Srinivas Vasista

Compliant structures-based wing and wingtip morphing devices

Purpose The purpose of this paper is to provide an overview of the design and experimental work of compliant wing and wingtip morphing devices conducted within the EU FP7 project NOVEMOR and to demonstrate that the optimization tools developed can be used to synthesize compliant morphing devices. Design/methodology/approach The compliant morphing devices were “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, aerodynamic shape optimization able to take into account the structural behaviour of the morphing skin, continuum-based and load path representation topology optimization methods and multi-objective optimization coupled with genetic algorithm for compliant internal substructure design. Low-speed subsonic wind tunnel testing was performed as an effective means of demonstrating proof-of-concept. Findings It was found that the optimization tools could be successfully implemented in the manufacture and testing stage. Preliminary insight into the performance of the compliant structure has been made during the first wind tunnel tests. Practical implications The tools in this work further the development of morphing structures, which when implemented in aircraft have potential implications to environmentally friendlier aircrafts. Originality/value The key innovations in this paper include the development of a composite skin optimization tool for the design of highly 3D morphing wings and its ensuing manufacture process; the development of a continuum-based topology optimization tool for shape control design of compliant mechanisms considering the stiffness and displacement functions; the use of a superelastic material for the compliant mechanism; and wind tunnel validation of morphing wing devices based on compliant structure technology.

Design and Testing of a Compliant Mechanism-Based Demonstrator for a Droop-Nose Morphing Device

A demonstrator morphing leading edge was designed and manufactured as an intermediary step in preparation for wind tunnel testing of a droop-nose adaptive morphing wingtip (AMWT) as part of the European FP7 project NOVEMOR. This demonstrator features a flexible fiberglass skin and a monolithic aluminum internal compliant mechanism and support structure for lightweight design. The design process involves the design of the skin via a structural optimization tool, followed by continuum gradient-based topology optimization of first the compliant mechanism and then the support structure. The skin was manufactured using prepreg Hexcel HexPly® 913 plies, the aluminum internal structure was laser cut from stock plate material and the compliant region was driven by a linear stepper motor actuator. Displacements and strains were measured and compared with target values and that of finite element computations and overall show good agreement; however issues such as grey-areas and hinge-regions in the topology optimization need to be addressed for the final wind tunnel design for better post-processing and reduced stress concentrations.

Progress in Efficient Active High-Lift

This paper presents some of the progress in research on efficient high-lift systems for future civil aircraft achieved by the Coordinated Research Centre CRC 880 sponsored by the German Research Foundation. Several new approaches to increasing the lift are applied as part of the design of a reference aircraft with short take-off and landing capability: The numerically predicted positive effect of Coanda jet blowing at the trailing edge flap is validated in water tunnel experiments. Robust miniature pressure and hot-fi�lm sensors are developed for the closed-loop control of a piezo-actuated blowing lip. A flexible leading-edge device utilizes composite materials, for which new structural designs are developed. Additionally, a potential de-icing system, as well as a lightning-strike protection are presented. A high power-density electrically driven compressor with a broad operating range is designed to provide the blowing air ow. Different propulsion systems for the reference aircraft are evaluated. An ultra-high bypass ratio engine is considered to be most promising, and thus a preliminary fan stage design process is established. The rotor dynamic influences of the engine on the aircraft structure are investigated through a hybrid approach using a multibody model and modal reduction.

BENCH TOP TEST OF A DROOP NOSE WITH COMPLIANT MECHANISM

Morphing is a technology with high potential to reduce emissions in aviation, since it enables wings to adapt their shape to operate at a higher efficiency over the full range of flight conditions. This paper is presenting a concept to adapt camber by drooping the nose. The scope is the setup and bench top testing of a full scale wing tip leading edge wind tunnel model with a morphing droop nose. The complete model features a span of 1.3 m and a strong taper from the root to the tip. For completeness, the design approach is covered as well. The design comprises a GFRP skin to be drooped by two compliant mechanisms, which are driven by linear motors. The compliant morphing devices are “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, continuum-based and load path representation topology optimization methods for compliant internal substructure design. The compliant mechanism is manufactured by nickel-titanium alloy to allow high strains in the order of several percent, which is shown to be critical in the design of such compliant mechanisms. In order to validate the models, strains within the mechanisms are measured while drooping the nose in the bench top test. This is done after installing the mechanisms into the leading edge skin. It can be shown, that the simulation for the inboard mechanism is close to the experimental results. The comparison of strain levels in the skin and in the mechanism during droop reveals that the stiffness distribution between these two components is quite different. As a result this ratio can be taken into account in future design processes in order to distribute strains more evenly. Moreover the 3D shapes of the morphed and clean skin are measured and their comparison with the target shapes is presented as well. Finally, the bench top tests are a proof of concept for the overall concept and design which resultes in a “go” for the following low speed subsonic wind tunnel tests.Copyright

Three-dimensional design of a large-displacement morphing wing droop nose device:

The numerical three-dimensional structural design of a large-displacement flexible morphing wing leading edge, otherwise known as a droop nose, is presented in this article. The droop nose is an essential component of a novel internally blown high-lift system for a transport aircraft to delay stall and reduce internal compressor requirements. A design chain consisting of optimization procedures was used to arrive at the structural design of the droop nose composed of a composite fiberglass skin with integral stringers and supporting kinematic mechanisms. The optimization tools aim to produce a design with minimal error to the critical target shapes. A maximum final error of 10.09 mm between calculated and target trajectories of the stringers was found after the kinematic optimization stage. After inputting the kinematic optimization results into the skin optimization stage and solving, a maximum error in the order of 13 mm and curvature difference 0.0028 1/mm were calculated, occurring in the outboard region. Prior two-dimensional analyses with similar shape deviations showed 0.4% lift reduction though further three-dimensional investigations are required. Concepts for integrating industrial requirements abrasion and lightning strike protection and in-flight de-icing into a multifunctional skin show promise and the resulting aerodynamic surface quality was found to be adequate.

Active and Passive Smart Structures and Integrated Systems 2016

This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.

Lessons learned from wind tunnel testing of a droop-nose morphing wingtip

This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.