Fernando Lau

Optimization of a Morphing Wing Based on Coupled Aerodynamic and Structural Constraints

This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicles performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

AERO-STRUCTURAL OPTIMIZATION AND PERFORMANCE EVALUATION OF A MORPHING WING WITH VARIABLE SPAN AND CAMBER

An aero-structural design and analysis study of a telescopic wing with a conformal camber morphing capability is presented. An aerodynamic analysis of a telescoping wing, first with a high speed airfoil followed by an analysis with a low speed airfoil is performed. The data obtained from these analyses is used to determine the optimum polar curves for drag reduction at different speeds. This information in turn provided the background for devising an optimal morphing strategy for drag reduction assuming that the telescoping wing airfoil has the capability to step morph between the high and low speed airfoils. Next, a conformal camber morphing concept is introduced. The concept is based on a non-uniform thickness distribution along the chord of a wing shell section that deforms from a symmetrical airfoil shape into a cambered airfoil shape under actuation. Structural optimization based on finite element models is used to obtain the shell thickness distribution for minimum shell section weight and best airfoil shape adjustment. Finally, a comparison study between the performance of an aircraft equipped with a morphing wing (telescopic wing combined with conformal camber morphing) and the performance of the same aircraft equipped with an optimized fixed wing for 30 m/s cruise speed and 100 N weight is presented. Aerodynamic optimization based on computational fluid dynamics models is used for the optimum fixed wing geometric parameters calculations. The optimal wing configurations for various performance parameters are calculated. The morphing wing generally outperforms the optimum fixed wing with the exception of a 10% reduction in rate of climb and 4% drag penalty at 30 m/s cruise speed.

On sound in an inverse sinusoidal nozzle with low Mach number mean flow

The quasi‐one‐dimensional propagation of sound, in a throated convergent–divergent nozzle, with entry and exit baffle at finite distance, containing a low Mach number mean flow, is studied in four steps. The low Mach number nozzle wave equation, is obtained, both for the acoustic potential and velocity, using two methods, viz. (a) elimination between the equations of motion and (b) an acoustic variational principle. For the case of inverse sinusoidal ducts, exact solutions are obtained, in terms of elementary functions, for the acoustic potential and velocity, in horns and nozzles. The reduced acoustic velocity, i.e., correction to ray approximation, is reconsidered as an exact, closed series solution, of a modified Mathieu equation, with imaginary coefficients. The plots of amplitude and phase versus distance, for various low Mach numbers, and increasing wave numbers show a number of effects, which may be interpreted as follows: (i) acoustic energy is focused in the converging duct, leading to a peak hal...

Multidisciplinary Design Optimization of a Morphing Wing for an Experimental UAV

§The aim of this work is to design a morphing wing concept for a small unmanned aerial vehicle (UAV), in order to improve the vehicle’s performance over its intended speed range. The wing is designed using a multidisciplinary design optimization framework where an aerodynamic shape optimization code coupled with a structural morphing model environment is setup to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as structural modelling. The aerodynamic shape optimization code, which uses an inviscid/viscous 2-dimensional panel method formulation coupled with a non-linear lifting-line algorithm and an sequential quadratic programming (SQP) optimization algorithm is suitable for preliminary wing design optimization tasks, although its robustness still needs further improvements. The morphing concept, based on changes in wing planform shape and wing section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between initial wing performance, optimal morphing wing performance and the performance of the wing obtained as the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the UAV when fitted with this new morphing wing are also included. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

On Sound Generation by Moving Surfaces and Convected Sources in a Flow

The theory of sound generation by surfaces in arbitrary motion is presented, with two generalizations relative to the Ffowcs-William Hawkins (FWH) equation: (i) it allows for the presence of a steady, non-uniform potential flow of low Mach number; (ii) it includes the effects on the radiation field of reflections from solid surfaces, e.g. these which cause non-uniformity of the flow. The final result is a generalization of the Kirchhoff integral with: (i) a retarded time modified by sound convection by the mean flow; (ii) position coordinates of observer and source modified to account for the presence of the obstacles which reflect sound waves and cause the mean flow to be non-uniform. An alternative generalization of the Kirchhoff integral is presented for sources in arbitrary motion in an uniform mean flow with unrestricted Mach number. The two generalized forms of the Kirchhoff integral also apply to convected sources of sound, such as the turbulence noise associated with vorticity and the entropy noise due to convected fluid inhomegeneities. The two noise sources are shown to be dominant at low Mach number, relative to other noise sources present in an inhomogeneous potential flow with unrestricted Mach number. In the latter case applies the (i) inhomogeneous high-speed wave equation, that includes as particular cases the (ii) convected and (iii) classical wave equations. The latter two (ii–iii) are obtained from (α) the Laplace equation using the retarded time. All three (i–iii) are obtained by two more distinct methods: (β) elimination among the equations of fluid mechanics for the stagnation enthalpy as acoustic variable; (γ) an acoustic variational principle for the acoustic potential in a steady homentropic non-homogeneous potential mean flow with unrestricted Mach number.

