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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 21 May 2024 08:07:19 GMT2024-05-21T08:07:19ZAnalysis of added mass in cavitating flow
http://hdl.handle.net/10985/8836
Analysis of added mass in cavitating flow
BENAOUICHA, Mustapha; ASTOLFI, Jacques Andre
The paper addresses a theoretical study of the added mass effect in cavitating flow.The cavitation is considered to induce a strong time–space variation of the fluid density at the interface between an inviscid fluid and a three-degree-of-freedom rigid section. The coupled problem is then simplified to a Laplace equation written for the pressure with a boundary condition at the fluid–structure interface depending on the acceleration, the velocity of the structure and on the rate of change of flow density. It is shown that contrary to the homogeneous flow, the added mass operator is not symmetrical and depends on the flow through fluid density variation. The added mass coefficients decrease as the cavitation increases which should induce an increase of the natural structural frequencies. The model shows also an added damping operator related to the rate of change of flow density. Added damping coefficients are found to be positive or negative according to the rate of change of the fluid density, indicating the possibility of instability development between flexible structures and unsteady cavitating flows.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/88362012-01-01T00:00:00ZBENAOUICHA, MustaphaASTOLFI, Jacques AndreThe paper addresses a theoretical study of the added mass effect in cavitating flow.The cavitation is considered to induce a strong time–space variation of the fluid density at the interface between an inviscid fluid and a three-degree-of-freedom rigid section. The coupled problem is then simplified to a Laplace equation written for the pressure with a boundary condition at the fluid–structure interface depending on the acceleration, the velocity of the structure and on the rate of change of flow density. It is shown that contrary to the homogeneous flow, the added mass operator is not symmetrical and depends on the flow through fluid density variation. The added mass coefficients decrease as the cavitation increases which should induce an increase of the natural structural frequencies. The model shows also an added damping operator related to the rate of change of flow density. Added damping coefficients are found to be positive or negative according to the rate of change of the fluid density, indicating the possibility of instability development between flexible structures and unsteady cavitating flows.An experimental analysis of fluid structure interaction on a flexible hydrofoil in various flow regimes including cavitating flow
http://hdl.handle.net/10985/8998
An experimental analysis of fluid structure interaction on a flexible hydrofoil in various flow regimes including cavitating flow
DUCOIN, Antoine; ASTOLFI, Jacques Andre; SIGRIST, Jean-François
The structural response of a rectangular cantilevered flexible hydrofoil submitted to various flow regimes is analyzed through an original experiment carried out in a hydrodynamic tunnel at a Reynolds number of 0.75 × 10 6 . The experiment considers static and transient regimes. The latter consists of transient pitching motions at low and fast pitching velocities. The experiments are also performed for cavitating flow. The structural response is analyzed through the measurement of the free foil tip section displacement using a high speed video camera and surface velocity vibrations using a laser doppler vibrometer. In non cavitating flows, it is shown that the structural response is linked to the hydrodynamic loading, which is governed by viscous effects such as laminar to turbulent transition induced by Laminar Separation Bubble (LSB), and stall. It is also observed that the foil elastic displacement depends strongly on the pitching velocity. Large overshoots and hysteresis effect are observed as the pitching velocity increases. Cavitation induces a large increase of the vibration level due to hydrodynamic loading unsteadiness and change of modal response for specific frequencies. The experimental results presented in this paper will help to develop high fidelity fluid–structure interaction models in naval applications.
