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Experimental and numerical investigations of the torsional flutter oscillations of a 4:1 rectangular cylinder Andrianne, Thomas ; Dimitriadis, Grigorios in Journal of Fluids & Structures (2013), 41 The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different ... [more ▼] The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different initial conditions and turbulence excitations at various wind tunnel airspeeds are recorded. Timeresolved Particle Image Velocimetry measurements are taken at two different airspeeds, when the rectangle undergoes Limit Cycle Oscillations. Aeroelastic simulations are carried out using the Discrete Vortex Method and the resulting responses are compared to the experimental measurements. The Common-base Proper Orthogonal Decomposition method is used to analyse and compare the measured and simulated unsteady flow fields around the rectangle. A discussion of the participation of each mode in the different states of the flow-field is presented, at two different amplitudes of oscillation. The Motion Induced Vortex (MIV) is identified as the fundamental cause of the torsional flutter phenomenon and its role over a complete cycle is studied. MIV-induced oscillations can be started either by a suitable initial disturbance or by a second, nearly linear self-excited instability that causes negative aerodynamic damping. The combination of these two instabilities results in a complete description of the torsional flutter of the rectangle. [less ▲] Detailed reference viewed: 147 (41 ULg)Torsional flutter of bluff bodies Terrapon, Vincent ; Guissart, Amandine ; Andrianne, Thomas et al Scientific conference (2013, July 15) Detailed reference viewed: 49 (18 ULg)Dry galloping on bridge cables: roughness and shape effects on an inclined circular cylinder ; ; et al in Proceedings of the European-African Conference on Wind Engineering 2013 (2013, July 09) Dry galloping of stays in cable-stayed bridges is a phenomenon that is still of interest to the scientific community. Over the course of the current three-year research project numerous experiments will ... [more ▼] Dry galloping of stays in cable-stayed bridges is a phenomenon that is still of interest to the scientific community. Over the course of the current three-year research project numerous experiments will be carried out to investigate the effect of turbulence and inclination angle on dry galloping. The novel aspect of this study consists of an in-depth investigation into the effect of non uniformity of the pipe surrounding the stay cables on the dry galloping excitation mechanism. Previous studies reported that dry galloping is caused by the appearance of a negative pressure bubble on one side of the circular cylinder at the critical Reynolds number range, leading to a rapid drop in the drag coefficient and the appearance of a non negligible lift force. This paper presents results from initial experiments in the wind tunnel at CSTB – Nantes, France. [less ▲] Detailed reference viewed: 105 (3 ULg)Numerical and Experimental Investigation of Slot-Blowing Air Over a Cylinder ; ; et al in Proceedings of the 5th European Conference for Aeronautics and Space Sciences (2013, July) Tangential slot blowing around a cylinder in the Coanda effect has been proposed as a mechanism for yaw control in a novel coaxial helicopter. The proposed design has been investigated computationally ... [more ▼] Tangential slot blowing around a cylinder in the Coanda effect has been proposed as a mechanism for yaw control in a novel coaxial helicopter. The proposed design has been investigated computationally, using the unsteady k-ω SST solver in NUMECA, as well as experimentally in the wind tunnel at the Université de Liège. While the concept in general is promising, it has been shown that there are some potential problems, including pitch-yaw coupling and some unsteady flow conditions. These problems exist under varied circumstances, and, exist at least in part due to the complicated flow-field in this problem, even in 2-dimensions. [less ▲] Detailed reference viewed: 83 (24 ULg)Using Proper Orthogonal Decomposition and Dynamic Mode Decomposition Methods for Comparing CFD Results Experimental Measurements Guissart, Amandine ; Andrianne, Thomas ; Dimitriadis, Grigorios et al in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2013 (2013, June 26) A method for the quantitative comparison of numerical and/or experimental data of unsteady aerodynamics around static and oscillating bodies is introduced. It is based on Proper Orthogonal Decomposition ... [more ▼] A method for the quantitative comparison of numerical and/or experimental data of unsteady aerodynamics around static and oscillating bodies is introduced. It is based on Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) to extract the dominant structures of the unsteady flow. The proposed method is applied to spatio-temporal data for the flow around a 4:1 rectangular cylinder. Exper- imental data are obtained from wind tunnel testing and two dimensional Time-resolved Particle Image Velocimetry (Tr-PIV) measurements, while unsteady Reynolds Averaged Navier-Stokes (uRANS) are used to compute numerical results. It is demonstrated that the two approaches are complementary and represent a powerful tool that enables the analysis and the quantitative comparison of the main spatial (POD) and temporal (DMD) characteristics of unsteady aerodynamic data. [less ▲] Detailed reference viewed: 188 (55 ULg)Aeroelastic response of a 2-DOF wing with structural and aerodynamic nonlinearity Norizham, Abdul Razak ; Dimitriadis, Grigorios 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 ▲] Detailed reference viewed: 67 (3 ULg)Simulation of bird wing flapping using the unsteady vortex lattice method ; Norizham, Abdul Razak ; Dimitriadis, Grigorios 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 ▲] Detailed reference viewed: 233 (9 ULg)Dynamic Stall and Stall Flutter