References of "Norizham, Abdul Razak"
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See detailAeroelastic response of a 2-DOF wing with structural and aerodynamic nonlinearity
Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2013 (2013, June 25)

The aeroelastic behaviour of a wing oscillating in the heave and pitch degrees of freedom with continuos nonlinear stiffness is examined by means of wind tunnel experiments. The phenomena of interest are ... [more ▼]

The aeroelastic behaviour of a wing oscillating in the heave and pitch degrees of freedom with continuos nonlinear stiffness is examined by means of wind tunnel experiments. The phenomena of interest are classical flutter and limit cycle oscillation. The focus of the present work is the transformation of classical flutter into LCOs by varying the stiffness from linear to nonlinear stiffness. The interaction of flow separation-related nonlinearity with structural nonlinearities is also of interest. The measured aeroelastic responses are analyzed and the bifurcation behavior of the dynamic system is characterized. The analysis shows that the bifurcation behaviour is dictated neither by the structural nor from the aerodynamic nonlinearity but by a combination of the two. [less ▲]

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See detailSimulation of bird wing flapping using the unsteady vortex lattice method
Gardiner, James; Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2013 (2013, June 24)

The flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three ... [more ▼]

The flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three barnacle geese flying at different airspeeds in a wind tunnel. The video footage was analysed in order to extract the wing kinematics. Additional information, such as wing geometry and camber was obtained from a 3D scan of a dried wing. An unsteady vortex lattice method was used to simulate the aerodynamics of the measured flapping motion. It was found that the simulation correctly predicted the shape of the wake and the fact that the wing is aerodynamically inactive during the upstroke. The predicted aerodynamic lift and thrust forces were very sensitive to the wing's camber. Future work will attempt to identify the sensitivity to all the wing shape and kinematic parameters. Additional phenomena will also be modelled, including passive twisting of the wingtip, body lift and leading edge suction. [less ▲]

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See detailExperimental Investigation of the Aerodynamics and Aeroelasticity of Flapping, Plunging and Pitching Wings
Norizham, Abdul Razak ULg

Doctoral thesis (2012)

This thesis concerns the experimental analysis of the aerodynamics and aeroelasticity of oscillating wings. It is divided into two sections, an inves- tigation of wings undergoing imposed root flapping ... [more ▼]

This thesis concerns the experimental analysis of the aerodynamics and aeroelasticity of oscillating wings. It is divided into two sections, an inves- tigation of wings undergoing imposed root flapping and pitching motion, such as seen in avian flight and an experimental investigation of the self- excited stall flutter oscillations of a wing undergoing plunging and pitching motion. The objective of the flapping wing investigation is to improve the under- standing of the unsteady aerodynamics of flapping flight. The work con- sists of designing and building a flapping and pitching bird-like mechanical model and testing it in a low speed wind tunnel. The model’s size is sim- ilar to that of a goose. The wind tunnel tests involved the measurement of forces, power, kinematics and local flow velocities using Particle Im- age Velocimetry (PIV). The mechanical model was tested at four different frequencies and three airspeeds. In addition, three different wing profiles were tested. The kinematic modes included pure flapping and combined flapping and pitching. It was shown that pure flapping and pitch-lagging combined motion can lead to interesting aerodynamic phenomena, such as flow separation and dynamic stall. Dynamic stall can cause significant increases in instantaneous lift production, although it also generates a lot of drag. On the contrary, pitch leading combined motion can generate a net propulsive force over the entire cycle. In the stall flutter study, a 6 degree of freedom NACA 0018 wing was sus- pended by springs in the wind tunnel. The wing was then exposed to an airflow at a number of airspeeds and wind-off angles of attack. The wing was instrumented with pressure sensors and accelerometers. In addition, PIV flow measurements were carried out on the wing’s upper surface. The work demonstrates that stall flutter is the result of a combination of dy- namic stall with the elastic properties of the system. The dynamic stall mechanism was studied using the PIV measurements and was found to be different to the classical stall mechanisms that are reported in the litera- ture. The sensitivity of the stall flutter phenomenon to parameters such as airspeed and wind-off angle of attack is demonstrated by means of a two-parameter bifurcation diagram. [less ▲]