The authors gratefully acknowledge the technical staff of IRENav for its contribution to the experimental set up.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/89982012-01-01T00:00:00ZDUCOIN, AntoineASTOLFI, Jacques AndreSIGRIST, Jean-FrançoisThe structural response of a rectangular cantilevered flexible hydrofoil submitted to various flow regimes is analyzed through an original experiment carried out in a hydrodynamic tunnel at a Reynolds number of 0.75 × 10 6 . The experiment considers static and transient regimes. The latter consists of transient pitching motions at low and fast pitching velocities. The experiments are also performed for cavitating flow. The structural response is analyzed through the measurement of the free foil tip section displacement using a high speed video camera and surface velocity vibrations using a laser doppler vibrometer. In non cavitating flows, it is shown that the structural response is linked to the hydrodynamic loading, which is governed by viscous effects such as laminar to turbulent transition induced by Laminar Separation Bubble (LSB), and stall. It is also observed that the foil elastic displacement depends strongly on the pitching velocity. Large overshoots and hysteresis effect are observed as the pitching velocity increases. Cavitation induces a large increase of the vibration level due to hydrodynamic loading unsteadiness and change of modal response for specific frequencies. The experimental results presented in this paper will help to develop high fidelity fluid–structure interaction models in naval applications.Cavity induced vibration of flexible hydrofoils
http://hdl.handle.net/10985/8992
Cavity induced vibration of flexible hydrofoils
AKCABAY, Deniz Tolga; CHAE, Eun Jung; YOUNG, Yin Lu; DUCOIN, Antoine; ASTOLFI, Jacques Andre
The objective of this work is to investigate the influence of cavity-induced vibrations on the dynamic response and stability of a NACA66 hydrofoil at 8° angle of attack at Re=750 000 via combined experimental measurements and numerical simulations. The rectangular, cantilevered hydrofoil is assumed to be rigid in the chordwise direction, while the spanwise bending and twisting deformations are represented using a two-degrees-of-freedom structural model. The multiphase flow is modeled with an incompressible, unsteady Reynolds Averaged Navier–Stokes solver with the k–ω Shear Stress Transport (SST) turbulence closure model, while the phase evolutions are modeled with a mass-transport equation based cavitation model. The numerical predictions are compared with experimental measurements across a range of cavitation numbers for a rigid and a flexible hydrofoil with the same undeformed geometries. The results showed that foil flexibility can lead to: (1) focusing – locking – of the frequency content of the vibrations to the nearest sub-harmonics of the foil׳s wetted natural frequencies, and (2) broadening of the frequency content of the vibrations in the unstable cavitation regime, where amplifications are observed in the sub-harmonics of the foil natural frequencies. Cavitation was also observed to cause frequency modulation, as the fluid density, and hence fluid induced (inertial, damping, and disturbing) forces fluctuated with unsteady cavitation.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/89922014-01-01T00:00:00ZAKCABAY, Deniz TolgaCHAE, Eun JungYOUNG, Yin LuDUCOIN, AntoineASTOLFI, Jacques AndreThe objective of this work is to investigate the influence of cavity-induced vibrations on the dynamic response and stability of a NACA66 hydrofoil at 8° angle of attack at Re=750 000 via combined experimental measurements and numerical simulations. The rectangular, cantilevered hydrofoil is assumed to be rigid in the chordwise direction, while the spanwise bending and twisting deformations are represented using a two-degrees-of-freedom structural model. The multiphase flow is modeled with an incompressible, unsteady Reynolds Averaged Navier–Stokes solver with the k–ω Shear Stress Transport (SST) turbulence closure model, while the phase evolutions are modeled with a mass-transport equation based cavitation model. The numerical predictions are compared with experimental measurements across a range of cavitation numbers for a rigid and a flexible hydrofoil with the same undeformed geometries. The results showed that foil flexibility can lead to: (1) focusing – locking – of the frequency content of the vibrations to the nearest sub-harmonics of the foil׳s wetted natural frequencies, and (2) broadening of the frequency content of the vibrations in the unstable cavitation regime, where amplifications are observed in the sub-harmonics of the foil natural frequencies. Cavitation was also observed to cause frequency modulation, as the fluid density, and hence fluid induced (inertial, damping, and disturbing) forces fluctuated with unsteady cavitation.Effect of the laminar separation bubble induced transition on the hydrodynamic performance of a hydrofoil
http://hdl.handle.net/10985/8996
Effect of the laminar separation bubble induced transition on the hydrodynamic performance of a hydrofoil
DELAFIN, Pierre-Luc; DENISET, François; ASTOLFI, Jacques Andre
The present study deals with the effect of the laminar separation bubble (LSB) induced transition on the lift, drag and moment coefficients of a hydrofoil. A 2D numerical study, based on the SST γ –Reθ transition model of ANSYS-CFX⃝R , is conducted on a NACA66 hydrofoil. Angles of attack range from −4° to 14° and the chord-based Reynolds number is Re = 7.5 × 105. An experimental investigation is carried out in the French naval academy research institute’s hydrodynamic tunnel based on the measurements of lift, drag and moment. Experiments on a smooth, mirror finished, hydrofoil enable comparison with RANS calculations using the transition model. Experiments with a roughness added on the leading edge enable comparison with RANS calculations using the SST fully turbulent model. For angles of attack below 6°, the LSB triggered laminar to turbulent transition of the boundary layers of the suction and pressure sides is located near the trailing edge of the smooth NACA66. As the angle of attack reaches 6°, the LSB suddenly moves to the leading edge on the suction side while transition is located at the trailing edge on the pressure side. The smooth hydrofoil shows higher CL and CM and lower CD than the rough leading edge one from −4° to 6°. Both experiments lead to the same coefficients from 6° to 14°. The calculations show that both models are in good agreement with their corresponding experiments. Velocity profiles in the vicinity of the LSB at an angle of attack of 2° and pressure coefficients of the calculations using the transition model are compared with published experimental studies and show very good agreement. The SST γ –Reθ transition model proves to be a relevant, even essential, prediction tool for lifting bodies operating at a moderate Reynolds number.
