L'evoluzione delle tecniche sperimentali nell'idrodinamica navale Particle Image Velocimetry, potenzialità, criticità ed applicazioni

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1 L'evoluzione delle tecniche sperimentali nell'idrodinamica navale Particle Image Velocimetry, potenzialità, criticità ed applicazioni Massimo Falchi, Mario Felli, Giovanni Aloisio, Silvano Grizzi, Fabio Di Felice

2 Outline Focus on the velocity measurements Techniques, pros and cons Particle image velocimetry - PIV Working principle The stereoscopic approach - The Stereo PIV Applications of naval interests Propeller-rudder interaction DELFT Catamaran in steady drift The tomographic approach - The Tomo-PIV Investigation on the wake of a naval propeller Limits and future applications

3 Measuring techniques for the velocity field Point-like, low spatial resolution, low frequency acquisition Pitot tube easy to perform low information very low cost intrusive Point-like, high spatial resolution, high frequency acquisition medium difficulty easy to damage Hot wire/film anemometry turbulence investigation intrusive low cost Laser Doppler anemometry Point-like, high spatial resolution, high frequency acquisition robust non intrusive requires calibration turbulence investigation expensive Particle Image velocimetry Intrinsecally planar, high spatial resolution, low/high frequency acquisition INTRINSECALLY PLANAR!! Instantaneous vortex topology, velocity gradients and spatial correlations

4 PIV and Stereo-PIV working principle (a) (a) (b) (c) 2D Piv working principle 2D out-of-plane error Angular stereo set-up (b) (c)

5 PIV and Stereo-PIV working principle designed by INSEAN-CNR, realized by TSI

6 PIV and Stereo-PIV working principle

7 PIV and Stereo-PIV working principle Camera C Camera B Laser Camera A Asymmetric configuration Symmetric configuration

8 Applications Propeller-rudder interaction DELFT Catamaran in steady drift Investigation on the wake of a naval propeller by Tomo-PIV

9 Propeller-rudder interaction supported by supported by the Italian Ministry of Defence in the framework of the research project PRIAMO, PNRM Felli M, Falchi M, PROPELLER TIP AND HUB VORTEX DYNAMICS IN THE INTERACTION WITH A RUDDER, Experiments in Fluids, Vol. 51, Issue 5, pp

10 Set-up and test matrix Vector grid 1.25 mm

11 Vorticity These are NOT simulations!!

12 Vortex breakdown

13 Applications Propeller-rudder interaction DELFT Catamaran in steady drift Investigation on the wake of a naval propeller by Tomo-PIV

14 DELFT Catamaran in steady drift NICOP project ''Complementary EFD and CFD Analysis of Calm Water Hydrodynamics and Large Amplitude Motion for High-Speed Catamarans', founded by the U.S. Office of Naval Research (ONR). In collaboration with, The University of Iowa, Iowa City, USA. Broglia R, Aloisio G, Falchi M, Grizzi S, Zaghi S, Felli M, Miozzi M, Pereira F, Di Felice F and Stern F, MEASUREMENTS OF THE VELOCITY FIELD AROUND THE DELFT 372 CATAMARAN IN STEADY DRIFT, Proceedings of the 29 th ONR Symposium on Naval Hydrodynamics Gothenburg, Sweden, 26-31August Falchi M, Felli M, Grizzi S, Aloisio G, Broglia R and Stern F, SPIV MEASUREMENTS AROUND THE DELFT 372 CATAMARAN IN STEADY DRIFT, Experiments in Fluids, 2014, Vol. 55, Issue 11, article number 1844.

15 Vorticity Fr=0.4 =6

16 Bilge vortex features Roll up of the hull boundary layer Vorticity snapshot Average over 500 images

17 Bilge vortex intensity Γ = ds The strength of the keel vortices is larger in the leeward demihull and tends to increase as the Froude number reduces and the drift angle increases. The strength ratio between the windward and the leeward vortices ranges from 0.80 to th INTERNATIONAL SYMPOSIUM ON PARTICLE IMAGE VELOCIMETRY PIV13 Delft, The Netherlands, July 1-3, 2013

18 Vorticity fluctuations Fr=0.4 =6 Fr=0.5 =6

19 Vorticity fluctuations Dramatic reduction of vorticity fluctuations (about 40% from 0.7L pp to 1.15L pp ) Increase of vorticity fluctuations Effect of turbulent diffusion Incoming Destabilization? Free surface Effects?

20 Applications Propeller-rudder interaction DELFT Catamaran in steady drift Investigation on the wake of a naval propeller by Tomo-PIV

21 Tomo-PIV: Investigation on the wake of a naval propeller supported by the Italian Ministry of Education, University and Research in the framework of the research project RITMARE, coordinated by CNR Felli M, Falchi M, Dubbioso G, EXPERIMENTAL APPROACHES FOR THE DIAGNOSTICS OF HYDROACOUSTIC PROBLEMS IN NAVAL PROPULSION, 2015, Ocean Engineering 106, 1-19 Felli M, Falchi M, Dubbioso G, TOMOGRAPHIC-PIV SURVEY OF THE NEAR-FIELD HYDRODYNAMIC AND HYDROACOUSTIC CHARACTERISTICS OF A MARINE PROPELLER, 2015, Journal of Ship Research 59 (4),

22 Tomographic reconstruction Propellers as a reliable and efficient tool to generate thrust in aeronautical and marine propulsion systems. The comprehension about the hydrodynamic phenomena is still incomplete and a number of questions still open. The flow in the wake of a marine propeller is characterized by complex unsteady three-dimensional coherent structures generated at the blades and the hub that, mutually interacting, are destabilized and destroyed far downstream. Tomo-PIV represents a well assessed and attractive tool for the investigation of fully three dimensional turbulent and unsteady flows, such as the wake of a propeller.

23 Tomographic approach

24 Vorticity fluctuations

25 Vorticity field Felli et al., Mechanisms of evolution of the propeller wake in the transition and far fields, Journal of Fluid Mechanics, 2011 Tip vortex pairing

26 Vorticity - near field

27 Limits and future applications Limits Free surface Reflections at air-water interface, Air entrapment and air bubbles due to wave breaking Absence or reduction of the opical access Future applications Models in manouvres (PMM) Models in waves (PMM) Off design conditions Tomo-PIV investigations on skewed propellers

28 Thank you