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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 25 Jul 2024 03:23:23 GMT2024-07-25T03:23:23ZAn 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.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.Computational 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; ASTOLFI, Jacques Andre; DENISET, François; 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, AntoineASTOLFI, Jacques AndreDENISET, FrançoisSIGRIST, 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.