The authors thank the technical staff of IRENav for their contribution to the experimental set up.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/89962014-01-01T00:00:00ZDELAFIN, Pierre-LucDENISET, FrançoisASTOLFI, Jacques AndreThe present study deals with the effect of the laminar separation bubble (LSB) induced transition on the lift, drag and moment coefficients of a hydrofoil. A 2D numerical study, based on the SST γ –Reθ transition model of ANSYS-CFX⃝R , is conducted on a NACA66 hydrofoil. Angles of attack range from −4° to 14° and the chord-based Reynolds number is Re = 7.5 × 105. An experimental investigation is carried out in the French naval academy research institute’s hydrodynamic tunnel based on the measurements of lift, drag and moment. Experiments on a smooth, mirror finished, hydrofoil enable comparison with RANS calculations using the transition model. Experiments with a roughness added on the leading edge enable comparison with RANS calculations using the SST fully turbulent model. For angles of attack below 6°, the LSB triggered laminar to turbulent transition of the boundary layers of the suction and pressure sides is located near the trailing edge of the smooth NACA66. As the angle of attack reaches 6°, the LSB suddenly moves to the leading edge on the suction side while transition is located at the trailing edge on the pressure side. The smooth hydrofoil shows higher CL and CM and lower CD than the rough leading edge one from −4° to 6°. Both experiments lead to the same coefficients from 6° to 14°. The calculations show that both models are in good agreement with their corresponding experiments. Velocity profiles in the vicinity of the LSB at an angle of attack of 2° and pressure coefficients of the calculations using the transition model are compared with published experimental studies and show very good agreement. The SST γ –Reθ transition model proves to be a relevant, even essential, prediction tool for lifting bodies operating at a moderate Reynolds number.An experimental study of boundary-layer transition induced vibrations on a hydrofoil
http://hdl.handle.net/10985/8905
An experimental study of boundary-layer transition induced vibrations on a hydrofoil
DUCOIN, Antoine; ASTOLFI, Jacques Andre; GOBERT, Marie-Laure
This paper aims at characterizing experimentally laminar to turbulent transition induced vibrations. Here, the transition is known to be triggered by a Laminar Separation Bubble that results from a laminar separation of the boundary-layer flow on a hydrofoil. In this study we consider two NACA66312 (Mod) laminar hydrofoils at low angles of incidence (mostly 2° and 4°) and Reynolds numbers ranging from Re=450 000 to 1 200 000, in order to get transitional regimes. The first hydrofoil, made of steel (E=2.1×1011 Pa), is referred to as the rigid hydrofoil, although it is seen to vibrate under the action of the LSB. To better understand the possible interaction between the flow and the foil vibrations, vibration measurements are repeated using a flexible hydrofoil (E=3×109 Pa) of same geometry (under zero loading) and in close configurations. The experiments are carried out at the French Naval Academy Research Institute (IRENav, France). Wall pressure and flow velocity measurements enable a characterization of the laminar separation bubble and the identification of a vortex shedding at a given frequency. It is hence shown that the boundary-layer transition induces important foil vibrations, whose characteristics in terms of frequency and amplitude depend on the vortex shedding frequency, and can be coupled with natural frequencies of the hydrofoils.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/89052012-01-01T00:00:00ZDUCOIN, AntoineASTOLFI, Jacques AndreGOBERT, Marie-LaureThis paper aims at characterizing experimentally laminar to turbulent transition induced vibrations. Here, the transition is known to be triggered by a Laminar Separation Bubble that results from a laminar separation of the boundary-layer flow on a hydrofoil. In this study we consider two NACA66312 (Mod) laminar hydrofoils at low angles of incidence (mostly 2° and 4°) and Reynolds numbers ranging from Re=450 000 to 1 200 000, in order to get transitional regimes. The first hydrofoil, made of steel (E=2.1×1011 Pa), is referred to as the rigid hydrofoil, although it is seen to vibrate under the action of the LSB. To better understand the possible interaction between the flow and the foil vibrations, vibration measurements are repeated using a flexible hydrofoil (E=3×109 Pa) of same geometry (under zero loading) and in close configurations. The experiments are carried out at the French Naval Academy Research Institute (IRENav, France). Wall pressure and flow velocity measurements enable a characterization of the laminar separation bubble and the identification of a vortex shedding at a given frequency. It is hence shown that the boundary-layer transition induces important foil vibrations, whose characteristics in terms of frequency and amplitude depend on the vortex shedding frequency, and can be coupled with natural frequencies of the hydrofoils.Concepts, Modélisation et Commandes des Hydroliennes
