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Marco CRIALESI ESPOSITO

Ricercatore t.d. art. 24 c. 3 lett. A
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2023 - Comparison of turbulent drop breakup in an emulsification device and homogeneous isotropic turbulence: Insights from numerical experiments [Articolo su rivista]
Olad, P; Innings, F; Crialesi-Esposito, M; Brandt, L; Hakansson, A
abstract

Turbulent emulsification is of considerable industrial interest. Nevertheless, numerical experiments (direct nu-merical simulations, DNS, with highly resolved interface tracking) have been mainly used to study drop breakup in idealized flows. This study, therefore, compares drop breakup in two different settings (homogenous and isotropic flow, and a simplified high-pressure homogenizer) with the intention of better understanding how insight gained from the idealized systems can be applied to industrially relevant devices. The flow differs be-tween the two cases, with highly anisotropic and inhomogeneous turbulence in the latter. Results show simi-larities between the two cases regarding morphology of breakup, suggesting that the underlying mechanism, as a function of Weber number, is similar. However, differences are also observed, e.g., in terms of breakup time and deformed morphology, which are associated with the locality of the turbulence in the homogenizer. Implications for an improved understanding of turbulent breakup in industrially relevant devices are discussed.

2023 - Droplet dynamics in homogeneous and isotropic turbulence [Relazione in Atti di Convegno]
Chibbaro, Sergio; CRIALESI ESPOSITO, Marco; Brandt, Luca
abstract

2023 - FluTAS: A GPU-accelerated finite difference code for multiphase flows [Articolo su rivista]
CRIALESI ESPOSITO, Marco; Nicolò, Scapin; Demou, Andreas D.; Marco Edoardo Rosti, ; Pedro, Costa; Filippo, Spiga; Luca, Brandt
abstract

2023 - Intermittency in turbulent emulsions [Articolo su rivista]
Crialesi-Esposito, M.; Boffetta, G.; Brandt, L.; Chibbaro, S.; Musacchio, S.
abstract

2023 - The interaction of droplet dynamics and turbulence cascade [Articolo su rivista]
CRIALESI ESPOSITO, Marco; Chibbaro, Sergio; Brandt, Luca
abstract

The dynamics of droplet fragmentation in turbulence is described by the Kolmogorov-Hinze framework. Yet, a quantitative theory is lacking at higher concentrations when strong interactions between the phases and coalescence become relevant, which is common in most flows. Here, we address this issue through a fully-coupled numerical study of the droplet dynamics in a turbulent flow at R-lambda & AP; 140, the highest attained up to now. By means of time-space spectral statistics, not currently accessible to experiments, we demonstrate that the characteristic scale of the process, the Hinze scale, can be precisely identified as the scale at which the net energy exchange due to capillarity is zero. Droplets larger than this scale preferentially break up absorbing energy from the flow; smaller droplets, instead, undergo rapid oscillations and tend to coalesce releasing energy to the flow. Further, we link the droplet-size distribution with the probability distribution of the turbulent dissipation. This shows that key in the fragmentation process is the local flux of energy which dominates the process at large scales, vindicating its locality.

2022 - A criterion for when an emulsion drop undergoing turbulent deformation has reached a critically deformed state [Articolo su rivista]
Hakansson, A; Crialesi-Esposito, M; Nilsson, L; Brandt, L
abstract

Turbulent breakup in emulsification devices is a dynamic process. Small viscous drops undergo a sequence of oscillations before entering the monotonic deformation phase leading to breakup. The turbulence-interface interactions prior to reaching critical deformation are therefore essential for understanding and modeling breakup. This contribution uses numerical experiments to characterize the critically deformed state (defined as a state from which breakup will follow deterministically, even if no further external stresses would act on the drop). Critical deformation does not coincide with a threshold maximum surface area, as previously suggested. A drop is critically deformed when a neck has formed locally with a curvature such that the Laplace pressure exceeds that of the smallest of the bulbs connected by the neck. This corresponds to a destabilizing internal flow, further thinning the neck. Assuming that the deformation leads to two spherical bulbs linked by a cylindrical neck, the critical deformation is achieved when the neck diameter becomes smaller than the radius of the smallest bulb. The role of emulsifiers is also discussed.

