@article{
	11589_77183,
	author = { Fornarelli  F  and  Lippolis  A  and  Oresta  P },
	title = {Buoyancy effect on the flow pattern and the thermal performance of an array of circular cylinders},
	year = {9999},
	journal = {JOURNAL OF HEAT TRANSFER},
	abstract = {In this paper we found, by means of numerical simulations,
a transition in the oscillatory character of the flow field for a
particular combination of buoyancy and spacing in an array
of six circular cylinders at a Reynolds number of 100 and
Prandtl number of 0:7. The cylinders are iso-thermal and
they are aligned with the Earth acceleration (g). According
to the array orientation, an aiding or an opposing buoyancy
is considered. The effect of natural convection with respect
to the forced convection is modulated with the Richardson
number, Ri, ranging between 1 and 1. Two values of center
to center spacing (s = 3:6d 4d) are considered. The
effects of buoyancy and spacing on the flow pattern in the
near and far field are described. Several transitions in the
flow patterns are found and a parametric analysis of the dependence
of the force coefficients and Nusselt number with
respect to the Richardson number is reported. For Ri = 1,
the change of spacing ratio from 3:6 to 4 induces a transition
in the standard deviation of the force coefficients and
heat flux. In fact the transition occurs due to rearrangement
of the near field flow in a more ordered wake pattern. Therefore,
attention is focused on the influence of geometrical and
buoyancy parameters on the heat and momentum exchange
and their fluctuations. The available heat exchange models
for cylinders array provide a not accurate prediction of the
Nusselt number in the cases here studied.}
}
@article{
	11589_59941,
	author = { Fornarelli  F  and  Camporeale  S M  and  Fortunato  B  and  Torresi  M  and  Oresta  P  and  Magliocchetti  L  and  Miliozzi  A  and  Santo  G },
	title = {CFD analysis of melting process in a shell-and-tube latent heat storage for concentrated solar power plants},
	year = {2016},
	journal = {APPLIED ENERGY},
	volume = {164},
	abstract = {A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD simulations. This study aims at identifying the convective flows produced within the melted phase by temperature gradients and gravity. Simulations were carried out on experimental devices for applications to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat transfer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is examined by solving the unsteady Navier–Stokes equations for HTF and PCM and conduction for the tube. In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about 30% the time needed to charge the heat storage. A detailed description of the convective motion in the melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the mushy zone constant is also investigated.},
	keywords = {CFD; Thermal Energy Storage (TES); Phase Change Material (PCM); Molten salts; Shell and tube; Enthalpy-porosity model},
	doi = {10.1016/j.apenergy.2015.11.106},	
	pages = {711--722}
}
@article{
	11589_471,
	author = { Fornarelli F  and  Oresta P  and  Lippolis A },
	title = {Flow patterns and heat transfer around six in-line circular cylinders at low Reynolds number},
	year = {2015},
	journal = {JP JOURNAL OF HEAT AND MASS TRANSFER},
	volume = {11},
	abstract = {The flow field and the heat transfer around six in-line iso-thermal circular cylinders have been studied by means of numerical simulations. Two values of the center to center spacing \"\" and 4d, where dis the cylinder diameter) at Reynolds number of 100 and Prandtl number of 0.7 have been investigated. Similarly to the in-line two cylinders configuration, in this range, a transition in the flow and in the heat transfer occurs. Two different flow patterns have been identified: the stable shear layer (SSL) mode and the shear layer secondary vortices (SLSV) mode, at 3.6 and 4 spacing ratios respectively. At \"\" the flow pattern causes the entrainment of cold fluid on the downstream cylinders enhancing the heat transfer.  On the other hand, at \"\" two stable opposite shear layers prevent the cold fluid entrainment over the downstream cylinders reducing their heat exchange. The overall time average heat transfer of the array is enhanced up to 25% decreasing the spacing ratio from 4 to 3.6. Furthermore, it is found that the increased heat transfer is related to the phase shift between the Nusselt time series of successive cylinders.},
	keywords = {Forced convection; Low Reynolds number; DNS},
	url = {http://www.pphmj.com/abstract/8891.htm},
	doi = {http://dx.doi.org/10.17654/JPHMTFeb2015_001_028},	
	pages = {1--28}
}
@article{
	11589_8156,
	author = { Oresta P  and  Fornarelli F  and  and Prosperetti A },
	title = {Multiphase Rayleigh-Bénard convection},
	year = {2014},
	journal = {MECHANICAL ENGINEERING REVIEWS},
	volume = {1}
}
@conference{
	11589_21757,
	author = { Fornarelli F  and  Oresta P  and  Lippolis A },
	title = {Wake interference effects on the heat transfer enhancement around a row of circular cylinders},
	year = {2014},
	booktitle = {Proceedings of 10th European Fluid Mechanics Conference},
	abstract = {The numerical simulations of the heat transfer around an array of isothermal circular cylinders immersed in a
stream has been carried out solving the two-dimensional Navier-Stokes equations. The cylinders have been
placed in a single row configuration aligned with the free stream velocity at Reynolds number 100 and Prandtl
number 0.7.
