References of "Dimitriadis, Grigorios"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailA potential role for bat tail membranes in flight control
Gardiner, James D; Dimitriadis, Grigorios ULg; Codd, Jonathan R 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: 69 (12 ULg)
Full Text
See detailFlow Visualization and Proper Orthogonal Decomposition of Aeroelastic Phenomena
Andrianne, Thomas ULg; Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg

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: 92 (25 ULg)
Full Text
Peer Reviewed
See detailFlutter and stall flutter of a rectangular wing in a wind tunnel
Norizham, Abdul Razak ULg; Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

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: 187 (37 ULg)
Full Text
Peer Reviewed
See detailSubcritical, nontypical and period doubling bifurcations of a Delta Wing in a low speed wind tunnel
Korbahti, Banu; Kagambage, Emile ULg; Andrianne, Thomas ULg 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: 58 (21 ULg)
Full Text
Peer Reviewed
See detailShooting-Based Complete Bifurcation Prediction for Aeroelastic Systems with Freeplay
Dimitriadis, Grigorios ULg

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: 24 (3 ULg)
Full Text
See detailDetermination of the complete bifurcation behaviour of aeroelastic systems with freeplay
Dimitriadis, Grigorios ULg

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: 30 (4 ULg)
Full Text
See detailLimit Cycle Oscillations of a Delta Wing in a Low Speed Wind Tunnel
Korbahti, Banu; Kagambage, Emile ULg; Andrianne, Thomas ULg 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: 81 (28 ULg)
Full Text
See detailBifurcation analysis of a wing undergoing stall flutter oscillations in a wind tunnel
Norizham, Abdul Razak ULg; Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

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: 91 (9 ULg)
Full Text
See detailDamping identification in a non-linear aeroelastic structure
Vio, Gareth A.; Prandina, Marco; Dimitriadis, Grigorios ULg

in Proceedings of ISMA2010 (2010, September 20)

An energy-based method is proposed to identify damping parameters from time histories of responses to sets of single-frequency harmonic excitation. The method is intended to be practically applicable to ... [more ▼]

An energy-based method is proposed to identify damping parameters from time histories of responses to sets of single-frequency harmonic excitation. The method is intended to be practically applicable to real structures and is able to identify the value of viscous damping, Coulomb friction and eventually other forms of non-linear damping models in aeroelastic systems. The inputs required are simply the accelerometer signals and the forces applied. It will be shown that if the system is undergoing Limit Cycle Oscillations, no external force is required for the identification process. [less ▲]

Detailed reference viewed: 48 (7 ULg)
Full Text
See detailDevelopment and Evaluation of a VTOL Observation Platform
Buysschaert, F.; Yacoubi, M.; Alami, A. et al

in Proceedings of the 27th International Congress of the Aerospace Sciences (2010, September)

An aerodynamic study of the ULB-developed ducted rotor MAV using the results of full-scale wind tunnel tests allowed the determination of the platform’s positive speed envelope, power requirements and ... [more ▼]

An aerodynamic study of the ULB-developed ducted rotor MAV using the results of full-scale wind tunnel tests allowed the determination of the platform’s positive speed envelope, power requirements and endurance characteristics for ISA sea level conditions. In this study, the power consumption appears to be majorly depending on the rotor rotational speed, while an increase in horizontal speed results in a duct operating more as a circular wing, also unveiling a power bucket as is the case with conventional helicopters. A positive influence of the ground proximity on the total thrust has been monitored. [less ▲]

Detailed reference viewed: 55 (17 ULg)
Full Text
See detailEtude du comportement aéroélastique des structures soumises à des écoulements décrochés
Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

Conference (2010, March 02)

L'objectif du travail de recherche est le développement d'un modèle numérique simulant les phénomènes aéroélastiques affectant les corps non-profilés, caractérisés par des effets de décrochage/raccrochage ... [more ▼]

L'objectif du travail de recherche est le développement d'un modèle numérique simulant les phénomènes aéroélastiques affectant les corps non-profilés, caractérisés par des effets de décrochage/raccrochage du fluide.L'application de ce modèle aux tabliers de point est prévue. [less ▲]