2022 - A Direct Numerical Simulation Investigation of the One-Phase Flow in a Simplified Emulsification Device [Articolo su rivista]
Olad, Peyman; CRIALESI ESPOSITO, Marco; Brandt, Luca; Innings, Fredrik; Hakansson, Andreas
abstract

More detailed investigation of the flow inside emulsification devices, e.g., High-pressure homogenizers (HPHs) helps the industry to broaden the fundamental understanding of the working principle of these machines which in turn will pave the road to increase the breakup efficiency of emulsification processes. Direct numerical simulation (DNS) is not deemed as a practical method in industry due to the high computational cost and time. This study is the first DNS carried out on a model of an emulsification device model. The goal of this study is to set a benchmark for future CFD investigations using industrially favorable tools (RANS, LES, etc.). A scale-up model HPH is designed and the results show a successful modeling of the flow field mimicking the flow behavior inside a typical HPH.

2022 - Effects of isotropic and anisotropic turbulent structures over spray atomization in the near field [Articolo su rivista]
CRIALESI ESPOSITO, Marco; Gonzalez-Montero, L. A.; Salvador, F. J.
abstract

Sprays and atomization processes are extremely diffused both in nature and in industrial applications. In this paper we analyze the influence of the nozzle turbulence on primary atomization, focusing on the resulting turbulent field and atomization patterns in the Near Field (NF). In order to do so, a Synthetic Boundary Condition (SBC) and a Mapped Boundary Condition (MBC), producing respectively isotropic and anisotropic turbulent fields, have been generated as inflow conditions for the spray Direct Numerical Simulations (DNS). We present a specific methodology to ensure consistency on turbulence intensity and integral lengthscale between the two inflows. The analysis performed on the turbulent field (using one-point statistics and spectrum analysis) reveals a significantly stronger turbulent field generated by the inflow boundary conditions with anisotropic structures. While the increased turbulence field generated in the MBC case results in a higher number of droplets generated, the probability functions of both cases are extremely similar, leading to the non-obvious conclusion that the atomization patterns are only slightly affected by the inflow condition. These considerations are supported by the analysis of droplet size distributions, radial distribution functions, axial and radial distributions, highlighting extremely similar behaviors between the MBC and the SBC cases. Finally, these analyses and their computations are presented in detail, underlining how this type of point-process characterization shows interesting potential in future studies on sprays.

2022 - Modulation of homogeneous and isotropic turbulence in emulsions [Articolo su rivista]
CRIALESI ESPOSITO, Marco; Edoardo Rosti, Marco; Chibbaro, Sergio; Brandt, Luca
abstract

We present a numerical study of emulsions in homogeneous and isotropic turbulence (HIT) at Re-lambda = 137. The problem is addressed via direct numerical simulations, where the volume of fluid is used to represent the complex features of the liquid-liquid interface. We consider a mixture of two iso-density fluids, where fluid properties are varied with the goal of understanding their role in turbulence modulation, in particular the volume fraction (0.03 < alpha < 0.5), viscosity ratio (0.01 < mu(d)/mu(c) < 100) and large-scale Weber number (10.6 < We(L) < 106.5). The analysis, performed by studying integral quantities and spectral scale-by-scale analysis, reveals that energy is transported consistently from large to small scales by the interface, and no inverse cascade is observed. Furthermore, the total surface is found to be directly proportional to the amount of energy transported, while viscosity and surface tension alter the dynamic that regulates energy transport. We also observe the -10/3 and -3/2 scaling on droplet size distributions, suggesting that the dimensional arguments that led to their derivation are verified in HIT conditions.

