Marro Massimo

École Centrale de Lyon | ECL · Département Mécanique des Fluides - Acoustique - Energétique - MF.A.E.

We investigate the concentration fluctuations of passive scalar plumes emitted from small, localised (point-like) steady sources in a neutrally stratified turbulent boundary layer over a rough wall. The study utilises high-resolution large-eddy simulations for sources of varying sizes and heights. The numerical results, which show good agreement wi...

This study investigates the turbulent dispersion of pollutants in the wake of a two-dimensional square obstacle, focusing on assessing the reliability of turbulence closure models used in atmospheric pollutant dispersion. Utilizing Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV), we characterized the flow dynamics, identifying a...

We present an experimental investigation of the turbulent entrainment in non-Boussinesq steady plumes, focusing on three helium releases issued from an axisymmetric source, and with increasing Reynolds number. Two-dimensional instantaneous velocity fields, measured using particle image velocimetry (PIV), are exploited to compute first- and second-o...

The presence of vegetation within urban canyons leads to non-trivial patterns of the concentration of airborne pollutants, as a result of the complex structure of the velocity field. To investigate the relationship between concentration, velocity fields and vegetation density, we have performed wind-tunnel experiments in a reduced-scale street cany...

Drafting is a strategy in marathon running races that reduces the drag force acting on a designated runner. Drafting involves a formation of athletes, called pacers, running in front of (and sometimes behind) the designated runner. The present experiments evaluated complex formations involving up to seven pacers with the aim of enhancing the perfor...

We investigate the ventilation conditions required to control the propagation of smoke, produced by a tunnel fire, in the presence of two inertial forcings: a transverse extraction system and a longitudinal flow. For that purpose, we performed a series of experiments in a reduced-scale tunnel, using a mixture of air and helium to simulate the relea...

Greening cities is a key solution to improve the urban microclimate and mitigate the impact of climate change. However, the effect of tree planting on pollutant dispersion in streets is still a debated topic. To shed light on this issue, we present a wind-tunnel experiment aimed at investigating the effect of trees on street canyon ventilation. An...

Greening cities is a key solution to improve the urban microclimate and mitigate the impact of climate change. However, the effect of tree planting on pollutant dispersion in streets is still a debated topic. To shed light on this issue, we present a wind-tunnel experiment aimed at investigating the effect of trees on street canyon ventilation. An...

A reduced-scale experimental protocol, using an air-helium jet as the source, was designed to study the performance of a transverse smoke extraction system using two dampers. The type of system under investigation aims at preserving smoke stratification and confining the smoke within a limited zone. This strategy is appropriate for bidirectional or...

The urban environment represents an area with particular microclimatic characteristics, due to human activities and to the geometry of the buildings. Urbanization processes can alter the processes of heat, mass and exchange momentum between the ground and the atmosphere. The most important phenomenon is the formation of the so-called heat island (C...

Ventilation systems are fundamental in preventing disastrous consequences after road tunnel accidents. To improve our understanding, we have experimentally studied the ventilation conditions required to control the propagation of smoke produced by a tunnel fire in presence of a transversal extraction system and a longitudinal flow. Within a reduced...

The exacerbation of the urban heat island due to global warming poses a serious risk to the health of citizens. Furthermore, the alteration of the urban microclimate affects air quality with an expected increase in the concentrations of harmful pollutants. Greening cities is an effective tool to mitigate these effects. However, the effect of tree p...

Non-Gaussian statistics of large-scale fields are routinely observed in data from atmospheric and oceanic campaigns and global models. Recent direct numerical simulations (DNSs) showed that large-scale intermittency in stably stratified flows is due to the emergence of sporadic, extreme events in the form of bursts in the vertical velocity and the...

We propose a new experimental protocol to investigate the atmospheric dispersion of a dense gas in wind-tunnel experiments. Simultaneous measurements of concentration and velocity are performed by coupling a flame ionization detector (FID) and a hot-wire anemometer (HWA), whose probes are located sufficiently close to each other so that the respect...

Non-Gaussian statistics of large-scale fields are routinely observed in data from atmospheric and oceanic campaigns and global models. Recent direct numerical simulations (DNSs) showed that large-scale intermittency in stably stratified flows is due to the emergence of sporadic, extreme events in the form of bursts in the vertical velocity and the...

