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CONTENTS
Volume 4, Number 2, March 2017
 

Abstract
Aeroelastic performance controls wing shape in flight and its behaviour under manoeuvre and gust loads. Controlling the wing\'s aeroelastic performance can therefore offer weight and fuel savings. In this paper, the rib orientation and the crenellated skin concept are used to control wing deformation under aerodynamic load. The impact of varying the rib/crenellation orientation, the crenellation width and thickness on the tip twist, tip displacement, natural frequencies, flutter speed and gust response are investigated. Various wind-off and wind-on loads are considered through Finite Element modelling and experiments, using wings manufactured through polyamide laser sintering. It is shown that it is possible to influence the aeroelastic behaviour using the rib and crenellation orientation, e.g., flutter speed increased by up to 14.2% and gust loads alleviated by up to 6.4%. A reasonable comparison between numerical and experimental results was found.

Key Words
aeroelastic tailoring; aeroelasticity; structural dynamics

Address
Guillaume Francois, Jonathan E. Cooper and Paul M. Weaver : Department of Aerospace Engineering, University of Bristol, BS8 1TR, U.K.

Abstract
This paper summarises the design of a gust generator and the comparison between high fidelity numerical results and experimental results. The gust generator has been designed for a low subsonic wind tunnel in order to perform gust response experiments on wings and assess load alleviation. Special attention has been given to the different design parameters that influence the shape of the gust velocity profile by means of CFD simulations. Design parameters include frequency of actuation, flow speed, maximum deflection, chord length and gust vane spacing. The numerical results are compared to experimental results obtained using a hot-wire anemometer and flow visualisation by means of a tuft and smoke. The first assessment of the performance of the gust generator showed proper operation of the gust generator across the entire range of interest.

Key Words
gust generator; computational fluid dynamics; fluid structure interaction; experimental aerodynamics; experimental aeroelasticity

Address
Paul M.G.J. Lancelot, Jurij Sodja, Noud P.M. Werter and Roeland De Breuker : Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands

Abstract
The presented paper gives an overview of several projects addressing the experimental characterization and control of the buffet phenomenon on 3D turbulent wings in transonic flow conditions. This aerodynamic instability induces strong wall pressure fluctuations and therefore limits flight domain. Consequently, to enlarge the latter but also to provide more flexibility during the design phase, it is interesting to try to delay the buffet onset. This paper summarizes the main investigations leading to the achievement of open and closed-loop buffet control and its experimental demonstration. Several wind tunnel tests campaigns, performed on a 3D half wing/fuselage body, enabled to characterize the buffet aerodynamic instability and to study the efficiency of innovative fluidic control devices designed and manufactured by ONERA. The analysis of the open-loop databases demonstrated the effects on the usual buffet characteristics, especially on the shock location and the separation areas on the wing suction side. Using these results, a closed-loop control methodology based on a quasi-steady approach was defined and several architectures were tested for various parameters such as the input signal, the objective function, the tuning of the feedback gain. All closed-loop methods were implemented on a dSPACE device able to estimate in real time the fluidic actuators command calculated mainly from the unsteady pressure sensors data. The efficiency of delaying the buffet onset or limiting its effects was demonstrated using the quasi-steady closedloop approach and tested in both research and industrial wind tunnel environments.

Key Words
transonic flow; buffet control; fluidic device; open-loop; closed-loop

Address
Arnaud Lepage, Arnaud Geeraert :ONERA, Aeroelasticity and Structural Dynamics Department, Châtillon, 92320, France
Julien Dandois : ONERA, Applied Aerodynamics Department, Meudon, 92190, France
Pascal Molton : Fundamental and Experimental Aerodynamics Department, Meudon, 92190, France
Frédéric Ternoy : Model Design and Manufacturing Department, Lille, 59000, France
Jean Bernard Dor, Eric Coustols : Aerodynamics and Energetics Modelling Department, Toulouse, 31000, France

Abstract
The optimum design of structures with frequency constraints is of great importance in the aeronautical industry. In order to avoid severe vibration, it is necessary to shift the fundamental frequency of the structure away from the frequency range of the dynamic loading. This paper develops a novel topology optimisation method for optimising the fundamental frequencies of structures. The finite element dynamic eigenvalue problem is solved to derive the sensitivity function used for the optimisation criteria. An alternative material interpolation scheme is developed and applied to the optimisation problem. A novel level-set criteria and updating routine for the weighting factors is presented to determine the optimal topology. The optimisation algorithm is applied to a simple two-dimensional plane stress plate to verify the method. Optimisation for maximising a chosen frequency and maximising the gap between two frequencies are presented. This has the application of stiffness maximisation and flutter suppression. The results of the optimisation algorithm are compared with the state of the art in frequency topology optimisation. Test cases have shown that the algorithm produces similar topologies to the state of the art, verifying that the novel technique is suitable for frequency optimisation.

Key Words
optimisation; topology; flutter; natural frequency; level-set

Address
David J. Munk, Gareth A. Vio and Grant P. Steven : AMME, The University of Sydney, Bld J11, Sydney, NSW, 2006, Australia

Abstract
In a flexible airvehicle, an assessment of the structural coupling levels through analysis and experiments provides structural data for the design of notch filters which are generally utilized in the flight control system to attenuate the flexible response pickup. This is necessitated as during flight, closed loop control actuation driven with flexible response inputs could lead to stability and performance related problems. In the present work, critical parameters influencing servoelastic response have been identified. A sensitivity study has been carried out to assess the extent of influence of each parameter. A multi-parameter tuning approach has been implemented to achieve an enhanced analytical model for improved predictions of aircraft servoelastic response. To illustrate the model updation approach, initial and improved test analysis correlation of lateral servoelastic responses for a generic flexible airvehicle are presented.

Key Words
servoelastic response; lateral dynamics; sensitivity study; multi-parameter updation

Address
Prabha Srinivasan : Aeronautical Development Agency, PB 1718, Vimanapura Post, Bengaluru 560017, India
Ashok Joshi : Department of Aerospace Engineering, Indian Institute of Technology, Powai, Mumbai 400076, India

Abstract
This paper focuses on the computational study of nonlinear effects of unsteady aerodynamics for non-classical aileron buzz. It aims at a comprehensive investigation of the aileron buzz phenomenon under varying flow parameters using the describing function technique with multiple inputs. The limit cycle oscillatory behavior of an asymmetrical airfoil is studied initially using a CFD-based numerical model and direct time marching. Sharp increases in limit cycle amplitude for varying Mach numbers and angles of attack are investigated. An aerodynamic describing function is developed in order to estimate the variation of limit cycle amplitude and frequency with Mach number and angle of attack directly, without time marching. The describing function results are compared to the amplitudes and frequencies predicted by the CFD calculations for validation purposes. Furthermore, a limited sensitivity analysis is presented to demonstrate the potential of the approach for aeroelastic design.

Key Words
computational aeroelasticity; describing function; aileron buzz; fluid structure interaction; limit cycle oscillation

Address
Muhammad I. Zafar, Francesca Fusi and Giuseppe Quaranta : Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, Campus Bovisa Sud, via La Masa, 34, 20165 – Milano, Italy


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