingredient of the small-scale turbulence theory, see Sreenivasan and Antonia for a recent rev ... Full text Cite

A new deconvolution method for large eddy simulation

Journal Article Physics of Fluids · January 1, 2009 In this paper we present and we briefly discuss a new way to derive approximate deconvolution subgrid models for the large eddy simulation of turbulent flows. © 2009 American Institute of Physics. ... Full text Cite

The filtering formulation of the mixed subgrid model

Journal Article Physics of Fluids · January 1, 2008 In this paper a new mixed model consistent with the filtering formulation has been derived as the subgrid model associated with the product GF of a similarity filter G with a functional filter F. The case where F is the Smagorinsky eddy viscosity filter is ... Full text Cite

The elementary energy transfer between the two-point velocity mean and difference

Journal Article Physics of Fluids · January 1, 2007 In this paper, the elementary energy transfer between the two-point average of a velocity field and the two-point difference has been examined. The equations related to the two-point quantities are derived from the Navier-Stokes equations applied to incomp ... Full text Cite

A direct relation between the filtered subgrid stress and the second order structure function

Journal Article Physics of Fluids · January 1, 2007 In this Brief Communication we rewrite the filtered subgrid stress in terms of velocity increments and we directly relate its mean value to the second order structure function. © 2007 American Institute of Physics. ... Full text Cite

On the filtering paradigm for LES of flows with discontinuities

Journal Article Journal of Turbulence · December 27, 2005 In this paper we have considered, from a theoretical point of view, the large eddy simulation (LES) of turbulent flows embedded with discontinuities like shocks flames, or interfaces. We have identified as main problems the occurence of parasitic contribut ... Full text Cite

Properties of the hybrid RANS/LES filter

Journal Article Theoretical and Computational Fluid Dynamics · August 1, 2004 One of the most important and challenging topics in the Large Eddy Simulation, of turbulent flows is the connection of the LES technique to the well known and largely used RANS approach where the Navier-Stokes equations are Reynolds averaged. The hybridati ... Full text Cite

On the physical effects of variable filtering lengths and times in LES

Journal Article Fluid Mechanics and its Applications · January 1, 2004 The Large Eddy Simulation of turbulent flows is based on the application of a filtering operator that separates the resolved eddies from the unresolved ones. If the flow is inhomogeneous this resolution is different from region to region, and different fil ... Full text Cite

On a possible direct effect of the eddy viscosity gradient in turbulence modeling

Journal Article Physics of Fluids · January 1, 2002 In this paper a possible direct effect of the eddy viscosity gradient in modeling the subgrid scale turbulent stress is argued on the grounds of simple heuristic arguments based on a multilevel decomposition of the turbulent field and on the gradient appro ... Full text Cite

Dynamic inverse modeling and its testing in large-eddy simulations of the mixing layer

Journal Article Physics of Fluids · January 1, 1999 We propose new identities for dynamic subgrid modeling in large-eddy simulation involving an explicit filter and its inverse. Exact defiltering of a class of numerical realizations of the top-hat filter is developed. The approach is applied to large-eddy s ... Full text Cite

A statistical formulation of the dynamic model

Journal Article Physics of Fluids · January 1, 1996 Two different large eddy simulations are statistically equivalent if they produce the same statistical representation. In this paper this basic definition is discussed in detail and a new formulation of the subgrid scale dynamic model that should force the ... Full text Cite

Turbulence the filtering approach

Journal Article Journal of Fluid Mechanics · January 1, 1992 EXplicit or implicit filtered representations of chaotic fields like spectral cut-offs or numerical discretizations are commonly used in the study of turbulence and particularly in the so-called large-eddy simulations. Peculiar to these representations is ... Full text Cite

A dynamic subgrid-scale eddy viscosity model

Journal Article Physics of Fluids A · January 1, 1991 One major drawback of the eddy viscosity subgrid-scale stress models used in large-eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in ... Full text Cite

The Dean equations extended to a helical pipe flow

Journal Article Journal of Fluid Mechanics · January 1, 1989 In this paper the Dean (1928) equations are extended to the case of a helical pipe flow, and it is shown that they depend not only on the Dean number K but also on a new parameter λ/ where λ is the ratio of the torsion τ to the curvature κ of the pipe axis ... Full text Cite

Potential flow in helical pipes

Journal Article Meccanica · March 1, 1987 In this paper we studied the potential flow in a helical pipe using an orthogonal system of coordinates fixed to the helical axis. The analysis was conducted both analitically by applying perturbative methods and numerically. Results show that the torsion ... Full text Cite

A proposal for a redefinition of the turbulent stresses in the filtered Navier–Stokes equations

Journal Article The Physics of Fluids · July 1, 1986 A redefinition of the Leonard term, the subgrid scale cross term, and the subgrid scale Reynolds stress is proposed, consistent with a general statement concerning turbulent stresses. The main advantage of the new redefined stresses consists of the ... Full text Cite

Differential filters of elliptic type

Journal Article The Physics of Fluids · June 1, 1986 Linear differential filters, i.e., filters in which the filtered function f̄ and the original function f are connected by a linear differential equation, are studied on a general basis concerning the elliptic operators of second order. In addition, ... Full text Cite

Differential filters for the large eddy numerical simulation of turbulent flows

Journal Article The Physics of Fluids · June 1, 1986 Differential filters for the large eddy numerical simulation of turbulent flows are defined and their properties are discussed. Their main advantages are that the correlations can be expressed exactly in the so-called resolvable scale and the atten ... Full text Cite

On the effect of torsion on a helical pipe flow

Journal Article Journal of Fluid Mechanics · January 1, 1982 An orthogonal coordinate system along a generic spatial curve has been introduced, and the Navier-Stokes equations for a steady incompressible viscous flow have been explicitly written in this frame of reference. As an application the flow in a helical pip ... Full text Cite

Radiant energy extraction from a gasdynamic laser. Static behavior

Journal Article Meccanica · June 1, 1975 The radiant energy extraction from a gasdynamic laser has been analyzed. The considered system of energy extraction is the MOPA one, in which the flowing gas medium is used as a Power Amplifier of a Master Oscillator, a primary laser beam introduced in the ... Full text Cite

EFFECT OF BREMSSTRAHLUNG RADIATION UPON BLAST WAVES.

Conference · January 1, 1975 The motion of a spherical blast wave in the range of very high Mach numbers is theoretically analyzed taking into account the loss of energy by free-free bremsstrahlung radiation. Numerical results are shown for different values of the characteristic param ... Cite

Line radiation in non local thermodynamic equilibrium

Journal Article Meccanica · September 1, 1970 This paper deals with the problem of line radiation in conditions of non thermodynamic equilibrium and applies the results obtained to the study of the imprisonment of resonance radiation. It was found that the excited level, and by consequence the resonan ... Full text Cite