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Approach to Induced Drag Reduction with Experimental Evaluation
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.ORCID iD: 0000-0002-3199-8534
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2005 (English)In: Journal of Aircraft, ISSN 0021-8669, Vol. 42, no 6, 1478-1485 p.Article in journal (Refereed) Published
Abstract [en]

An approach to minimize the induced drag of an aeroelastic configuration by means of multiple leading- and trailing-edge control surfaces is investigated. A computational model based on a boundary-element method is constructed and drag-reducing flap settings are found by means of numerical optimization. Further, experiments with an elastic wind-tunnel model are performed in order to evaluate the numerically obtained results. Induced-drag results are obtained by analyzing lift distributions computed from optically measured local angles of attack because standard techniques proved insufficient. Results show that significant reductions of induced drag of flexible wings can be achieved by using optimal control surface settings.

Place, publisher, year, edition, pages
2005. Vol. 42, no 6, 1478-1485 p.
Keyword [en]
Aeroelastic configuration; Drag reduction; Flap settings; Lift distributions
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-7268DOI: 10.2514/1.11713ISI: 000233846200012Scopus ID: 2-s2.0-29544442463OAI: oai:DiVA.org:kth-7268DiVA: diva2:12227
Note
QC 20100531. Konferens: AIAA/ASME/ASCE/AHS/ASC 45th Structures, Structural Dynamics and Materials Conference Palm Springs, CA, APR 19-22, 2004Available from: 2007-06-01 Created: 2007-06-01 Last updated: 2011-12-08Bibliographically approved
In thesis
1. Aeroelastic Concepts for Flexible Aircraft Structures
Open this publication in new window or tab >>Aeroelastic Concepts for Flexible Aircraft Structures
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis, aeroelastic concepts for increased aircraft performance are developed and evaluated. Active aeroelastic concepts are in focus as well as robust analysis concepts aiming at efficient analysis using numerical models with uncertain or varying model parameters.

The thesis presents different approaches for exploitation of fluid-structure interaction of active aeroelastic structures. First, a high aspect ratio wing in wind tunnel testing conditions is considered. The wing was developed within the European research project \textit{Active Aeroelastic Aircraft Structures} and used to demonstrate how structural flexibility can be exploited by using multiple control surfaces such that the deformed wing shape gives minimum drag for different flight conditions. Two different drag minimization studies are presented, one aiming at reduced induced drag based on numerical optimization techniques, another one aiming at reduced measured total drag using real-time optimization in the wind tunnel experiment. The same wing is also used for demonstration of an active concept for gust load alleviation using a piezoelectric tab. In all studies on the high aspect ratio wing, it is demonstrated that structural flexibility can be exploited to increase aircraft performance.

Other studies in this thesis investigate the applicability of robust control tools for flutter analysis considering model uncertainty and variation. First, different techniques for taking large structural variations into account are evaluated. Next, a high-fidelity numerical model of an aircraft with a variable amount of fuel is considered, and robust analysis is applied to find the worst-case fuel configuration. Finally, a study investigating the influence of uncertain external stores aerodynamics is presented. Overall, the robust approach is shown to be capable of treating large structural variations as well as modeling uncertainties to compute worst-case configurations and flutter boundaries.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 31, 24, 16, 16, 16, 23 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2007:29
Keyword
aeroelasticity, active aeroelastic aircraft structures, aeroelastic control, wind-tunnel testing, flutter analysis, robust flutter analysis, worst-case configuration
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-4419 (URN)978-91-7178-706-4 (ISBN)
Public defence
2007-06-15, F3, Lindstedtsvägen 26, Stockholm, 13:15
Opponent
Supervisors
Note
QC 20100713Available from: 2007-06-01 Created: 2007-06-01 Last updated: 2010-07-13Bibliographically approved
2. Aeroelastic Concepts for Flexible Wing Structures
Open this publication in new window or tab >>Aeroelastic Concepts for Flexible Wing Structures
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis summarizes investigations performed within design, analysis and experimental evaluation of flexible aircraft structures. Not only the problems, but rather the opportunities related to aeroelasticity are discussed.

In the first part of the thesis, different concepts for using active aeroelastic configurations to increase aircraft performance are considered. In particular, one study deals with the minimization of the induced drag of a highly flexible wing by using multiple control surfaces. Another study deals with a possible implementation of a high-bandwidth piezo electric actuator for control applications using aeroelastic amplification.

The second part of the thesis deals with the development of an approach for modeling and analysis of flexible structures considering uncertainties in analysis models. Especially in cases of large structural variations, such as fuel level variations, a fixed-base modal formulation in robust flutter analysis may lead to incorrect results. Besides a discussion about this issue, possible means of treating this problem are presented.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 25 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2005:22
Keyword
active aeroelasticity, flexible wings, aeroelastic control, design, experiments, testing, analysis, robust, uncertainty
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-244 (URN)
Presentation
2005-06-10, S40, Teknikringen 8, 10:00
Opponent
Supervisors
Note
QC 20101130Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2010-12-06Bibliographically approved
3. On an Efficient Method fo Time-Domain Computational Aeroelasticity
Open this publication in new window or tab >>On an Efficient Method fo Time-Domain Computational Aeroelasticity
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The present thesis summarizes work on developing a method for unsteady aerodynamic analysis primarily for aeroelastic simulations. In contrast to widely used prediction tools based on frequency-domain representations, the current approach aims to provide a time-domain simulation capability which can be readily integrated with possibly nonlinear structural and control system models. Further, due to the potential flow model underlying the computational method, and the solution algorithm based on an efficient boundary element formulation, the computational effort for the solution is moderate, allowing time-dependent simulations of complex configurations. The computational method is applied to simulate a number of wind-tunnel experiments involving highly flexible models. Two of the experiments are utilized to verify the method and to ascertain the validity of the unsteady flow model. In the third study, simulations are used for the numerical optimization of a configuration with multiple control surfaces. Here, the flexibility of the model is exploited in order to achieve a reduction of induced drag. Comparison with experimental results shows that the numerical method attains adequate accuracy within the inherent limits of the potential flow model. Finally, rather extensive aeroelastic simulations are performed for the ASK 21 sailplane. Time-domain simulations of a pull-up maneuver and comparisons with flight test data demonstrate that, considering modeling and computational effort, excellent agreement is obtained. Furthermore, a flutter analysis is performed for the same aircraft using identified frequency-domain loads. Results are found to deviate only slightly from critical speed and frequency obtained using an industry-standard aeroelastic analysis code. Nevertheless, erratic results for control surface hinge moments indicate that the accuracy of the present method would benefit from improved control surface modeling and coupled boundary layer analysis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005
Series
Trita-AVE, ISSN 1651-7660 ; 2006:1
Keyword
aeroelasticity, unsteady aerodynamics, boundary element method, multidisciplinary simulation
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-584 (URN)91-7178-243-5 (ISBN)
Public defence
2006-01-24, Kollegiesalen F3, F, Lindstedtsvägen 26, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100531Available from: 2006-01-16 Created: 2006-01-16 Last updated: 2011-12-08Bibliographically approved

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