On the effect of wall undulations on the acoustics of ducts with flow

The acoustic wave equation for quasi-one-dimensional propagation is obtained, along a duct with a small wall sinusoidal perturbation and containing a low Mach number mean flow. The motivation is the study of the effect of wall roughness on the propagation of sound in a duct, and also of the effect of repeated reflections at periodic changes in cross-sectional area. The ray approximation, which holds only for wavelengths which are short compared with the length scales of the variation of the cross-section and mean flow velocity, is used as a factor to reduce the wave equation to a Schrodinger form. The exact solutions are obtained, without restriction, as power series expansions around the middle of the duct; since this solution fails to converge at the two ends of the duct it is matched to the other solutions there. In this way it is possible to calculate everywhere reduced potential, (unreduced) potential, velocity and pressure perturbations. These are plotted as a function of the longitudinal co-ordinates along the duct for several values of the three dimensionless parameters in the problem, viz., (1) the relative height of wall corrugations, (2) the Mach number of the mean flow at the central section and (3) the wavenumber made dimensionless multiplying by the periodicity of corrugations.

Flow-Induced Noise and Vibration in Aircraft Cylindrical Cabins: Closed-Form Analytical Model Validation

The turbulent boundary layer is a major source of interior noise in transport vehicles, mainly in aircraft during cruise flight. Furthermore, as new and quieter jet engines are being developed, the turbulent flow-induced noise will become an even more important topic for investigation. However, in order to design and develop systems to reduce the cabin interior noise, the understanding of the physical system dynamics is fundamental. In this context, the main objective of the current research is to develop closed-form analytical models for the prediction of turbulent boundary-layer-induced noise in the interior of aircraft cylindrical cabins. The mathematical model represents the structural-acoustic coupled system, consisted by the aircraft cabin section coupled with the fuselage structure. The aircraft cabin section is modeled as a cylindrical acoustic enclosure, filled with air. The fuselage structure, excited by external random excitation or by turbulent flow, is represented through two different models: (1) as a whole circular cylindrical shell with simply supported end caps and (2) as a set of individual simply supported open circular cylindrical shells. This paper presents the results obtained from the developed analytical framework and its validation through the successful comparison with several experimental studies. Analytical predictions are obtained for the shell structural vibration and sound pressure levels, for the frequency range up to 10,000 Hz.

SMorph - Smart Aircraft Morphing Technologies Project

SMorph (Smart Aircraft Morphing Technologies) is a Eurocores S3T collaborative research project involving three university partners from the UK, Portugal and Italy. The aim of the project is to develop novel structural concepts and implementations of morphing aeroelastic structures. An overview of the current status of the project is provided, including description of the development, modelling and design optimization of several morphing aeroelastic structures. Reference will also be made to the design, manufacture and testing of wind tunnel and RPV demonstrator models.

Multidisciplinary Performance Based Optimization of Morphing Aircraft

Nowadays the aeronautic industry is battling with contradictory requirements. In one hand, there is the need to increase speed and capacity, while, on the other hand, there is an increasing need to minimize the environmental impact caused by air travel. The permanent need to improve aircraft performance and efficiency, have impelled not only the use of new aircraft configuration, but also the introduction of morphing solutions on the existing configurations. In order to achieve the optimal aircraft configuration or the best morphing solution for a determined mission, it is necessary to explore Multidisciplinary Design Optimization (MDO) solutions in the research and development process. A MDO framework is being developed for preliminary design and analysis of novel conjurations, including the capability to analyze morphing solutions. This tool was developed to be both modular and versatile, allowing the user to create custom plug-in like modules to tailor the software to each users needs. In this framework, the main aircraft disciplines are integrated with optimization software in a single optimization statement. With computational efficiency in mind, surrogate models of the disciplines are built and the quality of these approximation models is verified. Disciplines can be replaced by corresponding existing or pre-calculated databases. This work is being developed within the EU 7th Framework Project NOVEMOR, which has two main objectives: novel configurations and morphing solutions assessment. Firstly, for a conventional regional jet it is assessed the benefits of introducing a morphing wingtip for three different flight conditions. Secondly, morphing bending and twist controls were applied to a reference joined-wing configuration to improve lateral-directional stability.

Prediction of turbulent boundary layer induced noise in the cabin of a BWB aircraft

This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). While, in previous works, the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is analyzed. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabin of a Blended Wing Body (BWB) aircraft, for the frequency range 0-1000 Hz. The results show that the number of vibrating panels significantly affects the interior noise levels. Itis shown that the average SPL,over the cabin volume, increases with the number of vibrating panels. Additionally, the model is able to predict local SPL values, at specific locations in the cabin, which are also affected with by number of vibrating panels, and are different from the average values.