2022 - Towards best practice recommendations for turbulence modelling of high-pressure homogenizer outlet chambers - Numerical validation using DNS data [Articolo su rivista]
Olad, P; Esposito, Mc; Brandt, L; Innings, F; Hakansson, A
abstract

There is a large interest in predicting high-pressure homogenizer (HPH) valve hydrodynamics using CFD, in academic research and industrial R&D. Most of these studies still use two-equation RANS turbulence models, whereas only a few have used LES formulations. From a theoretical perspective, LES is known to be more accurate than RANS, especially in terms of estimating the dissipation rate of turbulent kinetic energy, which is the most important parameter needed for predicting efficiency using a population balance equation (PBE). However, LES also comes at a considerably higher computational cost. To choose the appropriate modelling approach, it is important to understand how much the accuracy and the computational cost increase between RANS and LES.This study provides the first validation of high-pressure homogenizer hydrodynamics, comparing RANS and a well-resolved LES to numerical experimental validation data of direct numerical simulation (DNS), on a model of the gap outlet jet. The LES does result in a higher accuracy throughout, but the differences are relatively small, when focusing on the flow inside the jet. When using the CFD results to predict maximum surviving drop diameter, the LES results in a relative error of 4.8% whereas the RANS leads to a relative error of 18%. Both errors are substantially smaller than those from a traditional scale-based equation instead of a CFD-PBE. When seen in the substantial reduction of computational time (a factor of 970), results illustrate how RANS could remain a viable supplementary technique for CFD modelling of HPHs, despite its many limitations. Best practice recommendations for obtaining this RANS performance is discussed.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

2021 - A mass-momentum consistent, Volume-of-Fluid method for incompressible flow on staggered grids [Articolo su rivista]
Arrufat, T.; Crialesi-Esposito, M.; Fuster, D.; Ling, Y.; Malan, L.; Pal, S.; Scardovelli, R.; Tryggvason, G.; Zaleski, S.
abstract

The computation of flows with large density contrasts is notoriously difficult. To alleviate the difficulty we consider a discretization of the Navier-Stokes equation that advects mass and momentum in a consistent manner. Incompressible flow with capillary forces is modeled and the discretization is performed on a staggered grid of Marker and Cell type. The Volume-of-Fluid method is used to track the interface and a Height-Function method is used to compute surface tension. The advection of the volume fraction is performed using either the Lagrangian-Explicit/CIAM (Calcul d'Interface Affine par Morceaux) method or the Weymouth and Yue (WY) Eulerian-Implicit method. The WY method conserves fluid mass to machine accuracy provided incompressibility is satisfied. To improve the stability of these methods momentum fluxes are advected in a manner "consistent" with the volume-fraction fluxes, that is a discontinuity of the momentum is advected at the same speed as a discontinuity of the density. To find the density on the staggered cells on which the velocity is centered, an auxiliary reconstruction of the density is performed. The method is tested for a droplet without surface tension in uniform flow, for a droplet suddenly accelerated in a carrying gas at rest at very large density ratio without viscosity or surface tension, for the Kelvin-Helmholtz instability, for a 3mm-diameter falling raindrop and for an atomizing flow in air-water conditions. (C) 2020 The Authors. Published by Elsevier Ltd.

2021 - PArallel, Robust, Interface Simulator (PARIS) [Articolo su rivista]
Aniszewski, W.; Arrufat, T.; Crialesi-Esposito, M.; Dabiri, S.; Fuster, D.; Ling, Y.; Lu, J.; Malan, L.; Pal, S.; Scardovelli, R.; Tryggvason, G.; Yecko, P.; Zaleski, S.
abstract