Detailed reference viewed: 65 (23 ULg)
Full Text
See detailProper Orthogonal Decomposition of Unsteady Aerodynamic Flows
Andrianne, Thomas ULg; Ligot, Jerome; Dimitriadis, Grigorios ULg

Report (2009)

This work constitutes the final report for a project funded by the Fonds de la Recherche Scientifique. The objective of the project was to acquire and install Par- tical Image Velocimetry (PIV) hardware ... [more ▼]

This work constitutes the final report for a project funded by the Fonds de la Recherche Scientifique. The objective of the project was to acquire and install Par- tical Image Velocimetry (PIV) hardware in the University of Liege Wind Tunnel facility in order to carry out the Proper Orthogonal Decomposition (POD) of un- steady aerodynamic flows. The characteristics and installation of the PIV system are described in the present report. Furthermore, the application of POD analysis to three different visualized flow cases is detailed. The flow cases were: flow be- hind a circular cylinder and separated flow over a rectangular wing. In all cases, emphasis was given to the combination of unsteadiness caused by both boundary layer separation and movement of the wind tunnel model. It is shown that the de- composition of flowfields that combine these two sources of unsteadiness is possible and informative. [less ▲]

Detailed reference viewed: 107 (20 ULg)
Full Text
See detailAnalysis of dynamic response of a very flexible Delta wing model in a wind tunnel
Barbason, Mathieu ULg; Andrianne, Thomas ULg; Hickey, Daryl ULg et al

in Proceedings of the 2009 International Forum on Aeroelasticity and Structural Dynamics (2009, July)

Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric nonlin- earity, aerodynamic nonlinearity or under ... [more ▼]

Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric nonlin- earity, aerodynamic nonlinearity or under-wing store nonlinearity. In this paper, a flexible half-Delta wing without stores is tested in a low speed wind tunnel in order to investigate its dynamic response. It is found that, at several combinations of airspeed and angle of attack, the wing undergoes high amplitude limit cycle oscillations. Three types of such oscillations are observed. Type 1 oscillations occur only at low angles of attack and are the result of a Hopf-type bifurcation. Type 2 limit cycle oscillations occur at intermedi- ate angles of attack and are the result of an atypical bifurcation. In other words, these oscillations appear as the airspeed is increased but disappear at even higher airspeeds. Type 3 oscillations occur at even higher angles of attack. A bispectrum analysis shows that type 3 limit cycle oscillations feature quadratic phase coupling. No such coupling was measured for type 2 oscillations, leading to the conclusion that the nonlinearity must be of higher order. [less ▲]

Detailed reference viewed: 95 (37 ULg)
Full Text
See detailA Novel Concept for Helicopter Rotor Drives
Antoine, Hubert; Dimitriadis, Grigorios ULg; Hendrick, Patrick et al

in Proceedings of the 3rd European Conference for Aero-Space Sciences (2009, July)

The REDT (Rotor à Entraînement Direct par Turbine – Direct Turbine Driven Rotor) is a new concept for helicopter rotor drives developed by Sagita in Belgium. It works without any mechanical link between ... [more ▼]

The REDT (Rotor à Entraînement Direct par Turbine – Direct Turbine Driven Rotor) is a new concept for helicopter rotor drives developed by Sagita in Belgium. It works without any mechanical link between the engine on one side and the rotor drive on the other side. It uses a fuselage-mounted compressor that powers two contra-rotating rotor-mounted free turbines. These free turbines drive a pair of contrarotating rotors that are fitted with rigid hingeless main rotor blades. This novel rotor drive eliminates the need for either mechanical transmission or a tail rotor. The aim of the REDT concept is to lower the maintenance costs and the accident rate, as well as to extend the flight envelope towards much higher airspeeds compared to classical helicopters. [less ▲]

Detailed reference viewed: 380 (17 ULg)
Full Text
See detailExperiments on a 3-D Flapping and Pitching Mechanical Model
Norizham, Abdul Razak ULg; Rothkegel Ide, José Ignacio ULg; Dimitriadis, Grigorios ULg

in Proceedings of the 2009 International Forum on Aeroelasticity and Structural Dynamics (2009, June)

