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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.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.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.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.On the Uncertainty of CFD in Sail Aerodynamics
http://hdl.handle.net/10985/8697
On the Uncertainty of CFD in Sail Aerodynamics
VIOLA, I.M; BOT, Patrick; RIOTTE, M.
A verification and validation procedure for yacht sail aerodynamics is presented. Guidelines and an example of application are provided. The grid uncertainty for the aerodynamic lift, drag and pressure distributions for the sails is computed. The pressures are validated against experimental measurements, showing that the validation procedure may allow the identification of modelling errors. Lift, drag and L2 norm of the pressures were computed with uncertainties of the order of 1%. Convergence uncertainty and round-off uncertainty are several orders of magnitude smaller than the grid uncertainty. The uncertainty due to the dimension of the computational domain is computed for a flat plate at incidence and is found to be significant compared with the other uncertainties. Finally, it is shown how the probability that the ranking between different geometries is correct can be estimated knowing the uncertainty in the computation of the value used to rank.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/86972013-01-01T00:00:00ZVIOLA, I.MBOT, PatrickRIOTTE, M.A verification and validation procedure for yacht sail aerodynamics is presented. Guidelines and an example of application are provided. The grid uncertainty for the aerodynamic lift, drag and pressure distributions for the sails is computed. The pressures are validated against experimental measurements, showing that the validation procedure may allow the identification of modelling errors. Lift, drag and L2 norm of the pressures were computed with uncertainties of the order of 1%. Convergence uncertainty and round-off uncertainty are several orders of magnitude smaller than the grid uncertainty. The uncertainty due to the dimension of the computational domain is computed for a flat plate at incidence and is found to be significant compared with the other uncertainties. Finally, it is shown how the probability that the ranking between different geometries is correct can be estimated knowing the uncertainty in the computation of the value used to rank.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.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.Upwind sail aerodynamics : A RANS numerical investigation validated with wind tunnel pressure measurements
http://hdl.handle.net/10985/8685
Upwind sail aerodynamics : A RANS numerical investigation validated with wind tunnel pressure measurements
BOT, Patrick
The aerodynamics of a sailing yacht with different sail trims are presented, derived from simulations performed using Computational Fluid Dynamics. A Reynolds-averaged Navier-Stokes approach was used to model sixteen sail trims first tested in a wind tunnel, where thepressure distributions on the sails were measured. An original approach was employed byusing two successive simulations: the first one on a large domain to model the blockage due to the wind tunnel walls and the sails model, and a second one on a smaller domain to model the flow around the sails model. A verification and validation of the computed aerodynamic forces and pressure distributions was performed. The computed pressure distribution is shown to agree well with the measured pressures. The sail surface pressure was correlated with the increase of turbulent viscosity in the laminar separation bubble, the flow reattachment and the trailing edge separation. The drive force distribution on both sails showed that the fore part of the genoa (fore sail) provides the majority of the drive force and that the effect of the aft sail is mostly to produce an upwash effect on the genoa. An aerodynamic model based on potential flow theory and a viscous correction is proposed. This model, with one free parameter to be determined, is shown to fit the results better than the usual form drag and induced drag only, even if no friction drag is explicitly considered.
A novel method similar to marching technique was used to model wind tunnel tests. ► Sail trim criteria based on their interactive effect are identified. ► Areas of separated flow were characterised. ► Local flow field was correlated with sail surface pressures. ► An aerodynamic model based on potential flow with viscous correction is proposed.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/86852012-01-01T00:00:00ZBOT, PatrickThe aerodynamics of a sailing yacht with different sail trims are presented, derived from simulations performed using Computational Fluid Dynamics. A Reynolds-averaged Navier-Stokes approach was used to model sixteen sail trims first tested in a wind tunnel, where thepressure distributions on the sails were measured. An original approach was employed byusing two successive simulations: the first one on a large domain to model the blockage due to the wind tunnel walls and the sails model, and a second one on a smaller domain to model the flow around the sails model. A verification and validation of the computed aerodynamic forces and pressure distributions was performed. The computed pressure distribution is shown to agree well with the measured pressures. The sail surface pressure was correlated with the increase of turbulent viscosity in the laminar separation bubble, the flow reattachment and the trailing edge separation. The drive force distribution on both sails showed that the fore part of the genoa (fore sail) provides the majority of the drive force and that the effect of the aft sail is mostly to produce an upwash effect on the genoa. An aerodynamic model based on potential flow theory and a viscous correction is proposed. This model, with one free parameter to be determined, is shown to fit the results better than the usual form drag and induced drag only, even if no friction drag is explicitly considered.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.Experimental validation of unsteady models for fluid structure interaction: Application to yacht sails and rigs
http://hdl.handle.net/10985/8692
Experimental validation of unsteady models for fluid structure interaction: Application to yacht sails and rigs
AUGIER, Benoit; BOT, Patrick; HAUVILLE, Frédéric; DURAND, Mathieu
This work presents a full scale experimental study on the aero-elastic wind/sails/rig interaction in real navigation conditions with the aim to give an experimental validation of unsteady fluid structure interaction (FSI) models applied to yacht sails. An inboard instrumentation system has been developed on a J80 yacht to simultaneously and dynamically measure the navigation parameters, yacht’s motion, and sails flying shape and loads in the standing and running rigging. The first results recorded while sailing upwind in head waves are shown. Variations of the measured parameters are characterized and related to the yacht motion (trim mainly). Correlations between the different parameters are examined. In the system’s response to the dynamic forcing (pitching motion) we attempt to distinguish between the aerodynamic effect of varying apparent wind induced by the motion and the structural effect of varying stresses and strains due to the motion and inertia. The dynamic full scale measurements presented underline the necessity of considering the unsteadiness of phenomena to correctly simulate a yacht’s behavior in actual sailing conditions. The simulation results from the FSI model compare very well with the experimental data for steady sailing conditions. For the unsteady conditions obtained in head waves, the first results show a good agreement between measurements and simulation.
• We present full scale measurements on a yacht sailing upwind in moderate head swell • We highlight the unsteadiness of the loads : peaks may be twice the mean value • The dynamic behavior differs from the steady state : hysteresis loop • Experimental results compare well with an original FSI model
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/86922012-01-01T00:00:00ZAUGIER, BenoitBOT, PatrickHAUVILLE, FrédéricDURAND, MathieuThis work presents a full scale experimental study on the aero-elastic wind/sails/rig interaction in real navigation conditions with the aim to give an experimental validation of unsteady fluid structure interaction (FSI) models applied to yacht sails. An inboard instrumentation system has been developed on a J80 yacht to simultaneously and dynamically measure the navigation parameters, yacht’s motion, and sails flying shape and loads in the standing and running rigging. The first results recorded while sailing upwind in head waves are shown. Variations of the measured parameters are characterized and related to the yacht motion (trim mainly). Correlations between the different parameters are examined. In the system’s response to the dynamic forcing (pitching motion) we attempt to distinguish between the aerodynamic effect of varying apparent wind induced by the motion and the structural effect of varying stresses and strains due to the motion and inertia. The dynamic full scale measurements presented underline the necessity of considering the unsteadiness of phenomena to correctly simulate a yacht’s behavior in actual sailing conditions. The simulation results from the FSI model compare very well with the experimental data for steady sailing conditions. For the unsteady conditions obtained in head waves, the first results show a good agreement between measurements and simulation.