Paris (PArallel, Robust, Interface Simulator) is a finite volume code for simulations of immiscible multifluid or multiphase flows. It is based on the ?one-fluid?formulation of the Navier?Stokes equations where different fluids are treated as one material with variable properties, and surface tension is added as a singular interface force. The fluid equations are solved on a regular structured staggered grid using an explicit projection method with a first-order or second-order time integration scheme. The interface separating the different fluids is tracked by a Front-Tracking (FT) method, where the interface is represented by connected marker points, or by a Volume-of-Fluid (VOF) method, where the marker function is advected directly on the fixed grid. Paris is written in Fortran95/2002 and parallelized using MPI and domain decomposition. It is based on several earlier FT or VOF codes such as Ftc3D, Surfer or Gerris. These codes and similar ones, as well as Paris, have been used to simulate a wide range of multifluid and multiphase flows.Program summaryProgram Title: PArallel Robust Interface Simulator ? ParisCPC Library link to program files: https://doi.org/10.17632/5cb2yrfx7r.1Licensing provisions: GPLv3. Programming language: Fortran95/2002. Parallelized using MPI and domain decomposition. Nature of problem: Paris is a free code, or software, for computational fluid dynamics (CFD) of multiphase flows (or computational multiphase fluid dynamics (CMFD)), specialized in the numerical simulation of interfacial fluid flows, involving droplets, bubbles and waves, as described in the book by Tryggvason, Scardovelli and Zaleski [1]. It solves the Euler or Navier?Stokes equations in the one-fluid formulation of two-phase flow, including a surface tension force. It computes complex flows such as fast atomizing jets or droplets, expanding cavitation bubble clusters and multiphase flow through porous media.Solution method: The code mostly implements the methods described in the book by Tryggvason, Scardovelli and Zaleski [1]. Time stepping is performed using a first-order or a second-order in time predictor?corrector method with an explicit projection step for the pressure. Spatial discretization is by finite volumes on a regular cuboid grid. Interface tracking is performed with the Front-Tracking (FT) method or the Volume-of-Fluid (VOF) method. In the VOF version Paris uses either the LagrangianExplicit (LE) advection method or the exactly mass-conserving method of Weymouth and Yue [2]. The normal computation is performed using the Mixed-Youngs-Centered (MYC) scheme. A mass? momentum advection method has been also implemented that is consistent with the VOF advection [3]. Curvature is computed with the Height Function (HF) method. This is combined with the balanced Continuous Surface Force (CSF) method to compute surface tension forces.

2020 - Study of turbulence in atomizing liquid jets [Articolo su rivista]
Torregrosa, Antonio J.; Raúl, Payri; Javier Salvador, F.; CRIALESI ESPOSITO, Marco
abstract

Among the many unknowns in the study of atomizing sprays, defining an unambiguous way to analyze turbulence is, perhaps, one of the most limiting ones. The lack of proper tools for the analysis of the turbulence field (e.g. specific one/two-point statistics, spectrum, structure functions) limits the understanding of the overall phenomenon occurring, impeding the correct estimation of motion scales (from the Kolmogorov one to the integral one). The present work proposes a methodology to analyze the turbulence in atomizing jets using a pseudo-fluid method. The many challenges presented in these types of flows (such as temporal fluid properties uncertainties, strong anisotropy and lack of a priori chance of determining the motion scales) can be simplified by such a method, as it will be clearly shown by the smooth results obtained. Finally, the method is tested against the one-phase flows turbulent data available in the literature for the Kolmogorov scaling of the one-dimension energy spectra, showing how a pseudo-fluid method could provide a reliable tool to analyze multiphase turbulence, especially in spray's primary atomization. (C) 2020 Elsevier Ltd. All rights reserved.

2018 - Analysis on the effects of turbulent inflow conditions on spray primary atomization in the near-field by direct numerical simulation [Articolo su rivista]
Salvador, F. J.; Ruiz, S.; Crialesi-Esposito, M.; Blanquer, I.
abstract

It is widely acknowledged that the development of sprays in the near-field is of primary importance for the spray formation downstream, as it affects both the spray angle, as well as the intact core length. In this frame, the present work aims to study the effects of turbulence inlet boundary condition on the spray formation by means of Direct Numerical Simulations on a real condition at low Reynolds number. To this extent, the code Paris-Simulator has been used, while a digital filter-based algorithm was used in order to generate synthetic turbulence at the inlet boundary condition. The influence of turbulence intensity and lengthscale on the atomization process has been studied and analyzed through 3 simulation for which these parameters have been varied. The results clearly highlight how the atomization is heavily affected by the inlet turbulence configuration. An analysis of the different atomizing conditions has been conducted, aiming to understand how the variation introduced by the inlet boundary condition on the velocity field is affecting the local atomization dynamics. (C) 2018 Elsevier Ltd. All rights reserved.

