The effect of spanwise clearance on the critical velocity for fluttering of a cantilevered plate ... more The effect of spanwise clearance on the critical velocity for fluttering of a cantilevered plate in a channel flow is addressed experimentally. It is found that the critical velocity is influenced by the presence of the walls when the ratio between the clearance and the length of the plate C/L is less than 0.1 and slowly converges to the critical velocity predicted by models considering infinite span plates. These results are in good agreement with the predictions of a potential flow model taking into account spanwise confinement.
We present a weakly non-linear model of a piezoelctric flag immersed in an axial flow. Numerical ... more We present a weakly non-linear model of a piezoelctric flag immersed in an axial flow. Numerical simulations based on Galerkin projections are carried out in order to evaluate the coupling between the flapping piezo-electric flag and a purely resistive circuit intended to simulate the electric energy harvesting circuit. The numerical simulations allow to point out the relevant physical parameters governing the apparition of the flapping instability, power conversion and system's harvesting efficiency.
We investigate the relationship between the local and global bending motion of fluid conveying pi... more We investigate the relationship between the local and global bending motion of fluid conveying pipes on an elastic foundation. The local approach refers to an infinite pipe without taking into account its finite ends while in the global approach we consider a pipe of finite length with a given set of boundary conditions. Several kinds of propagating disturbances are identified
We investigate the instability properties of one-dimensional systems of finite length that can be... more We investigate the instability properties of one-dimensional systems of finite length that can be described by a local wave equation and a set of boundary,conditions. A method,to quantify the respective contributions of the local instability and of wave reflections in the global instability is proposed. This allows to differentiate instabilities that emanate,from wave propagation from instabilities due to wave
Fluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's me... more Fluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's mechanical deformation into electric energy in an output circuit. This work focuses on the influence of the arrangement of the piezoelectric electrodes along the plate's surface on the energy harvesting efficiency of the system, using a combination of experiments and numerical simulations. A weakly non-linear model of a plate in axial flow, equipped with a discrete number of piezoelectric patches is derived and confronted to experimental results. Numerical simulations are then used to optimize the position and dimensions of the piezoelectric electrodes. These optimal configurations can be understood physically in the limit of small and large electromechanical coupling. * [email protected] † [email protected] ‡ [email protected] arXiv:1501.04303v1 [physics.flu-dyn]
ABSTRACT This work aims to improve understanding of the damping induced by an axial flow on a rig... more ABSTRACT This work aims to improve understanding of the damping induced by an axial flow on a rigid cylinder undergoing small lateral oscillations within the framework of the quasistatic assumption. The study focuses on the normal force exerted on the cylinder for a Reynolds number of Re = 24 000 (based on the cylinder diameter and axial flow velocity). Both dynamic and static approaches are investigated. With the static approach, fluid forces, pressure distributions and velocity fields are measured for different yaw angles and cylinder lengths in a wind tunnel. It is found that for yaw angles smaller than 5 degrees, the normal force varies linearly with the angle and is fully dominated by its lift component. The lift originates from the high pressure coefficient at the front of the cylinder, which is found to depend linearly on the angle, and from a base pressure coefficient that remains close to zero independent of the yaw angle. At the base, a flow deficit and two counter-rotating vortices are observed. A numerical simulation using a k-omega shear stress transport turbulence model confirms the static experimental results. A dynamic experiment conducted in a water tunnel brings out damping-rate values during free oscillations of the cylinder. As expected from the linear dependence of the normal force on the yaw angle observed with the static approach, the damping rate increases linearly with the axial flow velocity. Satisfactory agreement is found between the two approaches.
The paper provides experimental data on flow separation from a model of the human vocal folds. Da... more The paper provides experimental data on flow separation from a model of the human vocal folds. Data were measured on a four-times scaled physical model, where one vocal fold was fixed and the other oscillated due to fluidstructure interaction. The vocal folds were fabricated from silicone rubber and placed on elastic support in the wall of a transparent wind tunnel. A PIV system was used to visualize the flow fields immediately downstream of the glottis and to measure the velocity fields. From the visualizations, the position of the flow separation point was evaluated using a semiautomatic procedure and plotted for different airflow velocities. The separation point position was quantified relative to the orifice width separately for the left and right vocal folds to account for flow asymmetry. The results indicate that the flow separation point remains close to the narrowest cross-section during most of the vocal fold vibration cycle, but moves significantly further downstream shortly prior to and after glottal closure.