In Fig.1 it is shown the instantaneous temperature distribution for the case of six in-line circular cylinders at
spacing ratio (s/d) equal to 4 and 3.6, where s is the center-to-center cylinder spacing and d is the cylinder
diameter.
In the latter case, a transition in the flow patterns occurs with the flow organized in a vortex shedding
responsible for the entrainment of cold fluid in the gaps. This phenomenon makes stronger the thermal gradient
close to the cylinders leading the heat transfer enhancement with the Nusselt number 25 % higher respect to the
case at s/d=4.
Furthermore a frequency analysis of the time dependent Nusselt number, Nui, at the i-th cylinder, shows that
the main frequency is the same for all the cylinders.
We found evidences that the signature of the heat transfer enhancement could be related to the phase shift
between two successive cylinders (i+1- i), where the phase shift (i) is defined as the difference between the
phase of each main harmonic component of the Nui respect to the phase of the signal at the first cylinder.}
}
@conference{
	11589_18430,
	author = { Fornarelli F  and  Oresta P  and  Lippolis A },
	title = {Flow transitions around in line cylinders},
	year = {2014},
	booktitle = {Proceedings of 1st  Workshop SCORE@POLIBA},
	abstract = {The flow around aligned cylinders is an archetype for several
industrial devices (rod structure of the nuclear reactors, compact heat
exchangers for electronic components, pin-fins heat exchangers for
micro-devices ) and environmental phenomena (diffusion process close to the
vegetation). Cylinders produce instabilities in the flow structures that are very
sensitive to the control parameters such as the inflow velocity, the spacing
between the cylinders and the fluid viscosity. The instabilities leads the
transport phenomena close to the cylinders and they affect the force, the
thermal balance at their surface and the diffusion process. The strong velocity
gradients in confined spaces make that the experimental analysis is difficult,
while the numerical simulation appears to be a promising tool for this purpose.},
	keywords = {Fluid dynamics; Bluff bodies; Wake interference}
}
@conference{
	11589_18396,
	author = { Fortunato B  and  Lippolis A  and  Vacca G  and  Amirante  R  and  Camporeale S M  and  Dambrosio  and  Oresta P  and  Torresi M  and  Fornarelli F },
	title = {Activities of the research group on  energy efficiency and renewable energy},
	year = {2014},
	publisher = {Gangemi},
	address = {ROMA},
	volume = {B},
	booktitle = {Groups mResearch on KERTS and SCS -
1st Workshop on the State of the Art and Challenges of Research Efforts of POLIBA},
	keywords = {Energy ; Renewable; Efficiency},
	pages = {173--177}
}
@article{
	11589_58717,
	author = { Mazzitelli  I M  and  Fornarelli  F  and  Lanotte  A S  and  Oresta  P },
	title = {Pair and multi-particle dispersion in numerical simulations of convective boundary layer turbulence},
	year = {2014},
	journal = {PHYSICS OF FLUIDS},
	volume = {26},
	keywords = {Condensed Matter Physics},
	url = {http://scitation.aip.org/content/aip/journal/pof2},
	doi = {10.1063/1.4878318},	
}
@article{
	11589_52143,
	author = { Posa A  and  Oresta P  and  Lippolis A },
	title = {Influence of the Spool Velocity on The Performance of a Directional Hydraulic Valve},
	year = {2013},
	journal = {INTERNATIONAL JOURNAL OF FLUID POWER},
	volume = {14},
	abstract = {In this paper an accurate numerical method has been used to verify the influence of the spool velocity on the performance
of a directional hydraulic valve (4/3, closed center): the flow during the opening phase of the valve has been
solved by Direct Numerical Simulation (DNS), using an Immersed-Boundary (IB) technique.