The understanding of the mechanics of turbulent dispersion is of primary importance in estimating the effects of mixing processes involved in a variety of events playing a significant role in our daily life. This motivates research on the characterization of statistics and the complex temporal evolution of passive scalars in turbulent flows. A key...

- top left panel: output visualization; - top right panel: passive scalar concentration PDFs, comparison between DNS results and gamma model; - bottom left panel: evolution of the concentration fluctuation intensity with the different mixing phases highlighted; - bottom right panel: mixing timescale.

An assessment of the impact of cruise ship emissions while hotelling in the port of Naples has been studied by means of wind tunnel and computational fluid dynamics (CFD) models. An area of about 1.2 km² was reproduced at a scale of 1:500 for the wind tunnel experiments. The worst but most emission scenario with three cruise ships emitting at the s...

Under crosswind conditions, road cyclists experience an extra drag force and a destabilising lateral force. In these conditions a group of cyclists manages to reorganise its spatial formation to minimise these forces forming an echelon, i.e a diagonal single pace line of riders staggered across the road, a configuration which is markedly different...

We review the efforts made by the scientific community in more than seventy years to elucidate the behaviour of concentration fluctuations arising from localized atmospheric releases of dynamically passive and non-reactive scalars. Concentration fluctuations are relevant in many fields including the evaluation of toxicity, flammability, and odour n...

We analyse the metrological aspect related to systems devoted to the simultaneous measurements of (one point) velocity and scalar concentration statistics. We consider systems based on the coupling of an anemometer (laser Doppler or hot wire) with a flame ionization detector. In particular, we focus on the estimate of the cross-correlation velocity...

In this paper the application of numerical and physical models for the simulation of airborne pollutants in urban areas are presented. The assessment of the impact of cruise ships during the hoteling phase in the port of Naples is considered as case study. A physical model of the urban area of Naples has been realized (scale 1:500) and tested in th...

The concentration of a passive scalar dispersed in a turbulent flow exhibits a complex stochastic dynamics. In this paper, we present a minimalist stochastic model that resembles the concentration statistics of a passive scalar emitted from a localized source in a neutral boundary layer. The model provides closed forms for the crossing rates and ti...

We derive a system of equations for the statistical moments of a passive scalar dispersed in a turbulent flow from the transport equation of the probability density function. We solve the system through a Green's function and we obtain a formally exact solution for the statistical moments of the passive scalar concentration. We use this solution to...

The dynamics of a passive scalar plume in a turbulent boundary layer is experimentally investigated via vertical turbulent transport time series. Experimental data are acquired in a rough-wall turbulent boundary layer that develops in a recirculating wind tunnel setup. Two source sizes in an elevated position are considered in order to investigate...

The dynamics of a passive scalar plume in a turbulent boundary layer is experimentally investigated via vertical turbulent transport time-series. Data are acquired in a rough-wall turbulent boundary layer that develops in a recirculating wind tunnel set-up. Two source sizes in an elevated position are considered in order to investigate the influenc...

We carried out a series of experiments in a small-scale tunnel to study the confinement of smoke flow between two exhaust vents located on either side of a buoyant source placed at ground level within a ventilated tunnel. The objective of our study is to quantify the influence of the shape and the position (with respect to the tunnel axis) of the d...

In this work, experimental data of passive scalar plumes in a turbulent boundary layer are investigated. The experiments are performed in a wind tunnel where a passive scalar is injected through an L-shaped tube. Two source configurations are analysed for two different tube diameters. The passive scalar concentration is then measured at different d...

A series of experiments were conducted to investigate the effect of solid barriers, placed at the tunnel ceiling, on the behaviour of smoke in fire events within longitudinally ventilated tunnels, namely on the smoke back-layering lengths and on the critical velocity. For this purpose, we considered two types of barrier: "small barriers" designed t...

The characterization of pollutant transport is crucial for the analysis and modeling of the atmospheric boundary layer [1]. In this work, experimental data of passive scalar plumes in a turbulent boundary layer are investigated. The experiments are performed in a wind tunnel where the passive scalar is injected through an L-shaped tube located at z...