http://hdl.handle.net/10985/8832
Concepts, Modélisation et Commandes des Hydroliennes
BENBOUZID, Mohamed; ASTOLFI, Jacques Andre; BACHA, Seddik; CHARPENTIER, Jean-Frederic; MACHMOUN, Mohamed; MAITRE, Thierry; ROYE, Daniel
Face au problème de la gestion des déchets nucléaire et aux émissions de gaz à effet de serre, les énergies renouvelables occupent une place avancée parmi les énergies d’avenir grâce à leur faible impact sur l’environnement ; d’autant plus que ces énergies jouent un rôle important dans la lutte contre le changement climatique et dans le développement économique de certains pays. Ces atouts, alliés à des technologies de plus en plus performantes, favorisent le développement des énergies renouvelables mais de manière encore très inégale selon le type de ressources considérées. Une de ces énergies renouvelables, l’énergie hydrolienne, suscite depuis quelques années un intérêt particulier du fait de ses nombreux avantages. En effet, la force et la vitesse des courants de marée, phénomène prédictible, peuvent être connues des décennies à l’avance. Pour une hydrolienne placée à un endroit donné, il est donc possible, par opposition aux autres énergies renouvelables, dépendant des conditions météorologiques, de connaître à tout moment quelle sera, au premier ordre, la puissance extractible par les gestionnaires de réseaux d’énergie afin d’alimenter ses consommateurs. De plus, les pays d’Europe de l’Ouest et en particulier le Royaume Uni et la France possèdent de nombreux sites près des cotes ou cette énergie est exploitable dans de bonnes conditions économiques. Le but de chapitre est la présentation succincte des principaux concepts hydroliens puis de donner des éléments quant à la modélisation d’un concept de base, et enfin introduire des éléments de contrôle/commande
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/88322011-01-01T00:00:00ZBENBOUZID, MohamedASTOLFI, Jacques AndreBACHA, SeddikCHARPENTIER, Jean-FredericMACHMOUN, MohamedMAITRE, ThierryROYE, DanielFace au problème de la gestion des déchets nucléaire et aux émissions de gaz à effet de serre, les énergies renouvelables occupent une place avancée parmi les énergies d’avenir grâce à leur faible impact sur l’environnement ; d’autant plus que ces énergies jouent un rôle important dans la lutte contre le changement climatique et dans le développement économique de certains pays. Ces atouts, alliés à des technologies de plus en plus performantes, favorisent le développement des énergies renouvelables mais de manière encore très inégale selon le type de ressources considérées. Une de ces énergies renouvelables, l’énergie hydrolienne, suscite depuis quelques années un intérêt particulier du fait de ses nombreux avantages. En effet, la force et la vitesse des courants de marée, phénomène prédictible, peuvent être connues des décennies à l’avance. Pour une hydrolienne placée à un endroit donné, il est donc possible, par opposition aux autres énergies renouvelables, dépendant des conditions météorologiques, de connaître à tout moment quelle sera, au premier ordre, la puissance extractible par les gestionnaires de réseaux d’énergie afin d’alimenter ses consommateurs. De plus, les pays d’Europe de l’Ouest et en particulier le Royaume Uni et la France possèdent de nombreux sites près des cotes ou cette énergie est exploitable dans de bonnes conditions économiques. Le but de chapitre est la présentation succincte des principaux concepts hydroliens puis de donner des éléments quant à la modélisation d’un concept de base, et enfin introduire des éléments de contrôle/commandeComputational and experimental investigation of flow over a transient pitching hydrofoil
http://hdl.handle.net/10985/10205
Computational and experimental investigation of flow over a transient pitching hydrofoil
DUCOIN, Antoine; DENISET, François; ASTOLFI, Jacques Andre; SIGRIST, Jean-François
The present study is developed within the framework of marine structure design operating in transient regimes. It deals with an experimental and numerical investigation of the time–space distribution of the wall-pressure field on a NACA66 hydrofoil undergoing a transient up-and-down pitching motion from 0 to 15 at four pitching velocities and a Reynolds number Re¼ 0.75 106. The experimental investigation is performed using an array of wall-pressure transducers located on the suction side and by means of time–frequency analysis and Empirical Modal Decomposition method. The numerical study is conducted for the same flow conditions. It is based on a 2D RANS code including mesh reconstruction and an ALE formulation in order to take into account the foil rotation and the tunnel walls. Due to the moderate Reynolds number, a laminar to turbulent transition model was also activated. For the operating flow conditions of the study, experimental and numerical flow analysis revealed that the flow experiences complex boundary layer events as leading-edge laminar separation bubble, laminar to turbulent transition, trailing-edge separation and flow detachment at stall. Although the flow is relatively complex, the calculated wall pressure shows a quite good agreement with the experiment provided that the