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See detailExperiments on a pitch-plunge wing undergoing limit cycle oscillation
Norizham, Abdul Razak ULg; Rothkegel Ide, José Ignacio ULg; Dimitriadis, Grigorios ULg

in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 25)

The aeroelastic behaviour of a wing oscillating in the heave and pitch degrees of freedom is examined by means of wind tunnel experiment. The phenomena of interest are classical flutter and limit cycle ... [more ▼]

The aeroelastic behaviour of a wing oscillating in the heave and pitch degrees of freedom is examined by means of wind tunnel experiment. The phenomena of interest are classical flutter and limit cycle oscillation. Classical flutter is normally associated with the exponential growth of the response amplitude. Linear flutter theory only predicts the critical flutter speed. Any excitation or disturbance beyond the critical speed is assumed to cause exponential growth in the response amplitude. In contrast, any limited amplitude oscillations occurring post-fultter suggest the existence of nonlinear properties in the system. Such properties can originate from the aerodynamic forces in the form of flow separation and reattachment. On the structural side, damping and stiffness can also contribute nonlinear properties. Furthermore, these nonlinearities can manifest themselves even at pre-flutter conditions, depending on the values of some governing parameter. The focus of the present work is the transformation of classical flutter into stall flutter as the equilibrium angle of attack of heaving and pitching wing is increased. The interaction of stall-related nonlinearity with structural nonlinearities is also of interest. The measured aeroelastic responses are analyzed and the bifurcation behavior of the dynamic system is characterized. Structural responses as well as flow field visualization through Particle Image Velocimetry show the origin of nonlinearity does not solely come from the manifestation of separation and the shedding of vortices, but from the structural nonlinearity which limits the response amplitude. [less ▲]

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See detailA Cross-Validation Approach to Approximate Basis Function Selection of the Stall Flutter Response of a Rectangular Wing in a Wind Tunnel
Kukreja, Sunil L.; Vio, Gareth A.; Andrianne, Thomas ULg et al

in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 25)

The stall flutter response of a rectangular wing in a low speed wind tunnel is modelled using a nonlinear difference equation description. Static and dynamic tests are used to select a suitable model ... [more ▼]

The stall flutter response of a rectangular wing in a low speed wind tunnel is modelled using a nonlinear difference equation description. Static and dynamic tests are used to select a suitable model structure and basis function. Bifurcation criteria such as the Hopf condition and vibration amplitude variation with airspeed were used to ensure the model was representative of experimentally measured stall flutter phenomena. Dynamic test data were used to estimate model parameters and estimate an approximate basis function. [less ▲]

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See detailFlapping flight aerodynamics for flying animals
Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg

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 ▲]

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See detailWind tunnel experiments on a flapping drone
Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg

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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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See detailTransonic Limit Cycle Oscillation Prediction From Simulated In-Flight Data
Norizham, Abdul Razak ULg; Dimitriadis, Grigorios ULg

in Proceedings of the 2008 International Conference on Noise and Vibration Engineering (2008, September)

This paper investigates the transonic Limit Cycle Oscillation (LCO) phenomenon from a computational/simulation point of view. A CFD/FE coupled solution is applied to a 3D model of a rectangular wing with ... [more ▼]

This paper investigates the transonic Limit Cycle Oscillation (LCO) phenomenon from a computational/simulation point of view. A CFD/FE coupled solution is applied to a 3D model of a rectangular wing with tip store (referred to as the Goland wing) in transonic flow, in order to study the resulting LCO motions. The aim of the study is to develop a LCO prediction strategy from in-flight data; at this stage of the work the data will be obtained from simulations. The effect of varying the thickness of the Goland wing on the LCO onset flight condition is explored. The work then addresses the presence or absence of nonlinearity prior to the onset of LCOs. This is crucial as the presence of any nonlinearity for this type of wing can act as a telltale sign of impending LCOs. The clearance between the nonlinearity onset flight condition and the LCO onset flight condition is quantified for various values of the wing design parameters. It is shown that this clearance can be used in order to develop a useful ‘oncoming LCO’ warning criterion. [less ▲]

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