The motivation for this paper is to focus on the better understanding of flapping wing flight, including flapping flight involving high pitching amplitudes. The investigation will be primarily ... [more ▼]

The motivation for this paper is to focus on the better understanding of flapping wing flight, including flapping flight involving high pitching amplitudes. The investigation will be primarily experimental. The experiment will utilize a mechanical flapping and pitching wind tunnel model, which is modeled on large migrating birds. The 3-D rectangular wings are forced to flap and pitch sinusoidally in a low speed wind tunnel. The unsteady aerodynamic forces generated are measured using a three-component force balance. The main objective of this work is to investigate the effect that varying the oscillation parameters has on the aerodynamic forces acting on the 3-D wing undergoing flapping and pitching. The parameters in question are reduced frequency, flapping ampli- tude and pitching amplitude. Comparisons are made with aerodynamic force predictions obtained from unsteady vortex lattice calculations. [less ▲]

Detailed reference viewed: 93 (7 ULg)
Full Text
See detailUsing the Discrete Vortex Method to Simulate the Stall Flutter Phenomenon
Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

in Proceedings of the 2009 International Forum on Aeroelasticity and Structural Dynamics (2009, June)

The Discrete Vortex Method (DVM) has been recently used by several researchers in order to simulate the dynamic stall phenomenon on 2D airfoils oscillating at high angles of attack or undergoing stall ... [more ▼]

The Discrete Vortex Method (DVM) has been recently used by several researchers in order to simulate the dynamic stall phenomenon on 2D airfoils oscillating at high angles of attack or undergoing stall flutter oscillations. The aim of the present work is to investigate whether such simulations are representative of the true physics governing such oscillation. A DVM method is described and implemented. A basic validation of the method is performed on the case of an impulsively started static airfoil at a low angle of attack. It is shown that the steady state lift value obtained from the DVM method agrees with experimental measurements. Subsequently, a DVM simulation is performed for the case of a NACA 0012 airfoil undergoing symmetric stall flutter oscillations. The simulation results are compared to experimental results. It is shown that, while the general shape of the simulated lift variation with time agrees with the experiment, there are significant mean value and phase differences between experiment and simulation. Several justifications are suggested and improvements to the DVM simulation proposed. [less ▲]

Detailed reference viewed: 130 (17 ULg)
Full Text
See detailWind tunnel investigation of the stall flutter oscillations of a bridge deck
Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

in Proceedings of the 8th National Congress on Theoretical and Applied Mechanics (2009, May)

Torsional Stall Flutter (TSF) is a one degree of freedom, self-excited phenomenon induced by the periodic separation/re-attachment of the flow around a body. The present paper proposes an experimental ... [more ▼]

Torsional Stall Flutter (TSF) is a one degree of freedom, self-excited phenomenon induced by the periodic separation/re-attachment of the flow around a body. The present paper proposes an experimental investigation of TSF on a bridge deck. A section model free to oscillate in torsion is tested in a low-speed wind tunnel. Static and dynamic tests are performed to enable a complete interpretation of the phenomena involved. For low airspeeds, the Karman vortex shedding excites the structure, resulting in small oscillations at the vortex shedding frequency. For high airspeeds, the deck undergoes Limit Cycle Oscillations (LCO) due to the TSF phenomenon. Nevertheless the Karman vortex shedding excitation is still present and appears in the measured forces signals. Peaks and troughs in the lift coefficient are detected for each pitching period. They are interpreted as the separation/re-attachment of the flow around the deck. The large amplitudes motion of the deck undergoing TSF reduces the amplitude of the aerodynamic lift coefficient. [less ▲]

Detailed reference viewed: 56 (13 ULg)
Full Text
Peer Reviewed
See detailIdentification of a Nonlinear Wing Structure Using an Extended Modal Model
Platten, M. F.; Wright, J. R.; Cooper, J. E. et al

in Journal of Aircraft (2009), 46(5), 1614-1626

The nonlinear resonant decay method identifies a nonlinear dynamic system using a model based in linear modal space comprising the underlying linear system and a small number of additional terms that ... [more ▼]

