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Damping identification of lightly damped linear dynamic systems using Common-base Proper Orthogonal Decomposition Andrianne, Thomas ; Dimitriadis, Grigorios in Mechanical Systems & Signal Processing (2012), 28 This paper presents a new technique to identify the damping of linear systems. It is developed from the Proper Orthogonal Decomposition (POD) of the free response of the system and extended to the ... [more ▼] This paper presents a new technique to identify the damping of linear systems. It is developed from the Proper Orthogonal Decomposition (POD) of the free response of the system and extended to the recently proposed Common-base POD (CPOD). The present application of CPOD considers simultaneously several free responses of the system to different initial conditions. The eigen-decomposition of the co-variance matrix leads to a unique vector basis which is likely to contain more information about the dynamics of the system than a vector basis obtained by the classic POD technique. The ability of the technique to estimate the mode shapes and the modal damping is demonstrated on a simulated mass-spring-damper system. Two different distributions of masses are considered in order to confront the CPOD analysis to the intrinsic limitation of POD, i.e. that the mode shapes are identified exactly only if the mass matrix is proportional to the identity matrix. It is shown that the identification of the damping is still possible when the modes are not orthonormal. The robustness of the technique is demonstrated in the presence of noise in the responses of the system and through an experimental application with comparison with other identifications techniques. [less ▲] Detailed reference viewed: 86 (15 ULg)Unsteady Navier-Stokes simulation of low-Reynolds stall flutter Yabili, Sacha ; ; Dimitriadis, Grigorios in Proceedings of the 50th AIAA Aerospace Sciences Meeting (2012, January) A solver has been developed within the OpenFoam framework to compute large amplitude motion of two-dimensional rigid configurations. The results obtained with this code were successfully validated on ... [more ▼] A solver has been developed within the OpenFoam framework to compute large amplitude motion of two-dimensional rigid configurations. The results obtained with this code were successfully validated on rigid airfoils at static and dynamic conditions, as well as correlated with experimental data and numerical solutions from similar unsteady solvers. The results demonstrate that current computational methods are, within the constraints imposed by spatial grids, temporal integration and turbulence modeling, capable of capturing the self-sustained oscillations characterizing stall flutter event with reasonable accuracy, including the mechanisms of energy transfer. [less ▲] Detailed reference viewed: 83 (13 ULg)Blowing against the tide Dimitriadis, Grigorios Article for general public (2011) Wind tunnels are experimental installations that create an airflow going past a test object. In a controlled and safe environment, they can recreate real-life situations, like an aircraft flying at 30 ... [more ▼] Wind tunnels are experimental installations that create an airflow going past a test object. In a controlled and safe environment, they can recreate real-life situations, like an aircraft flying at 30,000ft and 950km/h or a storm blasting a bridge deck. In this way the aerodynamic forces acting on structures can be measured, the flow-field around them can be visualised and fundamental research on aerodynamics can be carried out. Wind tunnels have been invaluable tools to aircraft, automobile and civil engineering designers for over 100 years. However, a significant number of wind tunnels have been decommissioned over the last 20 years, both in Europe and in the United States. Some of these closures have made the news, for instance the decommissioning of the NASA Ames facilities. There are many reasons for this phenomenon and a significant number of possible implications. [less ▲] Detailed reference viewed: 199 (8 ULg)Flapping flight aerodynamics for flying animals Norizham, Abdul Razak ; Dimitriadis, Grigorios Scientific conference (2011, October 10) Most research into the aerodynamics of flying animals is based on aircraft aerodynamics. Aircraft have rigid wings, therefore such research is mostly suited to the study of the gliding flight of animals ... [more ▼] Most research into the aerodynamics of flying animals is based on aircraft aerodynamics. Aircraft have rigid wings, therefore such research is mostly suited to the study of the gliding flight of animals. However, many species spend more time flapping than gliding. Some species don’t glide at all. This seminar presents recent work on flapping flight carried out at the University of Liège. [less ▲] Detailed reference viewed: 209 (6 ULg)Aerodynamic modeling of horizontal axis wind turbines Prasad, Chandra Shekhar ; Dimitriadis, Grigorios in Proceedings of the 13th International Conference on Wind Engineering (2011, July 14) The paper presents the development of a vortex lattice