2018 - Comparative study of the internal flow in diesel injection nozzles at cavitating conditions at different needle lifts with steady and transient simulations approaches [Articolo su rivista]
Salvador, Fj; De la Morena, J; Crialesi-Esposito, M; Martinez-Lopez, J
abstract

The motion of the needle during the injection process of a diesel injector has a marked influence on the internal flow, the fuel characteristics at the nozzle exit, the spray pattern and the fuel-air mixing process. The current paper is focused on the computational study of the internal flow and cavitation phenomena during the injection process, with inclusion of the opening where the needle is working at partial lifts. This study has been performed with a homogeneous equilibrium model (OpenFOAM) customized by the authors to simulate the real motion of the needle. The first part of the study covers the analysis of the whole injection process with a moving mesh using the boundary conditions provided by a one-dimensional (1D) model of the injector created in AMESim. This 1D model has offered the possibility of reproducing the movement of the needle with real lift law and real injection pressure evolution during the injection. Thus, it has been possible to compare the injection rate profiles provided by OpenFOAM against those obtained both in AMESim and experimentally. The second part compares the differences in mass flow, momentum flux, effective velocity and cavitation appearance between steady (fixed lifts) and transient (moving mesh) simulations. The aim of this comparison is to establish the differences between these two approaches. On the one hand is a more realistic approach in its use of transient simulations of the injection process and where the needle movement is taken into account. On the other hand, is the use of steady simulations at partial needle lifts. This analysis could be of interest to researchers devoted to the study of the diesel injection process since it could help to delimit the uncertainties involved in using the second approach which is more easily carried out, versus the first which is supposed to provide more realistic results.

2018 - Determination of critical operating and geometrical parameters in diesel injectors through one dimensional modelling, design of experiments and an analysis of variance [Articolo su rivista]
Salvador, Fj; Carreres, M; Crialesi-Esposito, M; Plazas, Ah
abstract

In this paper, a design of experiments and a statistical analysis of variance (ANOVA) are performed to determine the parameters that have more influence on the mass flow rate profile in diesel injectors. The study has been carried out using a one dimensional model previously implemented by the authors. The investigation is split into two different parts. First, the analysis is focused on functional parameters such as the injection and discharge pressures, the energizing time and the fuel temperature. In the second part, the influence of 37 geometrical parameters, such as the diameters of hydraulic lines, calibrated orifices and internal volumes, among others, are analysed. The objective of the study is to quantify the impact of small variations in the nominal value of these parameters on the injection rate profile for a given injector operating condition. In the case of the functional parameters, these small variations may be attributed to possible undesired fluctuations in the conditions that the injector is submitted to. As far as the geometrical and flow parameters are concerned, the small variations studied are representative of manufacturing tolerances that could influence the injected mass flow rate. As a result, it has been noticed that the configuration of the inlet and outlet orifices of the control volume, together with the discharge coefficient of the inlet orifice, among a few others, play a remarkable role in the injector performance. The reason resides in the fact that they are in charge of controlling the behaviour of the pressure in the control volume, which importantly influences injector dynamics and therefore the injection process. Variations of only 5% in the diameter of these orifices strongly modify the shape of the rate of injection curve, influencing both the injection delay and the duration of the injection process, consequently changing the total mass delivered.

2018 - Experimental investigation of the effect of orifices inclination angle in multihole diesel injector nozzles. Part 1-Hydraulic performance [Articolo su rivista]
Salvador, Fj; Lopez, Jj; De la Morena, J; Crialesi-Esposito, M
abstract

Nozzle hydraulic performance has a significant impact on diesel spray development and combustion characteristics. Thus, it is important to understand the links between the nozzle geometry, the internal flow features and the spray formation. In this paper, a detailed analysis of the impact of the nozzle orifices inclination angle on its hydraulic performance is performed. For this purpose, three different nozzles with included angles of 90, 140 and 155 degrees are evaluated. Instantaneous injection rate and momentum flux are measured on a set of injector operating conditions (mainly injection pressure and discharge pressure). The results show that higher inclination angles lead to smaller mass flow and momentum flux at steady-state conditions, due to the higher losses at the orifice inlet. These losses are translated in lower both area and velocity coefficients. Nevertheless, the impact of this parameter is limited thanks to the counter-acting effect of the hydrogrinding process, which produces larger rounding radii at the orifice inlet as the included angle increases. Based on the experimental results, correlations of the discharge coefficient as a function of the Reynolds number are obtained and evaluated. (C) 2017 Elsevier Ltd. All rights reserved.