Abstract. Shape Memory Alloys (SMAs) present unusual behaviour compared to more standard linear e... more Abstract. Shape Memory Alloys (SMAs) present unusual behaviour compared to more standard linear elastic materials. Indeed, they can accomodate large re-versibe strain (pseudo-elasticity) or recover their shape, after being strained, by simple heating (shape ...
Page 1. Accepted Manuscript Not Copyedited 1 Practical Assessment of Real-Time Impact Point Estim... more Page 1. Accepted Manuscript Not Copyedited 1 Practical Assessment of Real-Time Impact Point Estimators for Smart Weapons Frank Fresconi1 and Gene Cooper2 US Army Research Laboratory, Aberdeen Proving Ground, MD, 21005 and Mark Costello3 ...
ABSTRACT This study investigates the flow around a cylinder in a near-axial flow at a Reynolds nu... more ABSTRACT This study investigates the flow around a cylinder in a near-axial flow at a Reynolds number of 27,000. Both computational fluid dynamics (CFD) calculations and experiments are performed. Time-mean values of lift force coefficient are investigated against the inclination of the cylinder in the domain of low inclinations (<15 deg). A pressure distribution and flow profiles are also measured and extracted from the CFD calculation results for a characteristic inclination alpha = 5 deg. Numerical results for force and pressure show fair agreement with experiments for inclination below 5 deg and reveal that at low angles, the lift force is proportional to the angle. In the framework of a quasi-static approach, the instantaneous damping force exerted on a cylinder oscillating in axial flow is equivalent to the normal force exerted on a cylinder placed in an oblique flow.
The effect of spanwise clearance on the critical velocity for fluttering of a cantilevered plate ... more The effect of spanwise clearance on the critical velocity for fluttering of a cantilevered plate in a channel flow is addressed experimentally. It is found that the critical velocity is influenced by the presence of the walls when the ratio between the clearance and the length of the plate C/L is less than 0.1 and slowly converges to the critical velocity predicted by models considering infinite span plates. These results are in good agreement with the predictions of a potential flow model taking into account spanwise confinement.
We present a weakly non-linear model of a piezoelctric flag immersed in an axial flow. Numerical ... more We present a weakly non-linear model of a piezoelctric flag immersed in an axial flow. Numerical simulations based on Galerkin projections are carried out in order to evaluate the coupling between the flapping piezo-electric flag and a purely resistive circuit intended to simulate the electric energy harvesting circuit. The numerical simulations allow to point out the relevant physical parameters governing the apparition of the flapping instability, power conversion and system's harvesting efficiency.