mesh resolution and the temporal discretization are carefully selected depending on the pitching velocity. It is particularly shown that the general trend of the wall pressure (low frequency) is rather well predicted for the four pitching velocities with for instance a net inflection of the wall pressure when transition occurs. The inflection zone is reduced as the pitching velocity increases and tends to disappear for the highest pitching velocity. Conversely, high frequency wall-pressure fluctuations observed experimentally are not captured by the RANS model. Based on the good agreement with experiment, the model is then used to investigate the effects of the pitching velocity on boundary layer events and on hydrodynamic loadings. It is shown that increasing the pitching velocity tends to delay the laminar-to-turbulence transition and even to suppress it for the highest pitching velocity during the pitch-up motion. It induces also an increase of the stall angle (compared to quasi-static one) and an increase of the hysteresis effect during pitch-down motion resulting to a significant increase of the hydrodynamic loading.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10985/102052009-01-01T00:00:00ZDUCOIN, AntoineDENISET, FrançoisASTOLFI, Jacques AndreSIGRIST, Jean-FrançoisThe present study is developed within the framework of marine structure design operating in transient regimes. It deals with an experimental and numerical investigation of the time–space distribution of the wall-pressure field on a NACA66 hydrofoil undergoing a transient up-and-down pitching motion from 0 to 15 at four pitching velocities and a Reynolds number Re¼ 0.75 106. The experimental investigation is performed using an array of wall-pressure transducers located on the suction side and by means of time–frequency analysis and Empirical Modal Decomposition method. The numerical study is conducted for the same flow conditions. It is based on a 2D RANS code including mesh reconstruction and an ALE formulation in order to take into account the foil rotation and the tunnel walls. Due to the moderate Reynolds number, a laminar to turbulent transition model was also activated. For the operating flow conditions of the study, experimental and numerical flow analysis revealed that the flow experiences complex boundary layer events as leading-edge laminar separation bubble, laminar to turbulent transition, trailing-edge separation and flow detachment at stall. Although the flow is relatively complex, the calculated wall pressure shows a quite good agreement with the experiment provided that the mesh resolution and the temporal discretization are carefully selected depending on the pitching velocity. It is particularly shown that the general trend of the wall pressure (low frequency) is rather well predicted for the four pitching velocities with for instance a net inflection of the wall pressure when transition occurs. The inflection zone is reduced as the pitching velocity increases and tends to disappear for the highest pitching velocity. Conversely, high frequency wall-pressure fluctuations observed experimentally are not captured by the RANS model. Based on the good agreement with experiment, the model is then used to investigate the effects of the pitching velocity on boundary layer events and on hydrodynamic loadings. It is shown that increasing the pitching velocity tends to delay the laminar-to-turbulence transition and even to suppress it for the highest pitching velocity during the pitch-up motion. It induces also an increase of the stall angle (compared to quasi-static one) and an increase of the hysteresis effect during pitch-down motion resulting to a significant increase of the hydrodynamic loading.Experimental analysis of trailing edge hydroelastic coupling on a hydrofoil
http://hdl.handle.net/10985/24787
Experimental analysis of trailing edge hydroelastic coupling on a hydrofoil
FRANCOIS, Paul; ASTOLFI, Jacques Andre; AMANDOLESE, Xavier
This paper explores the conditions for hydroelastic trailing edge vibrations generating tonal noise on a NACA0015 aluminium hydrofoil clamped in a hydrodynamic tunnel. Tests were performed for Reynolds numbers, ranging from 200 000 up to 1 200 000 and various angles of attack, from 0 up to 10°. A laser vibrometer was used to characterize the hydrofoil vibratory response. Time Resolved Particle Image Velocimetry (TR-PIV) was used to scrutinize the origin of the hydrodynamic excitation mechanism. Hydroelastic trailing edge vibrations of significant amplitude were observed at moderate angles of attack 4 ≤ α ≤ 8.5°, for Reynolds number such that the pressure side boundary layer transition was located close to the trailing edge, with a frequency signature allowing a lock-in with the hydrofoil trailing edge structural mode. Two passive solutions were tested to mitigate this hydroelastic flow-induced vibration: a truncated hydrofoil and a triggered one. The truncated configuration slightly impacts the vibration while triggering the pressure side boundary layer transition ahead of the trailing edge eliminates the trailing edge vibrations with negligible impact on the hydrofoil hydrodynamics performances.