aerodynamic modeling routine for SAMCEF for Wind Turbine (S4WT). S4WT is a general-purpose commercial code for wind turbine design and analysis. At ... [more ▼] The paper presents the development of a vortex lattice aerodynamic modeling routine for SAMCEF for Wind Turbine (S4WT). S4WT is a general-purpose commercial code for wind turbine design and analysis. At present, it uses blade element momentum theory (BEM) for the estimation of the aerodynamics loads on HAWT rotor blades. BEM is a simple aerodynamic modeling approach that is currently used by several software packages for wind turbine design (as well as other rotor-based applications). It is based on the assumption that the flow can be treated as quasi-steady and quasi-2D, so that the steady, 2D aerodynamic loads acting on a strip of a rotor blade are used to estimate the instantaneous unsteady, 3D loads acting on a complete blade. This approach ignores the effect of the unsteady wake of the blades on the aerodynamic loads and simplifies the true 3D load distribution over the blades. A higher fidelity calculation of the time varying aerodynamic forces and moments acting on the blades is the main focus of this work. A good compromise between speed and accuracy to calculate these forces is the 3D unsteady vortex lattice method with a freely deforming wake. The vortex lattice results are compared to the BEM results from S4WT. The ultimate aim is to integrate the vortex lattice calculation as a subroutine in S4WT in order to calculate the unsteady aerodynamic forces on the rotor blades during the design process. This new method in S4WT will provide more representative results to the user, which can be very important for designing a more efficient wind turbine. [less ▲] Detailed reference viewed: 194 (9 ULg)Influence of a static wing wake on the stall flutter behavior of a flexible wing ; Dimitriadis, Grigorios in Proceedings of the 13th International Conference on Wind Engineering, ICWE13 (2011, July 13) The subject of this paper is the experimental study of the aeroelastic behavior of a wing undergoing stall flutter in the vicinity of second, static wing. While stall flutter has been the subject of ... [more ▼] The subject of this paper is the experimental study of the aeroelastic behavior of a wing undergoing stall flutter in the vicinity of second, static wing. While stall flutter has been the subject of several investigations, such work has almost always concentrated on isolated wings. Stall flutter is a phenomenon that is mostly encountered in rotating blades, such as wind turbine or helicopter blades. In such cases, the phenomenon is influenced by the wake of the preceding blade. This paper presents a series of experiments carried out at the Goldstein Laboratory of the University of Manchester, concerning the phenomenon of stall flutter influenced by the proximity of a static wing. The work is an extension of the single wing stall flutter experiments presented by Dimitriadis and Li (2009). [less ▲] Detailed reference viewed: 58 (1 ULg)Experimental Analysis of the Bifurcation Behaviour of a Bridge Deck Undergoing Across-Wind Galloping Andrianne, Thomas ; Dimitriadis, Grigorios in De Roeck, G.; Degrande, G.; Lombaert, G. (Eds.) et al Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011 (2011, July 05) The phenomenon of aeroelastic galloping is a very important design consideration for bridges and other slender structures. It has been investigated by a number of researchers but, most frequently, the ... [more ▼] The phenomenon of aeroelastic galloping is a very important design consideration for bridges and other slender structures. It has been investigated by a number of researchers but, most frequently, the analysis is limited to quasi-steady aerodynamic and linearized aeroelastic considerations. Such treatment has been shown to be effective for simple cross-sectional shapes, such as rectangles. In this work, an aeroelastic model of a realistic bridge deck cross-section is tested in a low speed wind tunnel. Both static and dynamic tests are carried out and the resulting force and vibration measurements are presented. The static force results are used to set up a quasi-steady mathematical model. The dynamic responses are used to draw a complete bifurcation diagram within a chosen airspeed range and to discuss the stability of the system. It is shown that the experimental system undergoes a subcritical Hopf bifurcation, its phase space including both a stable and an unstable limit cycle. As consequence, throughout the chosen airspeed, the system can either remain stable or undergo limit cycle oscillations. The quasi-steady analysis fails completely in capturing this type of behaviour. The predicted galloping onset speed is too conservative and the predicted oscillation amplitudes too high. The reason for this failure is the fact that the quasi-steady mathematical model is incapable of modelling subcritical Hopf bifurcations. [less ▲] Detailed reference viewed: 104 (21 ULg)Double wake vortex lattice modeling of horizontal axis wind turbines Prasad, Chandra Shekhar ; Dimitriadis, Grigorios