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http://hdl.handle.net/10985/8680
Wind-tunnel pressure measurements on model-scale rigid downwind sails
BOT, Patrick; MARIA VIOLA, Ignazio; FLAY, Richard G.J.; BRETT, Jean-Sebastien
This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubble, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot. Analysis of pressure time histories allows the large scale vortex shedding to be detected in the separation region, with a Strouhal number in the range 0.1 – 0.3, based on local sail chord length.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/86802014-01-01T00:00:00ZBOT, PatrickMARIA VIOLA, IgnazioFLAY, Richard G.J.BRETT, Jean-SebastienThis paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubble, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot. Analysis of pressure time histories allows the large scale vortex shedding to be detected in the separation region, with a Strouhal number in the range 0.1 – 0.3, based on local sail chord length.Sharp Transition in the Lift Force of a Fluid Flowing Past Nonsymmetrical Obstacles: Evidence for a Lift Crisis in the Drag Crisis Regime
http://hdl.handle.net/10985/11396
Sharp Transition in the Lift Force of a Fluid Flowing Past Nonsymmetrical Obstacles: Evidence for a Lift Crisis in the Drag Crisis Regime
BOT, Patrick; RABAUD, Marc; THOMAS, Goulven; LOMBARDI, Alessandro; LEBRET, Charles
Bluff bodies moving in a fluid experience a drag force which usually increases with velocity. However in a particular velocity range a drag crisis is observed, i.e., a sharp and strong decrease of the drag force. This counterintuitive result is well characterized for a sphere or a cylinder. Here we show that, for an object breaking the up-down symmetry, a lift crisis is observed simultaneously to the drag crisis. The term lift crisis refers to the fact that at constant incidence the time-averaged transverse force, which remains small or even negative at low velocity, transitions abruptly to large positive values above a critical flow velocity. This transition is characterized from direct force measurements as well as from change in the velocity field around the obstacle.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/113962016-01-01T00:00:00ZBOT, PatrickRABAUD, MarcTHOMAS, GoulvenLOMBARDI, AlessandroLEBRET, CharlesBluff bodies moving in a fluid experience a drag force which usually increases with velocity. However in a particular velocity range a drag crisis is observed, i.e., a sharp and strong decrease of the drag force. This counterintuitive result is well characterized for a sphere or a cylinder. Here we show that, for an object breaking the up-down symmetry, a lift crisis is observed simultaneously to the drag crisis. The term lift crisis refers to the fact that at constant incidence the time-averaged transverse force, which remains small or even negative at low velocity, transitions abruptly to large positive values above a critical flow velocity. This transition is characterized from direct force measurements as well as from change in the velocity field around the obstacle.Discontinuity of lift on a hydrofoil in reversed flow for tidal turbine Application
http://hdl.handle.net/10985/12715
Discontinuity of lift on a hydrofoil in reversed flow for tidal turbine Application
MARCHAND, Jean-Baptiste; ASTOLFI, Jacques Andre; BOT, Patrick
This work presents an experimental investigation of a hydrofoil in reversed flow configuration in the context of marine current turbine development. Experiments consist in hydrodynamic force measurements and PIV flow observations on a NACA 0015 hydrofoil, at 5 × 105 Reynolds number. The hydrofoil in reversed flow produces a higher lift than in the classical forward flow for very low angles of attack and proved to be relatively efficient for an angle of attack lower than 10°, despite a much higher drag than the same foil in direct flow. Moreover, the lift coefficient shows a discontinuity with an hysteresis effect when the angle of attack is varied up and down around zero-degree. It is shown that the sharp leading edge generates an early Leading Edge Separation Bubble on one side (suction side) even for vanishing angles of attack. This separation bubble triggers the transition to turbulence of the boundary layer on the suction side while the pressure side boundary layer remains laminar. As a consequence, separation on the rounded trailing edge occurs farther downstream on the (turbulent) suction side compared to the (laminar) pressure side. The Leading Edge Separation Bubble and the inherent up–down asymmetry in the boundary layer regime are responsible for the lift singularity.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/127152017-01-01T00:00:00ZMARCHAND, Jean-BaptisteASTOLFI, Jacques AndreBOT, PatrickThis work presents an experimental investigation of a hydrofoil in reversed flow configuration in the context of marine current turbine development. Experiments consist in hydrodynamic force measurements and PIV flow observations on a NACA 0015 hydrofoil, at 5 × 105 Reynolds number. The hydrofoil in reversed flow produces a higher lift than in the classical forward flow for very low angles of attack and proved to be relatively efficient for an angle of attack lower than 10°, despite a much higher drag than the same foil in direct flow. Moreover, the lift coefficient shows a discontinuity with an hysteresis effect when the angle of attack is varied up and down around zero-degree. It is shown that the sharp leading edge generates an early Leading Edge Separation Bubble on one side (suction side) even for vanishing angles of attack. This separation bubble triggers the transition to turbulence of the boundary layer on the suction side while the pressure side boundary layer remains laminar. As a consequence, separation on the rounded trailing edge occurs farther downstream on the (turbulent) suction side compared to the (laminar) pressure side. The Leading Edge Separation Bubble and the inherent up–down asymmetry in the boundary layer regime are responsible for the lift singularity.Fluid Structure Interaction of Yacht Sails in the Unsteady Regime