We analyze the reliability of the Lagrangian stochastic micromixing method in predicting higher-order statistics of the passive scalar concentration induced by an elevated source (of varying diameter) placed in a turbulent boundary layer. To that purpose we analyze two different modelling approaches by testing their results against the wind-tunnel...

The prediction of the probability density function of a pollutant concentration within atmospheric flows is of primary importance in estimating the hazard related to accidental releases of toxic or flammable substances and their effects on human health. This need motivates studies devoted to the characterization of concentration statistics of pollu...

We investigate the reliability of a meandering plume model in reproducing the passive scalar concentration statistics due to a continuous release in a turbulent boundary layer. More specifically, we aim to verify the physical consistency of the parametrizations adopted in the model through a systematic comparison with experimental data. In order to...

The prediction of the flow dynamics produced by the interaction between a sheared turbulent flow and a bluff body has important implications in the domain of the wind engineering and for what concerns the simulation of atmospheric dispersion of air-born pollutants. In this study we present the results of the experimental investigation on the wake o...

This study presents the performances of an inverse modelling approach aiming to identify position and emission rate of a localised pollutant source placed within a city district. To that purpose we combine wind tunnel experiments and an urban dispersion model. Experiments are performed in an idealised urban canopy, made up of regularly spaced block...

We use a Lagrangian stochastic micromixing model to predict the concentration fluctuations of a continuous release in a neutral boundary layer. We present the computational algorithm that implements the interaction by exchange with the conditional mean model and we compare the numerical solutions with the experimental values in order to evaluate th...

This study focuses on the influence of emission conditions—velocity and temperature—on the dynamics of a buoyant gas release in the atmosphere. The investigations are performed by means of wind tunnel experiments and numerical simulations. The aim is to evaluate the reliability of a Lagrangian code to simulate the dispersion of a plume produced by...

This study is devoted to the analysis of turbulent dispersion of light gases emitted from a punctual source in the atmospheric boundary layer and to their mathematical modelling. The investigations are performed by means of wind tunnel experiments and numerical simulations. The aim is to develop a Lagrangian code that simulates the dispersion of a...

This study presents the performances of an inverse modelling approach aiming in identifying position and emission rate of a localised pollutant source placed within a city district. To that purpose we combine wind tunnel experiments and an urban dispersion model. Experiments are performed in an idealised urban canopy, made up of regularly spaced bl...

The aim of the present paper is to investigate the viability of macroscopic traffic models for modeling and testing different traffic scenarios, in order to define the impact on air quality of different strategies for the reduction of traffic emissions. To this aim, we complement a well assessed traffic model on networks (Garavello and Piccoli (200...

The turbulent exchange of momentum between a two-dimensional cavity and the overlying boundary layer has been studied experimentally, using hot-wire anemometry and particle image velocimetry (PIV). Conditions within the boundary layer were varied by changing the width of the canyons upstream of the test canyon, whilst maintaining the square geometr...

The flow past rectangular cylinders has been investigated by two different numerical techniques, an adaptive finite-element (AFEM) and a finite-volume method (FVM). A square and a rectangular cylinder with width-to-height equal to 5 are taken into account. 2D computations have been performed for different Reynolds numbers in order to consider diffe...

In this paper we propose two error indicators aimed at estimating the space discretization error and the time discretization error for the unsteady Navier–Stokes equations. We define a space error indicator for evaluating the quality of the mesh and a time error indicator for evaluating the time discretization error. Moreover, we verify the reliabi...

Much of the existing European legislation on railway noise impact assessment refers to indicators based on long term weighted averages of acoustic intensities (L dn , L den , L eq). However, several studies have pointed out that noise event indicators are more appropriate in order to evaluate annoyance due to intermittent noise sources, such as tho...

In this paper we apply to the unsteady Navier–Stokes problems some results concerning a posteriori error estimates and adaptive algorithms known for steady Navier–Stokes, unsteady heat and reaction-convection-diffusion equations and unsteady Stokes problems. Our target is to investigate the real viability of a fully combined space and time adaptivi...

The flow past a rectangular cylinder with width-to-height equal to 5 has been investigated by two different numerical techniques, an adaptive finite-element (AFEM) and a finite-volume (FVM) method. 2D and 3D computations have been performed for different Reynolds numbers in order to analyze turbulent flow regimes and study the effect of the three-d...