Simulations for a 2D Airfoil Using Viscous-Inviscid Coupling Rothkegel Ide, José Ignacio ; Dimitriadis, Grigorios in Proceedings of the 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2013, April 10) An interactive boundary layer model has been developed and coupled with a pitch plunge airfoil in 2d in order to solve the unsteady flow around the airfoil when undergoing light dynamic stall. The ... [more ▼] An interactive boundary layer model has been developed and coupled with a pitch plunge airfoil in 2d in order to solve the unsteady flow around the airfoil when undergoing light dynamic stall. The inviscid problem is solved by means of a panel method, by the discretization of the airfoil into vortex panels. The boundary layer is solved in a mixed manner, starting the solution in a direct way by imposing the external velocity and continuing it in an inverse way by imposing the displacement thickness. The solution of the boundary layer equations is carried out using a finite volume scheme. Viscous-inviscid coupling is preformed through the imposition of a permeation velocity on the skin panels of the airfoil and the addition of a free wake at each separation point. [less ▲] Detailed reference viewed: 89 (15 ULg)Integrating Experimental and Computational Fluid Dynamics approaches using Proper Orthogonal Decomposition Techniques Andrianne, Thomas ; ; Guissart, Amandine et al in Progress in Aerospace Sciences (2013) The concept of Proper Orthogonal Decomposition (POD) is used to integrate Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) approaches. The key idea is to take advantage of the ... [more ▼] The concept of Proper Orthogonal Decomposition (POD) is used to integrate Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) approaches. The key idea is to take advantage of the optimality of the POD technique and its capability to extract the most energetic patterns of complex aerodynamic flow fields. First, the concept of Modal Assurance Criterion (MAC) is used to obtain a simple quantitative criterion to compare EFD measurements to CFD results. The comparison is based on the POD modes, extracted from each set of data. The analysis of the energy content of the modes allows to draw important conclusions about the role of the latter. The method is applied in the study of the flow field around a rectangular cylinder, which is either static or oscillating in a low-speed flow field. The second EFD/CFD integration technique deals with the reconstruction of a flow field from measured data, making use of CFD simulation results. The POD modes are first extracted from several CFD data sets, using a snapshot POD approach. Then the entire flow field of measured data can be reconstructed using a gappy POD method. The technique is applied to the transonic flow around a civil aircraft type wind tunnel model. The EFD measurements consist in pressure coefficient data from pressure ports or pressure-sensitive paint. It is shown that the complete flow field can be reconstructed from the pressure data with satisfactory accuracy and at relatively low computational cost. The work demonstrates the potential of the POD technique to integrate EFD and CFD data, leading to a combined, validated and complete analysis of the flow under consideration. [less ▲] Detailed reference viewed: 325 (42 ULg)Using Proper Orthogonal Decomposition Methods for Comparing CFD Results to Experimental Measurements Andrianne, Thomas ; Guissart, Amandine ; Terrapon, Vincent et al Scientific conference (2012, December 07) This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in ... [more ▼] This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in order to compare the unsteady aerodynamic flows around static and oscillating bodies obtained from wind tunnel testing and numerical simulations. Two dimensional Time-resolved Particle Image Velocimetry measurements are carried out on the upper surface a 4:1 rectangular cylinder. Simulations are performed using unsteady Reynolds-Averaged Navier-Stokes and an unsteady Discrete Vortex Method. It is demonstrated that the proposed technique is a good preliminary step for comparing the main characteristics of unsteady aerodynamic data. [less ▲] Detailed reference viewed: 67 (25 ULg)Using Proper Orthogonal Decomposition Methods for Comparing CFD Results to Experimental Measurements Andrianne, Thomas ; Guissart, Amandine ; Terrapon, Vincent et al in Proceedings of the 5th Symposium on Integrating CFD and Experiments in Aerodynamics (Integration 2012) (2012, October 03) This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in ... [more ▼] This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in order to compare the unsteady aerodynamic flows around static and oscillating bodies obtained from wind tunnel testing and numerical simulations. Two dimensional Time-resolved Particle Image Velocimetry measurements are carried out on the upper surface a 4:1 rectangular cylinder. Simulations are performed using unsteady Reynolds-Averaged Navier-Stokes and an unsteady Discrete Vortex Method. It is demonstrated that the proposed technique is a good preliminary step for comparing the main characteristics of unsteady aerodynamic data. [less ▲] Detailed reference viewed: 258 (47 ULg)Damping identification of linear dynamic systems using Common-base Proper Orthogonal Decomposition Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of ISMA2012 (2012, September 19) This paper presents a novel identification technique of the modal damping of linear systems. It is based on the Proper Orthogonal Decomposition (POD) of the free response of the system and extended to the ... [more ▼] This paper presents a novel identification technique of the modal damping of linear systems. It is based on the Proper Orthogonal Decomposition (POD) of the free response of the system and extended to the Common-base POD (CPOD) approach. Different initial conditions are applied to the system and the corresponding free responses are considered simultaneously. The