http://hdl.handle.net/10985/12555
Fluid Structure Interaction of Yacht Sails in the Unsteady Regime
AUGIER, Benoit; BOT, Patrick; HAUVILLE, Frédéric; DURAND, Mathieu
The dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillate with phase shifts with respect to the motion. This results in hysteresis phenomena, which show aerodynamic equivalent damping and stiffening effects of the unsteady behaviour. The area of the hysteresis loop corresponds to the amount of energy exchanged by the system and increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/125552013-01-01T00:00:00ZAUGIER, BenoitBOT, PatrickHAUVILLE, FrédéricDURAND, MathieuThe dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillate with phase shifts with respect to the motion. This results in hysteresis phenomena, which show aerodynamic equivalent damping and stiffening effects of the unsteady behaviour. The area of the hysteresis loop corresponds to the amount of energy exchanged by the system and increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure.Numerical study of a Flexible Sail Plan submitted to pitching : Hysteresis phenomenon and effect of rig Adjustments
http://hdl.handle.net/10985/8688
Numerical study of a Flexible Sail Plan submitted to pitching : Hysteresis phenomenon and effect of rig Adjustments
AUGIER, Benoit; HAUVILLE, Frédéric; BOT, Patrick; AUBIN, Nicolas; DURAND, Mathieu
A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to analyse the system's dynamic behaviour and the effects of motion simplifications and rigging adjustments on aerodynamic forces. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops. It is shown that the hysteresis phenomenon dissipates some energy and that the dissipated energy increases strongly with the pitching reduced frequency and amplitude. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies with underestimated aerodynamic forces and no more hysteresis when a surge motion is considered. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan. The energy dissipated by the hysteresis is higher for looser shrouds and a tighter backstay.
Yacht sails dynamic fluid structure interaction is simulated in harmonic pitching Aerodynamic forces show hysteresis associated to energy dissipation Dissipated energy increases with pitching frequency and amplitude Hysteresis is cancelled and forces underestimated when motion is reduced to surge Looser shrouds and tighter backstay increase dissipated energy
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/86882014-01-01T00:00:00ZAUGIER, BenoitHAUVILLE, FrédéricBOT, PatrickAUBIN, NicolasDURAND, MathieuA numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to analyse the system's dynamic behaviour and the effects of motion simplifications and rigging adjustments on aerodynamic forces. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops. It is shown that the hysteresis phenomenon dissipates some energy and that the dissipated energy increases strongly with the pitching reduced frequency and amplitude. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies with underestimated aerodynamic forces and no more hysteresis when a surge motion is considered. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan. The energy dissipated by the hysteresis is higher for looser shrouds and a tighter backstay.Fluid Structure Interaction of Yacht Sails in the Unsteady Regime
http://hdl.handle.net/10985/9089
Fluid Structure Interaction of Yacht Sails in the Unsteady Regime
AUGIER, Benoit; BOT, Patrick; HAUVILLE, Frédéric; DURAND, Mathieu
The dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillation shows hysteresis phenomena and equivalent damping and stiffening effects of the unsteady beahvior. The area of the hysteresis loop increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/90892013-01-01T00:00:00ZAUGIER, BenoitBOT, PatrickHAUVILLE, FrédéricDURAND, MathieuThe dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillation shows hysteresis phenomena and equivalent damping and stiffening effects of the unsteady beahvior. The area of the hysteresis loop increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure.Full-scale flying shape measurement of offwind yacht sails with photogrammetry
http://hdl.handle.net/10985/11250
Full-scale flying shape measurement of offwind yacht sails with photogrammetry
DEPARDAY, Julien; BOT, Patrick; HAUVILLE, Frédéric; AUGIER, Benoit; RABAUD, Marc
Yacht downwind sails are complex to study due to their non-developable shape with high camber and massively detached flow around thin and flexible membranes. Numerical simulations can now simulate this strong fluid-structure interaction, but need experimental validation. It remains complex to measure spinnaker flying shapes partly because of their inherent instability, like luff flapping. This work presents full-scale experimental investigation of spinnaker shapes with simultaneous measurement of aerodynamic loads on the three sail corners, with navigation and wind data. The experimental set-up and photogrammetric method are presented. Results are analysed in the whole range of apparent wind angle for this sail. The spinnaker shape shows dramatic variations and high discrepancies with the design shape. The photogrammetric measurement produces the full 3D flying shape with a satisfactory accuracy. Even if only steady state results are given here, this new system enables time-resolved measurement of flying shapes and thus flapping of spinnakers to be investigated, which is valuable for yacht performance optimisation. On top of sailing yacht applications, the method is useful in any application where a non-developable 3D shape is to be determined, and particularly when it results from the Fluid Structure Interaction of a flexible structure with a complex flow.