in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2011 (2011, June 29) This paper presents the development of a vortex lattice based aerodynamic calculation for wind turbine blades. Emphasis is placed on the modeling of flow separation using the vortex lattice approach. This ... [more ▼] This paper presents the development of a vortex lattice based aerodynamic calculation for wind turbine blades. Emphasis is placed on the modeling of flow separation using the vortex lattice approach. This modeling is carried out by shedding a second free wake at the leading edge, which travels downstream at the local air velocity. The decision on whether to shed a wake or not is taken by looking at the sectional lift characteristics of the blade’s airfoil. If the local angle of attack exceeds the maximum lift angle, then a leading edge wake element is shed. Results from the method are presented for both attached and separated flow and compared with predictions obtained from the Blade Element Momentum theory. It is shown that the shedding of the leading edge wake can increased significantly the agreement between vortex lattice and Blade Element results in cases where there are significant regions of separated flow. This improvement concerns mostly forces acting normal to the rotor plane; tangential forces depend more strongly on the drag and neither method calculates a full representation of the drag. [less ▲] Detailed reference viewed: 83 (13 ULg)Wind tunnel analysis of separated aerodynamics leading to different types of torsional flutter in bluff-bodies. Andrianne, Thomas ; ; Dimitriadis, Grigorios in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2011 (2011, June 29) A new experimental apparatus has been developed at the wind tunnel laboratory of University of Liège with the objective to study the torsional flutter instability of a rectangular cylinder. Different ... [more ▼] A new experimental apparatus has been developed at the wind tunnel laboratory of University of Liège with the objective to study the torsional flutter instability of a rectangular cylinder. Different configurations, based on the position of the pitching axis, the stiffness of the restoring springs and the static equilibrium angle of the model have been tested and analysed. Sub- and supercritical bifurcations behaviour has been identified. The dynamics of the system, as well as the aerodynamic phenomena taking place around the model have been measured. The frequency content of the pitching displacement and the longitudinal component of the velocity in the wake showed the occurrence of two types of aerodynamic instability: large separation from the leading edge and vortex shedding in the Strouhal sense. Furthermore, preliminary Particle Image Velocimetry visualisation confirmed the presence of complex aerodynamic phenomena over the upper surface and in the wake of the model. These measurements allow a better understanding of the sources of aerodynamic excitation leading to torsional flutter. [less ▲] Detailed reference viewed: 89 (14 ULg)Interactive boundary layer calculation of separated flows around 2D airfoils Rothkegel Ide, José Ignacio ; Dimitriadis, Grigorios in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2011 (2011, June 27) Stall flutter is an important undesirable phenomenon affecting lifting surfaces such as helicopter and wind turbine blades, but is particularly difficult to model. Existing methodologies are not ... [more ▼] Stall flutter is an important undesirable phenomenon affecting lifting surfaces such as helicopter and wind turbine blades, but is particularly difficult to model. Existing methodologies are not universally applicable, and have significant limitations concerning applicability, time of computation and accuracy. This paper presents a method that combines interactive boundary layer with point vortex shedding. It is applied to a NACA0012 airfoil, at different angles of attack in the −40◦ < a < 40◦ range, considering a free flow velocity of 20[m/s]. Results are compared to those obtained at the Goldstein Laboratory of the University of Manchester. [less ▲] Detailed reference viewed: 47 (6 ULg)Wind tunnel experiments on a flapping drone Norizham, Abdul Razak ; Dimitriadis, Grigorios in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2011 (2011, May 29) The motivation for this paper is to obtain a better understanding of the unsteady aerodynamic phenomena involved in flapping wing flight. The work is mainly experimental but also makes use of numerical ... [more ▼] The motivation for this paper is to obtain a better understanding of the unsteady aerodynamic phenomena involved in flapping wing flight. The work is mainly experimental but also makes use of numerical results obtained from a vortex lattice approach. The flapping of 3D wings produces vortical structures which differ from those produced in 2D flow. It is a phenomenon experienced by any 3D lifting surfaces that are undergoing time dependent motion. In avian flight, it is known that different types of kinematics produce different kinds of vortical wake structures, depending on the wing aspect ratio. Understanding the wake