R. De Breuker

Static/Dynamic Edge Movability Effect on Non-Linear Aerothermoelastic Behavior of Geometrically Imperfect Curved Skin Panel: Flutter and Post-Flutter Analysis

This paper addresses the problem of the aerothermoelastic modeling behavior and analyses of skin curved panels with static and dynamic edge movability effect in high supersonic flow. Flutter and post-flutter behavior will be analyzed toward determining under which conditions such panels will exhibit a benign instability, that is a stable limit cycle oscillation, or a catastrophic instability, that is an unstable LCO. The aerothermoelastic governing equations are developed from the geometrically non-linear theory of infinitely long two dimensional curved panels. Von Karman non-linear strain-displacement relation in conjunction with the Kirchhoff plate-hypothesis is adopted. A geometrically imperfect curved panel forced by a supersonic/hypersonic unsteady flow is numerically investigated using Galerkin approach. These equations are based on the third-order piston theory aerodynamic for modeling the flow-induced forces. Furthermore, the effects of thermal degradation and Kelvins model of structural damping independent of time and temperature are also considered in this model. Computational analysis and discussion of the finding along with pertinent conclusions are presented.

Effect of span-morphing on the longitudinal flight stability and control

Morphing wing strategies can be applied to configure aircraft geometry to successfully complete a mission/s. This requires fulfillment of requirements set within a series of flight phases, which generally specify an objective to be completed and constraints to be satisfied whilst optimising some measure of performance or efficiency. The following paper presents results from a software framework to assess the potential benefits of span morphing in performance and efficiency. An investigation of the effect of morphing on flight stability and control is presented. As an example, span variation from a nominal aspect ratio of 6.67 for a Unmanned Air Vehicle (UAV) of 25kg is presented, with results given for a representative mission profile for typical operations. A structural concept that integrates span retraction is assumed.

Active aeroelastic control aspects of an aircraft wing by using synthetic jet actuators : Modeling, simulations, experiments

This paper discusses modeling, simulations and experimental aspects of active aeroelastic control on aircraft wings by using Synthetic Jet Actuators (SJAs). SJAs, a particular class of zero-net mass-flux actuators, have shown very promising results in numerous aeronautical applications, such as boundary layer control and delay of flow separation. A less recognized effect resulting from the SJAs is a momentum exchange that occurs with the flow, leading to a rearrangement of the streamlines around the airfoil modifying the aerodynamic loads. Discussions pertinent to the use of SJAs for flow and aeroelastic control and how these devices can be exploited for flutter suppression and for aerodynamic performances improvement are presented and conclusions are outlined.

Active Flow and Aeroelastic Control of Lifting Surfaces Using Synthetic Jet Actuators

Active flow control devices such as zero-net-mass-flux actuators have broad aeronautical applications. Among them, low power and lightweight Synthetic Jet Actuators (SJAs) can be used to improve the performance of flight vehicles, expand their flight envelope and prevent catastrophic failure by flutter instability. Numerical and experimental investigations are proving that SJAs are effective in actively altering the boundary layer and influencing the flow separation. Furthermore, the effect of the momentum exchange due to the SJAs leads to a rearrangement of streamlines around the wing, thus modifying the unsteady aerodynamics forces. Incompressible Reynolds-Averaged Navier-Stokes (RANS) computations are performed with FLUENT to estimate the efficiency of the SJAs in modifying pressure distribution, and consequently the aerodynamic forces on the lifting surface to which they are hosted. Simulations accounts for the SJA diameter, location, oscillation frequency and its strength. The computational simulations show that SJAs produce sufficiently large aerodynamic forces to expand the flutter boundary and to counteract self sustained limit cycle oscillations (LCOs), e.g. non-linear aeroelastic vibrations, due to the inherent structural and aerodynamic nonlinearities present in the wing structure and flow field respectively. Although LCOs do not produce immediate failure of the wing, the self sustained vibrations can lead to premature failure due to fatigue and for this reason a carefully designed LCO suppression mechanism is of interest to the aeronautical community. Two phases of experimental tests are under investigation. First, a two degree-of-freedom plunging and pitching wing apparatus, representing a wing structure with elasticity concentrated in elastic springs has been designed and characterized. Stiffness and damping characteristics have been estimated along with the flutter and LCO analysis. Once the apparatus characterization is complete, accurate analytical models can be proposed and used to help the development of active flow control systems and their associated control laws. Second, active flow control devices (SJAs) will be installed on a wing section and a proper feedback control law will be implemented to demonstrate the suppression of LCOs. The final paper will present experimental and numerical results showing the effectiveness for suppressing aeroelastic vibrations. The combination of experimental and numerical simulations will provide the aerospace industry with design guidance for flow and aeroelastic control devices, insight into flow phenomena, and feasibility analysis of SJAs for specific applications.

The Effects of Aeroelastic Tailoring on Flight Dynamic Stability

This paper presents a unified framework for aeroelastic tailoring of free-flying aircraft with composite wings. A continuous-time state-space model is used to describe the flow. The 3D composite wing structures is condensed into a Timoshenko beam model by means of a cross-sectional modeler. The aerodynamic and structural models are closely coupled with the six degrees of freedom flight dynamic equations of motion in the state-space formulation. This paper refers to the clamped-wing aeroelastic tailoring as classic aeroelastic tailoring. Hence, the term aeroelastic tailoring will point at the novel approach that includes free-flying aeroelastic phenomena into the optimization process. The emphasis of the present paper is to show the effects of aeroelastic tailoring on body-freedom flutter and flight dynamic stability at large. The results of this paper will be used in the further development of aeroelastic tailoring practices for composite aircraft design.

A Paradigm Shift in Teaching Aerospace Engineering: From Campus Learners to Professional Learners – a Case Study on Online Courses in Smart Structures and Air Safety Investigation

In this paper, the transition from teaching on-campus to an online audience consisting of working professionals in an Aerospace Engineering context is described. The differences in the learner’s needs and the transition in teaching methods and style that is required from teaching staff is discussed. This is illustrated by two case studies: for Smart Structures and for Air Safety Investigation. Recommendations on how universities can contribute to Life Long Learning are given.

Optimization of Linear Parameterizable ℋ∞ Controllers in the Frequency Domain

Abstract In this paper a novel approach for ℋ ∞ controller design for linear parameterizable controllers is presented. The approach uses the generalized Nyquist stability criterion to find the parameters of linear parameterized controllers for Multi-Input Multi-Output (MIMO) systems. The main advantage of the proposed approach is that the generalized plant does not have to be diagonally dominant and that there is no need for a desired open-loop response function. By constraining the Nyquist curve from certain parts in the frequency domain, controller parameters that guarantee stability and performance of the closed-loop system can be found. The method is successfully applied to two cases involving a double-mass-spring-damper system. In the first case only controller parameters are optimized and in the second case both structural and controller parameters are optimized.