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/112502016-01-01T00:00:00ZDEPARDAY, JulienBOT, PatrickHAUVILLE, FrédéricAUGIER, BenoitRABAUD, MarcYacht downwind sails are complex to study due to their non-developable shape with high camber and massively detached flow around thin and flexible membranes. Numerical simulations can now simulate this strong fluid-structure interaction, but need experimental validation. It remains complex to measure spinnaker flying shapes partly because of their inherent instability, like luff flapping. This work presents full-scale experimental investigation of spinnaker shapes with simultaneous measurement of aerodynamic loads on the three sail corners, with navigation and wind data. The experimental set-up and photogrammetric method are presented. Results are analysed in the whole range of apparent wind angle for this sail. The spinnaker shape shows dramatic variations and high discrepancies with the design shape. The photogrammetric measurement produces the full 3D flying shape with a satisfactory accuracy. Even if only steady state results are given here, this new system enables time-resolved measurement of flying shapes and thus flapping of spinnakers to be investigated, which is valuable for yacht performance optimisation. On top of sailing yacht applications, the method is useful in any application where a non-developable 3D shape is to be determined, and particularly when it results from the Fluid Structure Interaction of a flexible structure with a complex flow.Wind-tunnel pressure measurements on model-scale rigid downwind sails
http://hdl.handle.net/10985/14915
Wind-tunnel pressure measurements on model-scale rigid downwind sails
BOT, Patrick; MARIA VIOLA, Ignazio; FLAY, Richard G.J.; BRETT, Jean-Sébastien
This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubbles, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/149152013-01-01T00:00:00ZBOT, PatrickMARIA VIOLA, IgnazioFLAY, Richard G.J.BRETT, Jean-SébastienThis paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubbles, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot.Experimental Study of the Flow in a Compact Heat Exchanger Channel with Embossed-type Vortex Generators
http://hdl.handle.net/10985/9495
Experimental Study of the Flow in a Compact Heat Exchanger Channel with Embossed-type Vortex Generators
DUPONT, Frédéric; GABILLET, Céline; BOT, Patrick
The isothermal flow in a model channel of plate-fin heat exchanger with periodically arranged embossed-like vortex generators is investigated. Velocity measurements are performed by LDA in the transitional regime (Reynolds number from 1000 up to 5000). Strong longitudinal vortices are observed downstream of each vortex generator. The vortex roll-up process is highlighted by the evolution of the velocity vector field in the cross section of the flow. The modifications of the vortex characteristics after successively encountered generators are investigated. This work shows most of the flow features which are known to produce heat transfer enhancement, and shows that these smooth shaped vortex generators are very promising for enhanced heat exchangers.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10985/94952003-01-01T00:00:00ZDUPONT, FrédéricGABILLET, CélineBOT, PatrickThe isothermal flow in a model channel of plate-fin heat exchanger with periodically arranged embossed-like vortex generators is investigated. Velocity measurements are performed by LDA in the transitional regime (Reynolds number from 1000 up to 5000). Strong longitudinal vortices are observed downstream of each vortex generator. The vortex roll-up process is highlighted by the evolution of the velocity vector field in the cross section of the flow. The modifications of the vortex characteristics after successively encountered generators are investigated. This work shows most of the flow features which are known to produce heat transfer enhancement, and shows that these smooth shaped vortex generators are very promising for enhanced heat exchangers.Transducteur adapté à la génération de forces en fonction de la vitesse d'écoulement d'un fluide
http://hdl.handle.net/10985/12674
Transducteur adapté à la génération de forces en fonction de la vitesse d'écoulement d'un fluide
BOT, Patrick
L’invention concerne un dispositif détecteur d’une vitesse seuil de déplacement d’un fluide, le dispositif détecteur comprenant un transducteur et configuré pour exercer une première force non nulle dans une première direction lorsque la vitesse du fluide est inférieure à la vitesse seuil et pour exercer une seconde force non nulle dans une seconde direction lorsque la vitesse du fluide est supérieure à la vitesse seuil , la première et la seconde direction étant identiques ou sensiblement identiques et la première et la deuxième force étant dirigées dans des sens opposés.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/126742017-01-01T00:00:00ZBOT, PatrickL’invention concerne un dispositif détecteur d’une vitesse seuil de déplacement d’un fluide, le dispositif détecteur comprenant un transducteur et configuré pour exercer une première force non nulle dans une première direction lorsque la vitesse du fluide est inférieure à la vitesse seuil et pour exercer une seconde force non nulle dans une seconde direction lorsque la vitesse du fluide est supérieure à la vitesse seuil , la première et la seconde direction étant identiques ou sensiblement identiques et la première et la deuxième force étant dirigées dans des sens opposés.