structures and their effects can lead to the optimisation of flapping flight through the manipulation of these unsteady flow features. The objective of this work is to investigate the kinematics of 3D wings along with the evolution of the resulting vortex and wake structures while varying the oscillation parameters. The parameters in question are reduced frequency, flapping and pitching kinematics and wing profiles.The experiments make use of an enhanced version of a dynamically scaled mechanical flapping wing, which is modelled on large migrating birds with simplified kinematics. Pure flapping and combined pitching and flapping are tested in the wind tunnel and simulated at 6.0m/s, 9.4m/s and 14.8m/s.The model is forced to oscillate at four different frequencies. [less ▲] Detailed reference viewed: 90 (4 ULg)Complete bifurcation behaviour of aeroelastic systems with freeplay Dimitriadis, Grigorios in Proceedings of the 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2011, April) Over the last couple of decades, a significant amount of research has been carried out on the aeroelastic behaviour of aeroelastic systems with freeplay. It has been established that such systems can ... [more ▼] Over the last couple of decades, a significant amount of research has been carried out on the aeroelastic behaviour of aeroelastic systems with freeplay. It has been established that such systems can undergo Limit Cycle Oscillations (LCO), both periodic and aperiodic. It has also been shown that several LCOs can occur at the same flight conditions, depending on initial conditions. A lot of the work has been applied to a pitch-plunge airfoil with a control surface and freeplay in the control rotation spring but, even for this simple model, the complete LCO behaviour has not been calculated. In this work, a combined approach using equivalent linearization, a shooting-based numerical continuation scheme and branch following is used to calculate the full bifurcation behaviour of such a system. It is shown that the primary LCO branches depend on the underlying linear systems but that there are two branching points from which secondary periodic solution branches emanate and wrap themselves around the primary branches. Up to 13 different LCOs can coexist at a single flight condition. The system undergoes Hopf, fold, flip and Neimark-Sacker bifurcations and the proposed solution method can identify and all of them. [less ▲] Detailed reference viewed: 25 (0 ULg)A potential role for bat tail membranes in flight control ; Dimitriadis, Grigorios ; et al in PLoS ONE (2011), 6(3), 18214 Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus, indicated that the position of the tail membrane (uropatagium) can significantly influence flight control. Adjusting ... [more ▼] Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus, indicated that the position of the tail membrane (uropatagium) can significantly influence flight control. Adjusting tail position by increasing the angle of the legs relative to the body, has a two-fold effect; increasing leg-induced wing camber (i.e. locally increased camber and angle of attack of the inner wing surface) and increasing the angle of attack of the tail membrane. We also used our model to examine the effects of flying with and without a tail membrane. For the bat model with a tail membrane increasing leg angle increased the lift, drag and nose-down pitching moment produced. However, removing the tail membrane significantly reduced the change in pitching moment with increasing leg angle, but it had a much smaller effect on the level of lift and drag produced. The tail membrane, therefore, is potentially important for controlling the level of pitching moment produced by bats and an aid to flight control, specifically improving agility and manoeuvrability. Although the tail of bats is different from that of birds, in that it is only divided from the wings by the legs, it nonetheless, may, in addition to its prey capturing function, fulfil a similar role in aiding flight control. [less ▲] Detailed reference viewed: 79 (12 ULg)Flow Visualization and Proper Orthogonal Decomposition of Aeroelastic Phenomena Andrianne, Thomas ; Norizham, Abdul Razak ; Dimitriadis, Grigorios in Okamoto, Satoru (Ed.) Wind Tunnels (2011) The modal decomposition of unsteady flowfields was proposed in the 1990s by several authors. Proper Orthogonal Decomposition (POD) is one method that can be used in order to perform this modal ... [more ▼] The modal decomposition of unsteady flowfields was proposed in the 1990s by several authors. Proper Orthogonal Decomposition (POD) is one method that can be used in order to perform this modal decomposition; it became popular for aerodynamics research in the 2000s, although it was first proposed for use in fluid dynamics in the 1960s. The objective of the present work is to expand the methodology of the application of POD to experimental flowfields. There are two aspects to this expansion: 1. Allow the models to oscillate. The source of the unsteadiness will then be the movement of the model, as well as any unsteadiness due to flow separation. 