2017 - Experimental assessment of the fuel heating and the validity of the assumption of adiabatic flow through the internal orifices of a diesel injector [Articolo su rivista]
Salvador, F. J.; Gimeno, J.; Carreres, M.; Crialesi-Esposito, M.
abstract

In this paper an experimental investigation on the heating experienced by the fuel when it expands through the calibrated orifices of a diesel injector is carried out. Five different geometries corresponding to the control orifices of two different commercial common-rail solenoid injectors were tested. An experimental facility was used to impose a continuous flow through the orifices by controlling the pressures both upstream and downstream of the restriction. Fuel temperature was controlled prior to the orifice inlet and measured after the outlet at a location where the flow is already slowed down. Results were compared to the theoretical temperature increase under the assumption of adiabatic flow (i.e. isenthalpic process). The comparison points out that this assumption allows to predict the fuel temperature change in a reasonable way for four of the five geometries as long as the pressure difference across the orifice is high enough. The deviations for low imposed pressure differences and the remaining orifice are explained due to the low Reynolds numbers (i.e. flow velocities) induced in these cases, which significantly increase the residence time of a fuel particle in the duct, thus enabling heat transfer with the surrounding atmosphere. A dimensionless parameter to quantify the proneness of the flow through an orifice to exchange heat with the surroundings has been theoretically derived and calculated for the different geometries tested, allowing to establish a boundary that defines beforehand the conditions from which heat losses to the ambient can be neglected when dealing with the internal flow along a diesel injector. (C) 2016 Elsevier Ltd. All rights reserved.

2016 - Fuel temperature influence on the performance of a last generation common-rail diesel ballistic injector. Part I: Experimental mass flow rate measurements and discussion [Articolo su rivista]
Salvador, Fj; Gimeno, J; Carreres, M; Crialesi-Esposito, M
abstract

An experimental study is conducted in this paper in order to assess the influence of the fuel temperature on the performance of a last generation common-rail ballistic solenoid injector. Mass flow rate measurements are performed for a wide range of temperatures, extending from 253 to 373 K, representative of all the possible operating conditions of the injector in a real diesel engine, including cold start. The high pressure line and the injector holder were refrigerated, making it possible to carefully control the fuel temperature, whereas measurements at cold conditions were carried out with the help of a climatic chamber. Relevant features such as stationary mass flow, injection delay or the behaviour at the opening and closing stages are analysed together with parameters governing the flow, such as the injector discharge coefficient.Results show an important influence of the fuel temperature, especially at low injection pressure. A low injection temperature results in a lower stationary mass flow rate, whereas injection duration is also reduced. These results will be explained mainly through the fuel properties variation induced by temperature, together with the ballistic nature of the injector used for the study.A second part of the paper introduces a one-dimensional model that makes it possible to reproduce these results and further explain them through the analysis of other relevant variables, such as the needle lift. (C) 2016 Elsevier Ltd. All rights reserved.

2015 - Nonlinear model predictive control of an Organic Rankine Cycle for exhaust waste heat recovery in automotive engines [Relazione in Atti di Convegno]
Esposito, M. C.; Pompini, N.; Gambarotta, A.; Chandrasekaran, V.; Zhou, J.; Canova, M.
abstract

Energy recovery from exhaust gas waste heat can be regarded as an effective way to improve the energy efficiency of automotive powertrains, thus reducing CO2 emissions. The application of Organic Rankine Cycles (ORCs) to waste heat recovery is a solution that couples effectiveness and reasonably low technological risks. On the other hand, ORC plants are rather complex to design, integrate and control, due to the presence of heat exchangers operating with phase changing fluid, and several control devices to regulate the thermodynamic states of the systems. Furthermore, the power output and efficiency of ORC systems are extremely sensitive to the operating conditions, requiring precise control of the evaporator pressure and superheat temperature. This paper presents an optimization and control design study for an Organic Rankine Cycle plant for automotive engine waste heat recovery. The analysis has been developed using a detailed Moving Boundary Model that predicts mass and energy flows through the heat exchangers, valves, pumps and expander, as well as the system performance. Starting from the model results, a nonlinear model predictive controller is designed to optimize the transient response of the ORC system. Simulation results for an acceleration-deceleration test illustrate the benefits of the proposed control strategy.