Papers by Giovanni Aloisio
Journal of Physics: Conference Series
Currently, several countries already invest on the application of drones for different scopes. Th... more Currently, several countries already invest on the application of drones for different scopes. These purposes are mainly civilian and military and some of these include the presence of water as search and rescue, inspection of pipelines, getting a bird’s eyes view over oil spills or structural integrity monitoring of bridges. For this reason, an interesting feature for drones is their ability to maneuver in fluids with different density as air and water. This research topic, shows strong scientific potentiality but it also represents a great challenge from scientific and technical view point: i) aeronautical propeller for drones in water must generate reverse thrust or braking force through an off-design rotation in off-design condition (different fluid’s density); ii) the propeller rotational velocity in water is generally one order of magnitude lower than the one for air application requiring the motors to be properly desing to meet such a wide operational range. In this paper, an...
Day 1 Tue, September 12, 2006, 2006
In the present study an experimental analysis of the propeller-rudder interaction has been perfor... more In the present study an experimental analysis of the propeller-rudder interaction has been performed in a cavitation tunnel. The experiments simulated the condition of a rudder operation aft of a propeller but without the influence of the hull. The activity has been performed through dynamometric measurements, LDV phase sampling techniques and flow visualizations with an high speed camera.
Nowadays Stereo-PIV (SPIV) technique has reached a level of accuracy and precision suitable to a ... more Nowadays Stereo-PIV (SPIV) technique has reached a level of accuracy and precision suitable to a wide use in industrial facilities. Nonetheless, performing Stereo-PIV measurements in large hydrodynamic facilities for naval applications-e.g. large cavitation tunnels, towing tanks, maneuverability basins-still poses challenging operative, technical and theoretical problems; in these regards, solutions are required to assure good quality results when dealing with deep underwater conditions, reflections from the hull model, bubbly and two-phase flows, air-water interface and air bubbles entrapment by breaking waves, to name a few. In the present work, an underwater modular probe is introduced, designed to host all the electronic and optic hardware required to perform 3C-2D velocity measurements around surface and submersible models. In particular, an application to a test case is presented; a catamaran model advancing in steady drift at different angles and velocities is investigated to study the dynamics of the keel vortices generated along the demi-hulls and their interaction with the free surface.
This paper presents the ongoing experimental and numerical investigations on the hydrodynamic pe... more This paper presents the ongoing experimental and numerical investigations on the hydrodynamic performance of a high-speed catamaran model. This catamaran is a Delft model 372, designed and already tested at the Technical University of Delft; the main features are reported in Figure 1. The work has been done in the framework of a NICOP collaboration project between the Istituto Nazionale per Studi ed Esperienze di Architettura Navale (CNR-INSEAN) and the Iowa Institute of Hydraulic Research (IIHR). The focus is on the characterization of the hydrodynamic behavior of the catamaran advancing in steady drift by means of a combined experimental and numerical activities. In particular, the aim of the present study is two-fold: to investigate the effects of drift angle on the flow field of a multi-hull vessel, with emphasis on the strong vortical structures generated along the keel of each demi-hull and to provide a valuable data base for CFD benchmarking. To these aims, experimental Stereo-PIV measurements have been provided for different drift angles and on several cross planes; velocity measurements have been acquired in the region between the demi-hulls, as well as on the external region of the leeward hull by using the CNR-INSEAN underwater stereo PIV system [1], Figure 2. In addition, resistance, lateral force and yaw moment have been measured. A numerical simulation campaign have been carried out at the same test conditions of the velocity measurements. Numerical simulations have been conducted using an home-developed code, χnavis [2], [3]. Preliminary simulations have been already performed on a grid not refined enough to capture the vortical structure detached from the hull surface. Nevertheless, from these simulations a rough idea of the main features of the flow field around the catamaran advancing in steady drift can be observed in Figure 3.
The 31st International Ocean and Polar Engineering Conference, Jun 20, 2021
The results of an experimental analysis of the velocity field around a ship model in forced roll ... more The results of an experimental analysis of the velocity field around a ship model in forced roll motion are presented. Tests, carried out at the INSEAN towing tank n° 2, aim to achieve a better physical understanding of the fluid dynamics and a certified experimental data set for CFD validation. Results describe the evolution of the flow field in two cross sections along the bilge keels during damped roll motion. A PIV algorithm based on window deformation is used to improve the estimate of the vorticity. The mean unsteady flow field is obtained by ensemble averaging of time histories. The hydrodynamic damping effectiveness of the bilge keels is highlighted by the generation of strong vortical structures that characterize the transfer of energy between the hull and the surrounding flow field.
This work presents the results of an experimental campaign aimed at evaluating improvements in th... more This work presents the results of an experimental campaign aimed at evaluating improvements in the hydrodynamic performance of the state-of-art single screw propeller ship. In particular, the effect on introducing appendages to modify the hull boundary layer incoming to the propeller plane is here addressed. Two layouts of vortex generators, characterized by fins in the same position but at different inclination, 25.6° and 7.6° angle degrees with respect to the waterline, have been investigated; to study the effects of such devices, a stereoscopic PIV measurement campaign on a tanker scale model, λ = 16.5, has been performed at the selected speed of 14 knots. For all the studied conditions, the distribution of the mean velocity components, vorticity fields and statistical data have been calculated.