2. Study the interaction between the different sources of unsteadiness. In particular observe how the modes generated by one source of unsteadiness interact with the modes generated by the other. Determine if it is possible to separate the structural from the aerodynamic sources of unsteadiness. [less ▲] Detailed reference viewed: 141 (30 ULg)Flutter and stall flutter of a rectangular wing in a wind tunnel Norizham, Abdul Razak ; Andrianne, Thomas ; Dimitriadis, Grigorios in AIAA Journal (2011), 49(10), 2258-2271 The aeroelastic behavior of a rectangular wing with pitch and plunge degrees of freedom was observed experimentally using pressure, acceleration and PIV measurements. The wing was set at different static ... [more ▼] The aeroelastic behavior of a rectangular wing with pitch and plunge degrees of freedom was observed experimentally using pressure, acceleration and PIV measurements. The wing was set at different static angles of attack and wind tunnel airspeeds. The wing's dynamic behavior was governed by a two-parameter bifurcation from steady to Limit Cycle Oscillations (LCO), the two parameters being the airspeed and the static angle of attack. At the lowest static angle, the wing underwent a classical flutter phenomenon that was transformed into a supercritical Hopf bifurcation at higher angles. The latter was combined with a fold bifurcation at intermediate angles of attack. All LCOs observed were either low amplitude oscillations with time-varying amplitude or high amplitude oscillations with nearly steady amplitude. They were caused by two different types of dynamic stall phenomena. During low amplitude LCOs the periodically stalled flow covered only the rear part of the wing. During high amplitude LCOs, trailing edge and leading edge separation occured. Trailing edge separation was characterized by a significant amount of unsteadiness, varying visibly from cycle to cycle. The occurrence of leading edge separation was much more regular and had the tendency to stabilize the amplitude of the LCO motion. [less ▲] Detailed reference viewed: 245 (45 ULg)Subcritical, nontypical and period doubling bifurcations of a Delta Wing in a low speed wind tunnel ; Kagambage, Emile ; Andrianne, Thomas et al in Journal of Fluids & Structures (2011), 27(3), 408-426 Limit Cycle Oscillations (LCOs) involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric or aerodynamic nonlinearity. In this paper ... [more ▼] Limit Cycle Oscillations (LCOs) involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric or aerodynamic nonlinearity. In this paper, a flexible half-span Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. The wing is designed to be more flexible than the models used in previous research on the subject in order to expand the airspeed range in which LCOs occur. The experiments reveal that this wing features a very rich bifurcation behavior. Three types of bifurcation are observed for the first time for such an aeroelastic system: subcritical bifurcations, period doubling/period halving and nontypical bifurcations. They give rise to a great variety of LCOs, even at very low angles of attack.The LCOs resulting from the nontypical bifurcation display Hopf-type behavior, i.e. have fundamental frequencies equal to one of the linear modal frequencies. All of the other LCOs have fundamental frequencies that are unrelated to the underlying linear system modes. [less ▲] Detailed reference viewed: 79 (23 ULg)Shooting-Based Complete Bifurcation Prediction for Aeroelastic Systems with Freeplay Dimitriadis, Grigorios in Journal of Aircraft (2011), 48(6), 1864-1877 In recent years there have been several applications of numerical continuation approaches to aeroelastic systems with freeplay. While some of these have been successful, the general application of the ... [more ▼] In recent years there have been several applications of numerical continuation approaches to aeroelastic systems with freeplay. While some of these have been successful, the general application of the method to such systems remains problematic. Numerical continuation can fail in the presence of complex bifurcations, numerous nearby periodic solution branches and other factors. In this paper, a three-part procedure for applying numerical continuation to aeroelastic systems with freeplay is proposed, designed to ensure that the complete periodic behavior is identified, even for systems with very complex bifurcation diagrams. First, the equivalent linearization approach is used to determine approximations to the periodic solutions of the nonlinear system. Then, a shooting-based technique is applied separately to each linearized approximation in order to pinpoint the nearest exact periodic solution. This process results in a cloud of periodic solutions, representing points on all the solution branches and sub-branches. Finally, a branch-following shooting procedure is applied to this cloud of points in order to obtain a complete description of every branch of periodic solutions. The methodology is applied to a simple aeroelastic system with three degrees of freedom and freeplay in the control surface. This