Tue, 23 Jan 2024 00:00:00 GMThttp://hdl.handle.net/10985/247872024-01-23T00:00:00ZFRANCOIS, PaulASTOLFI, Jacques AndreAMANDOLESE, XavierThis paper explores the conditions for hydroelastic trailing edge vibrations generating tonal noise on a NACA0015 aluminium hydrofoil clamped in a hydrodynamic tunnel. Tests were performed for Reynolds numbers, ranging from 200 000 up to 1 200 000 and various angles of attack, from 0 up to 10°. A laser vibrometer was used to characterize the hydrofoil vibratory response. Time Resolved Particle Image Velocimetry (TR-PIV) was used to scrutinize the origin of the hydrodynamic excitation mechanism. Hydroelastic trailing edge vibrations of significant amplitude were observed at moderate angles of attack 4 ≤ α ≤ 8.5°, for Reynolds number such that the pressure side boundary layer transition was located close to the trailing edge, with a frequency signature allowing a lock-in with the hydrofoil trailing edge structural mode. Two passive solutions were tested to mitigate this hydroelastic flow-induced vibration: a truncated hydrofoil and a triggered one. The truncated configuration slightly impacts the vibration while triggering the pressure side boundary layer transition ahead of the trailing edge eliminates the trailing edge vibrations with negligible impact on the hydrofoil hydrodynamics performances.Nonlinear disturbance evolution in a two-dimensional boundary layer along an elastic plate and induced radiated sound
http://hdl.handle.net/10985/8934
Nonlinear disturbance evolution in a two-dimensional boundary layer along an elastic plate and induced radiated sound
GOBERT, Marie-Laure; EHRENSTEIN, Uwe; ASTOLFI, Jacques Andre; BOT, Patrick
The interaction between a boundary-layer flow and an elastic plate is addressed by direct numerical simulation, taking into account the full coupling between the fluid flow and the flexible wall. The convectively unstable flow state is harmonically forced and two-dimensional nonlinearly saturated wavelike disturbances are computed along archetype-plates with respect to stiffness and natural frequencies. In the aim of determining the low-Mach-number radiated sound for the system, the simulation data are used to solve the Lighthill’s equation in terms of a Green’s function in the wavenumber-frequency space. Different degrees of fluid-structure coupling are implemented in the radiated sound model and the resulting acoustic pressure levels are compared. The sound radiation levels are shown to be increased in the presence of flexible walls with however significant differences in the radiated pressure levels for different coupling assumptions
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/89342010-01-01T00:00:00ZGOBERT, Marie-LaureEHRENSTEIN, UweASTOLFI, Jacques AndreBOT, PatrickThe interaction between a boundary-layer flow and an elastic plate is addressed by direct numerical simulation, taking into account the full coupling between the fluid flow and the flexible wall. The convectively unstable flow state is harmonically forced and two-dimensional nonlinearly saturated wavelike disturbances are computed along archetype-plates with respect to stiffness and natural frequencies. In the aim of determining the low-Mach-number radiated sound for the system, the simulation data are used to solve the Lighthill’s equation in terms of a Green’s function in the wavenumber-frequency space. Different degrees of fluid-structure coupling are implemented in the radiated sound model and the resulting acoustic pressure levels are compared. The sound radiation levels are shown to be increased in the presence of flexible walls with however significant differences in the radiated pressure levels for different coupling assumptionsDiscontinuity 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.