We investigate the relationship between the local and global bending motion of fluid conveying pi... more We investigate the relationship between the local and global bending motion of fluid conveying pipes on an elastic foundation. The local approach refers to an infinite pipe without taking into account its finite ends while in the global approach we consider a pipe of finite length with a given set of boundary conditions. Several kinds of propagating disturbances are identified
We investigate the instability properties of one-dimensional systems of finite length that can be... more We investigate the instability properties of one-dimensional systems of finite length that can be described by a local wave equation and a set of boundary,conditions. A method,to quantify the respective contributions of the local instability and of wave reflections in the global instability is proposed. This allows to differentiate instabilities that emanate,from wave propagation from instabilities due to wave
Fluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's me... more Fluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's mechanical deformation into electric energy in an output circuit. This work focuses on the influence of the arrangement of the piezoelectric electrodes along the plate's surface on the energy harvesting efficiency of the system, using a combination of experiments and numerical simulations. A weakly non-linear model of a plate in axial flow, equipped with a discrete number of piezoelectric patches is derived and confronted to experimental results. Numerical simulations are then used to optimize the position and dimensions of the piezoelectric electrodes. These optimal configurations can be understood physically in the limit of small and large electromechanical coupling. * [email protected] † [email protected] ‡ [email protected] arXiv:1501.04303v1 [physics.flu-dyn]
ABSTRACT This work aims to improve understanding of the damping induced by an axial flow on a rig... more ABSTRACT This work aims to improve understanding of the damping induced by an axial flow on a rigid cylinder undergoing small lateral oscillations within the framework of the quasistatic assumption. The study focuses on the normal force exerted on the cylinder for a Reynolds number of Re = 24 000 (based on the cylinder diameter and axial flow velocity). Both dynamic and static approaches are investigated. With the static approach, fluid forces, pressure distributions and velocity fields are measured for different yaw angles and cylinder lengths in a wind tunnel. It is found that for yaw angles smaller than 5 degrees, the normal force varies linearly with the angle and is fully dominated by its lift component. The lift originates from the high pressure coefficient at the front of the cylinder, which is found to depend linearly on the angle, and from a base pressure coefficient that remains close to zero independent of the yaw angle. At the base, a flow deficit and two counter-rotating vortices are observed. A numerical simulation using a k-omega shear stress transport turbulence model confirms the static experimental results. A dynamic experiment conducted in a water tunnel brings out damping-rate values during free oscillations of the cylinder. As expected from the linear dependence of the normal force on the yaw angle observed with the static approach, the damping rate increases linearly with the axial flow velocity. Satisfactory agreement is found between the two approaches.
The paper provides experimental data on flow separation from a model of the human vocal folds. Da... more The paper provides experimental data on flow separation from a model of the human vocal folds. Data were measured on a four-times scaled physical model, where one vocal fold was fixed and the other oscillated due to fluidstructure interaction. The vocal folds were fabricated from silicone rubber and placed on elastic support in the wall of a transparent wind tunnel. A PIV system was used to visualize the flow fields immediately downstream of the glottis and to measure the velocity fields. From the visualizations, the position of the flow separation point was evaluated using a semiautomatic procedure and plotted for different airflow velocities. The separation point position was quantified relative to the orifice width separately for the left and right vocal folds to account for flow asymmetry. The results indicate that the flow separation point remains close to the narrowest cross-section during most of the vocal fold vibration cycle, but moves significantly further downstream shortly prior to and after glottal closure.
Abstract. Shape Memory Alloys (SMAs) present unusual behaviour compared to more standard linear e... more Abstract. Shape Memory Alloys (SMAs) present unusual behaviour compared to more standard linear elastic materials. Indeed, they can accomodate large re-versibe strain (pseudo-elasticity) or recover their shape, after being strained, by simple heating (shape ...
Page 1. Accepted Manuscript Not Copyedited 1 Practical Assessment of Real-Time Impact Point Estim... more Page 1. Accepted Manuscript Not Copyedited 1 Practical Assessment of Real-Time Impact Point Estimators for Smart Weapons Frank Fresconi1 and Gene Cooper2 US Army Research Laboratory, Aberdeen Proving Ground, MD, 21005 and Mark Costello3 ...
ABSTRACT This study investigates the flow around a cylinder in a near-axial flow at a Reynolds nu... more ABSTRACT This study investigates the flow around a cylinder in a near-axial flow at a Reynolds number of 27,000. Both computational fluid dynamics (CFD) calculations and experiments are performed. Time-mean values of lift force coefficient are investigated against the inclination of the cylinder in the domain of low inclinations (<15 deg). A pressure distribution and flow profiles are also measured and extracted from the CFD calculation results for a characteristic inclination alpha = 5 deg. Numerical results for force and pressure show fair agreement with experiments for inclination below 5 deg and reveal that at low angles, the lift force is proportional to the angle. In the framework of a quasi-static approach, the instantaneous damping force exerted on a cylinder oscillating in axial flow is equivalent to the normal force exerted on a cylinder placed in an oblique flow.
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