system has been often studied but never fully characterised. It is shown that the proposed method succeeds in describing the complete bifurcation behaviour of the system and explaining its limit cycle response. [less ▲] Detailed reference viewed: 36 (5 ULg)Determination of the complete bifurcation behaviour of aeroelastic systems with freeplay Dimitriadis, Grigorios Scientific conference (2010, November 09) In recent years there have been several applications of the nonlinear numerical continuation approach to aeroelastic systems with freeplay. While some of these have been successful, the general ... [more ▼] In recent years there have been several applications of the nonlinear numerical continuation approach to aeroelastic systems with freeplay. While some of these have been successful, the general application of the method to such systems remains problematic. Numerical continuation can fail in the presence of complex bifurcations, numerous nearby periodic solution branches and other factors. In this paper, a three-part procedure for applying numerical continuation to aeroelastic systems with freeplay is proposed, designed to ensure that the complete periodic behavior is identified, even for systems with complex bifurcation diagrams. First, the equivalent linearization approach is used to determine approximations to the periodic solution branches of the nonlinear system. Then, a shooting-based technique is applied separately to each linearized approximation in order to pinpoint the nearest exact periodic solution. This process results in a cloud of periodic solutions, representing all the branches and sub-branches. Finally, a branch-following shooting procedure is applied to this cloud of points in order to obtain a complete description of every branch of periodic solutions. The procedure is demonstrated on a simple 3-DOF mathematical aeroelastic system with freeplay; it is shown that an extremely complex bifurcation is fully captured. The system's bifurcation diagram features multiple branch crossings, folds and loops. Its complete calculation allows the justification of several interesting LCO phenomena, such as aperiodic LCOs. [less ▲] Detailed reference viewed: 33 (5 ULg)Limit Cycle Oscillations of a Delta Wing in a Low Speed Wind Tunnel ; Kagambage, Emile ; Andrianne, Thomas et al in Proceedings of ISMA2010 (2010, September 22) Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a ... [more ▼] Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a flexible half-Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. Specifically, an investigation to determine the effects of a steady angle of attack on nonlinear Limit Cycle Oscillations (LCO) of a delta wing-plate model in low subsonic flow has been undertaken. It was found that, at several combinations of airspeed and angle of attack, the wing undergoes limit cycle oscillations. Two types of such oscillations are observed. One of them is low amplitude, low complexity limit cycle oscillations that occur at lower airspeeds; the other is high amplitude, high complexity limit cycle oscillations that occur a higher airspeeds and can appear abruptly. Some of the LCOs are the result of a subcritical Hopf bifurcation occurring at low steady angles of attack. At higher angles, a nontypical bifurcation was observed, whereby LCOs appear, grow with airspeed but then diminish and finally disappear as the airspeed is increased further. [less ▲] Detailed reference viewed: 86 (29 ULg)Bifurcation analysis of a wing undergoing stall flutter oscillations in a wind tunnel Norizham, Abdul Razak ; Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of ISMA2010 (2010, September 20) Stall flutter is a Limit Cycle Oscillation (LCO) caused by the periodic separation of the flow around a wing immersed in a uniform fluid flow. The separation could be either partial or complete [1]. The ... [more ▼] Stall flutter is a Limit Cycle Oscillation (LCO) caused by the periodic separation of the flow around a wing immersed in a uniform fluid flow. The separation could be either partial or complete [1]. The work presented focuses on a wing undergoing stall flutter in the pitch degree of freedom. The phenomenon is analyzed from the structural and aerodynamic response perspectives. The objective of this study is to promote the understanding of stall flutter by characterizing the complete bifurcation behavior of the selected system. The wing section chosen for this study is NACA 0018 profile applied to a rectangular wing. The tests are carried out at different airspeeds and angles of attack. The measured aeroelastic responses are analyzed and the behavior of the dynamic system is characterized by fully describing its bifurcation. Structural accelerations as well as unsteady pressures around the mid-span point of the wing are measured and examined. Furthermore, flow field visualization by means of the Particle Image Velocimetry technique is used to demonstrate aspects of the unsteady flow field, such as the manifestation of separation and vortices. [less ▲] Detailed reference viewed: 108 (11 ULg) |
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