Springer Proceedings Physics
This work describes an experimental study of the flow field and wall pressure fluctuations induce... more This work describes an experimental study of the flow field and wall pressure fluctuations induced by quasi-twodimensional incompressible turbulent boundary layers overflowing a forward-facing step (FFS). Pressure fluctuations are measured upstream and downstream an instrumented FFS step model installed inside a large-scale recirculation water tunnel while two dimensional velocity fields are measured close to the step via time-resolved PIV. The overall flow physics is studied in terms of averaged velocity and vorticity fields for different Reynolds number based on the step's height. Pressure spectra and cross-correlations are measured as well, and the convection velocity characterizing the propagation of acoustic and hydrodynamic perturbations is computed as a function of the distance from the vertical side of the step. The evolution of the overall Sound Pressure Level measured at the wall shows that the most critical flow structure is the reattachment region downstream the step where an unsteady recirculation bubble is formed.
Journal of Turbulence, 2009
In this work, time-resolved two-dimensional particle image velocimetry measurements in a zero pre... more In this work, time-resolved two-dimensional particle image velocimetry measurements in a zero pressure gradient turbulent boundary layer at high Reynolds numbers (Reθ = 3940 and 7257, based on momentum thickness) are presented. The boundary layer is obtained on the flat wall of a very large recirculating water channel and is investigated on a streamwise–wall-normal plane. Statistical moments of velocity are
ABSTRACT The present work concerns the experimental measurements of the velocity field around a c... more ABSTRACT The present work concerns the experimental measurements of the velocity field around a catamaran advancing in static drift. The main aim of the paper was to investigate the dynamics of the vortices generated by catamaran hulls with particular emphasis on the mechanisms of generation, detachment, downstream evolution and destabilization. In this context, a Stereo-PIV campaign has been performed to map the velocity fields on some cross-planes along and downstream of the catamaran. Froude numbers equal to 0.4 and 0.5 at drift angles as large as 6 degrees and 9 degrees have been selected as testing conditions. In all the tests, the model has been fixed at the dynamical values of trim and sinkage, measured in a preliminary static drift experiments. Major geometrical and kinematical characteristics of the keel vortices have been documented in the paper through the analysis of the mean and fluctuating components of the velocity and vorticity field. Vortex interaction with the wave pattern has been investigated as well through the use of a conditional average technique of the velocity snapshots with the free surface elevation. As a secondary, but important, outcome, a valuable experimental dataset for CFD benchmarking in severe off-design conditions has been collected.
Springer Proceedings Physics, 2007
This work describes an experimental study of the flow field and wall pressure fluctuations induce... more This work describes an experimental study of the flow field and wall pressure fluctuations induced by quasi-twodimensional incompressible turbulent boundary layers overflowing a forward-facing step (FFS). Pressure fluctuations are measured upstream and downstream an instrumented FFS step model installed inside a large-scale recirculation water tunnel while two dimensional velocity fields are measured close to the step via time-resolved PIV. The overall flow physics is studied in terms of averaged velocity and vorticity fields for different Reynolds number based on the step's height. Pressure spectra and cross-correlations are measured as well, and the convection velocity characterizing the propagation of acoustic and hydrodynamic perturbations is computed as a function of the distance from the vertical side of the step. The evolution of the overall Sound Pressure Level measured at the wall shows that the most critical flow structure is the reattachment region downstream the step where an unsteady recirculation bubble is formed.
Physics of Fluids, 2008
This work describes an experimental study of the flow field and wall pressure fluctuations induce... more This work describes an experimental study of the flow field and wall pressure fluctuations induced by quasi-two-dimensional incompressible turbulent boundary layers overflowing a forward-facing step (FFS). Pressure fluctuations are measured upstream and downstream of an instrumented FFS step model installed inside a large scale recirculation water tunnel, while two-dimensional (2D) velocity fields are measured close to the step via 2D
Journal of Turbulence, 2009
In this work, time-resolved two-dimensional particle image velocimetry measurements in a zero pre... more In this work, time-resolved two-dimensional particle image velocimetry measurements in a zero pressure gradient turbulent boundary layer at high Reynolds numbers (Reθ = 3940 and 7257, based on momentum thickness) are presented. The boundary layer is obtained on the flat wall of a very large recirculating water channel and is investigated on a streamwise–wall-normal plane. Statistical moments of velocity are
The results of an experimental analysis of the velocity field around a ship model in forced roll ... more The results of an experimental analysis of the velocity field around a ship model in forced roll motion are presented. Tests, carried out at the INSEAN towing tank n° 2, aim to achieve a better physical understanding of the fluid dynamics and a certified experimental data set for CFD validation. Results describe the evolution of the flow field in two cross sections along the bilge keels during damped roll motion. A PIV algorithm based on window deformation is used to improve the estimate of the vorticity. The mean unsteady flow field is obtained by ensemble averaging of time histories. The hydrodynamic damping effectiveness of the bilge keels is highlighted by the generation of strong vortical structures that characterize the transfer of energy between the hull and the surrounding flow field.
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Papers by Giovanni Aloisio