CPOD technique 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, based on one set of initial conditions only. The ability of the technique to estimate the modal damping is demonstrated on a simulated mass-spring-damper system and an experimental system. Good agreement is shown between the damping estimates of the CPOD technique and the ones of the LSCF technique. The advantage and limitations of the present technique are discussed. [less ▲] Detailed reference viewed: 55 (3 ULg)Comparison of numerical results to experimental measurements using Proper Orthogonal Decomposition Andrianne, Thomas ; Dimitriadis, Grigorios Scientific conference (2012, May 24) Detailed reference viewed: 31 (6 ULg)Numerical simulations of torsional flutter oscillations of a bluff body: Energy issues, GraSMech poster session Andrianne, Thomas ; Dimitriadis, Grigorios Poster (2012, May) The possibility of harvesting energy from aeroelastic phenomena is assessed through numerical simulations. The unsteady aerodynamics around an aeroelastic structure are modeled using the Discrete Vortex ... [more ▼] The possibility of harvesting energy from aeroelastic phenomena is assessed through numerical simulations. The unsteady aerodynamics around an aeroelastic structure are modeled using the Discrete Vortex Method (DVM). The Torsional Flutter oscillations of a rectangular cylinder are studied in this work. The phenomenon is characterized by Limit Cycle Oscillations (LCOs) around the pitch axis of the rectangle. The complete bifurcation behaviour is investigated numerically and compared to wind tunnel measurements for validation. The energy issues are investigated in terms of the sensibility of the energy output to variations in the structural damping. [less ▲] Detailed reference viewed: 77 (16 ULg)Experiments on a pitch-plunge wing undergoing limit cycle oscillation Norizham, Abdul Razak ; Rothkegel Ide, José Ignacio ; Dimitriadis, Grigorios 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 ▲] Detailed reference viewed: 130 (11 ULg)A Cross-Validation Approach to Approximate Basis Function Selection of the Stall Flutter Response of a Rectangular Wing in a Wind Tunnel ; ; Andrianne, Thomas 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 ▲] Detailed reference viewed: 77 (12 ULg)Initial Investigation of Chordwise Flexible Flat Aerofoil ; ; et al in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 25) The size of small Unmanned Air Vehicles (UAVs) makes them susceptible to gusts, hence an evaluation of their aeroelastic performance is a necessary requirement. With advances in materials, new aircraft ... [more ▼] The size of small Unmanned Air Vehicles (UAVs) makes them susceptible to gusts, hence an evaluation of their aeroelastic performance is a necessary requirement. With advances in materials, new aircraft are ever lighter and more flexible, both in the span-wise and chord-wise direction. An experiment is set up to evaluate the aeroelastic performance of a 2D chord-wise aerofoil structure under gust loading, where the wing of a small Unmanned Air Vehicle (UAV) is considered by coupling a Finite Element (FE) structural model with a Doublet-Lattice Method (DLM) aerodynamic model; a new semi-analytical modelling approach is also described. The flexible aerofoil structure is then optimised by means of a genetic algorithm (GA) framework for the minimum weight, subject to aeroelastic constraints of flutter, divergence and structural displacement. [less ▲] Detailed reference viewed: 53 (2 ULg)Computational Considerations for the Prediction of Stall Flutter Watrin, Damien ; Dimitriadis, Grigorios ; et al 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 demonstrated that while current computational methods are able to predict the self-sustained oscillations characterizing a pitch-dominated stall flutter, including energy transfer, improvements are needed. The influence of grid, temporal integration, turbulence modeling, and flow equations is examined for the stall flutter starting solution of dynamic stall. [less ▲] Detailed reference viewed: 58 (17 ULg)Discrete Vortex Simulations of the torsional flutter oscillations of a 4:1 rectangular cylinder Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 24) This work presents aeroelastic simulations of a 2D bluff-body around its pitching degree of freedom. The numerical tool consists in an aerodynamic solver based on the Discrete Vortex Method (DVM), coupled ... [more ▼] This work presents aeroelastic simulations of a 2D bluff-body around its pitching degree of freedom. The numerical tool consists in an aerodynamic solver based on the Discrete Vortex Method (DVM), coupled with a linear structural model. The shape of the bluff-body is a sharp edged rectangular cylinder with a side ratio equal to 4. The numerical results are compared to the experimental measurements recently obtained by the authors.8 The validation is carried out in three steps: first the frequency content of the flow-field in the wake of the static body is investigated. Then the simulated unsteady flow-field around the imposed pitching motion of the body is compared to experimental flow visualizations. This comparison is performed using Proper Orthogonal Decomposition (POD). Finally, the simulation of the global aeroelastic behaviour, based on the coupling of the DVM code to the structural model of the pitching degree of freedom is carried out and the results are compared to measured aeroelastic responses.. Very good agreements are found between numerical and experimental results, demonstrating the capabilities of the numerical tool to simulate complex unsteady aerodynamics around an oscillating bluff-body. [less ▲] Detailed reference viewed: 43 (13 ULg)Computational Identification of Non-Linear Damping in an Aeroelastic System ; Dimitriadis, Grigorios in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 23) 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: 22 (1 ULg) |
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