The present results have been compared with the ones of a previous study, based on the same numerical method, but
with a stationary spool. The numerical comparisons prove that the "quasi-stationary" hypothesis is approximately correct
for present commercial devices, but it is not suitable for future high-speed valves. However it is shown that, even
inside the range of the spool velocities currently adopted, for small pressure drops Δp and small openings s more significant
differences arise on the axial forces.},
	keywords = {Direct Numerical Simulation, Directional hydraulic valves, Finite-difference methods, Immersed-Boundary methods},
	doi = {10.1080/14399776.2013.10801410},	
	pages = {15--25}
}
@article{
	11589_8023,
	author = { Lakkaraju R  and  Stevens RJAM  and  Oresta P  and  Verzicco R  and  Lohse D  and  Prosperetti A },
	title = {Heat transport in bubbling turbulent convection},
	year = {2013},
	journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA},
	volume = {110},
	doi = {10.1073/pnas.1217546110},	
	pages = {9237--9242}
}
@article{
	11589_8098,
	author = { Oresta P  and  Prosperetti A },
	title = {Effects of particle settling on Rayleigh-Bénard convection},
	year = {2013},
	journal = {PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS},
	volume = {87},
	abstract = {The effect of particles falling under gravity in a weakly turbulent Rayleigh-B´enard gas flow is studied
numerically. The particle Stokes number is varied between 0.01 and 1 and their temperature is held fixed at
the temperature of the cold plate, of the hot plate, or the mean between these values. Mechanical, thermal, and
combined mechanical and thermal couplings between the particles and the fluid are studied separately. It is shown
that the mechanical coupling plays a greater and greater role in the increase of the Nusselt number with increasing
particle size. A rather unexpected result is an unusual kind of reverse one-way coupling, in the sense that the
fluid is found to be strongly influenced by the particles, while the particles themselves appear to be little affected
by the fluid, despite the relative smallness of the Stokes numbers. It is shown that this result derives from the
very strong constraint on the fluid behavior imposed by the vanishing of the mean fluid vertical velocity over the
cross sections of the cell demanded by continuity.},
	doi = {10.1103/PhysRevE.87.063014},	
	pages = {1--11}
}
@article{
	11589_1090,
	author = { Posa A  and  Oresta P  and  Lippolis A },
	title = {Analysis of a directional hydraulic valve by a direct numerical simulation
using an immersed-boundary method},
	year = {2013},
	journal = {ENERGY CONVERSION AND MANAGEMENT},
	volume = {65},
	abstract = {The improvement of the hydraulic valves depends on the careful analysis
of the coherent structures driving the motion of the working fluid. In the
past those devices have been studied by experimental tests; during the last
15 years also several numerical works have been presented, solving the flow
on body-fitted computational grids by RANS methods.
In this study a different approach is proposed for the axisymmetric analysis
of a directional valve (4/3, closed centre): whereas the RANS techniques are
based on the time-averaged equations of the flow, in the present work the unsteady Navier-Stokes equations have been solved using the Direct Numerical
Simulation (DNS); the time evolution of the physics is simulated, providing
important details on the instantaneous structures of the flow, affecting the valve performance. Furthermore, while in the previous numerical studies the
computational domain has been discretized by conformal grids, in this case
the fluid-body interaction has been represented by an immersed-boundary
(IB) method on a Cartesian grid, more suitable for unsteady eddy-resolving
simulations, as DNS.
The analysis of the discharge coefficient and the flow forces for different openings s and pressure drops ∆p is presented in this paper. The behaviour of
those global parameters is justified also considering the time-averaged and
the instantaneous fields. For small openings and pressure drops the flow is
steady and attached to the wall of the discharge chamber on the side of the
restricted section. When s and ∆p are increased the jet separates at the restricted section and it re-attaches downstream (Coanda effect), keeping the
steady state. Finally, for large openings and pressure drops the flow becomes
strongly unsteady: it is organized like a free jet and is dominated by large
vortices.},
	keywords = {Direct Numerical Simulation; Directional hydraulic valves; Immersed-Boundary methods},
	doi = {10.1016/j.enconman.2012.07.012},	
	pages = {497--506}
}
@conference{
	11589_25191,
	author = { Fornarelli F  and  Oresta P },
	title = {Flow field around an impinging droplets},
	year = {2012},
	booktitle = {European Fluid Mechanics Conference 9}
}
@article{
	11589_51933,
	author = { Posa A  and  Oresta P  and  Lippolis A },
	title = {Simulazione diretta del flusso in un distributore
oleodinamico mediante un metodo ai contorni immersi.
Direct Numerical Simulation on a directional hydraulic valve by an immersed-boundary method.},
	year = {2012},
	journal = {LA TERMOTECNICA},
	volume = {LXVI},
	abstract = {"In this paper a directional valve (4\/3, closed center) is analyzed using a code based on the immersed boundary method and solving the Navier-. Stokes equations by a Direct Numerical Simulation (DNS).. The results are presented in terms of instantaneous and time-averaged fields, showing the Coanda effect for small valve openings, and global parameters,. such as the discharge coefficient and the flow force coefficient K."},
	pages = {53--56}
}
@conference{
	11589_52601,
	author = { Rubino G  and  Fornarelli F  and  Lippolis A  and  Oresta P },
	title = {Fluid dynamic optimization of internal flow in a wind turbine nacelle},
	year = {2012},
	booktitle = {67° Congresso Nazionale ATI}
}