The nonlinear resonant decay method identifies a nonlinear dynamic system using a model based in linear modal space comprising the underlying linear system and a small number of additional terms that represent the nonlinear behavior. In this work, the method is applied to an aircraftlike wing/store/pylon experimental structure that consists of a rectangular wing with two stores suspended beneath it by means of nonlinear pylons with a nominally hardening characteristic in the store rotation degree of freedom. The nonlinear resonant decay method is applied to the system using multishaker excitation. The resulting identified mathematical model features five modes, two of which are strongly nonlinear, one is mildly nonlinear, and two are completely linear. The restoring force surfaces obtained from the mathematical model are in close agreement with those measured from the system. This experimental application of the nonlinear resonant decay method indicates that the method could be suitable for the identification of nonlinear models of aircraft in ground vibration testing. [less ▲]

Detailed reference viewed: 59 (11 ULg)
Full Text
Peer Reviewed
See detailIdentification of multi-degree of freedom non-linear systems using an extended modal space model
Platten, Michael F; Wright, Jan Robert; Dimitriadis, Grigorios ULg et al

in Mechanical Systems & Signal Processing (2009), 23(1), 8-29

The identification of non-linear dynamic systems is an increasingly important area of research, with potential application in many industries. Current non-linear identification methodologies are, in ... [more ▼]

The identification of non-linear dynamic systems is an increasingly important area of research, with potential application in many industries. Current non-linear identification methodologies are, in general, mostly suited to small systems with few degrees of freedom and few non-linearities. In order to develop a practical identification approach for real engineering structures, the capability of such methods must be significantly extended. In this paper, it is shown that such an extension can be achieved using multi-exciter techniques in order to excited specific modes or degrees of freedom of the system under investigation. A novel identification method for large non-linear systems is presented, based on the use of a multi-exciter arrangement using appropriated excitation applied in bursts. This proposed Non-linear Resonant Decay Method is applied to a simulated system with 5 degrees of freedom and an experimental clamped panel structure. The technique is essentially a derivative of the Restoring Force Surface method and involves a non-linear curve fit performed in modal space. The effectiveness of the resulting reduced order model in representing the non-linear characteristics of the system is demonstrated. The potential of the approach for the identification of large continuous non-linear systems is also discussed. [less ▲]

Detailed reference viewed: 107 (11 ULg)
Full Text
Peer Reviewed
See detailBifurcation Behavior of Airfoil Undergoing Stall Flutter Oscillations in Low-Speed Wind Tunnel
Dimitriadis, Grigorios ULg; Li, Jing

in AIAA Journal (2009), 47(11), 2577-2596

Stall flutter is a nonlinear aeroelastic phenomenon that can affect several types of aeroelastic systems such as helicopter rotor blades, wind turbine blades, and highly flexible wings. Although the ... [more ▼]

Stall flutter is a nonlinear aeroelastic phenomenon that can affect several types of aeroelastic systems such as helicopter rotor blades, wind turbine blades, and highly flexible wings. Although the related aerodynamic phenomenon of dynamic stall has been the subject of many experimental studies, stall flutter itself has rarely been investigated. This paper presents a set of experiments conducted on a NACA0012 airfoil undergoing stall flutter oscillations in a low-speed wind tunnel. The aeroelastic responses are analyzed with the objective of characterizing the local bifurcation behavior of the system. It is shown that symmetric stall flutter oscillations are encountered as a result of a subcritical Hopf bifurcation, followed by a fold bifurcation. The cause of these bifurcations is the occurrence of dynamic stall, which allows the transfer of energy from the freestream to the wing. A second bifurcation occurs at the system’s static divergence airspeed. As a consequence, the wing starts to undergo asymmetric stall flutter bifurcations at only positive (or only negative) pitch angles. The dynamic stall mechanism itself does not change but the flow only separates on one side of the wing. [less ▲]

Detailed reference viewed: 116 (12 ULg)