Design and Experimental Characterization of an Actuation System for Flow Control of an Internally Blown Coanda Flap

The focus of the work is on the evaluation, development and integration of a robust actuator system for three-dimensional flow control of a blown Coanda flap to improve the high lift system of commercial aircraft. As part of the research work presented, the system is integrated into a wind tunnel model in order to influence the flow across the entire width of the model. The system developed is based on individual bending transducers that can vary the height of the blowing slot dynamically. The system is divided into 33 segments and is therefore able to implement static and dynamic actuation along the wing-span (3D-actuation). All segments can be controlled independently and thus offer great optimization potential for an effective flow control. Different configurations were developed and evaluated against each other with respect to the demanding requirements (small installation space, frequency range from 5 Hz to 300 Hz, 1 bar pressure, 0.4 mm deflection, 1 m span). The design of the blown flap has been specified in an iterative design process. In the final configuration, all mechanical components are reduced to the bare minimum for weight reduction reasons, in order to meet the dynamic requirements of the wind tunnel model. To characterize the lip segments, a test device has been designed that can be pressurized to generate aerodynamic loads on the lip segments. Finally, 33 lip segments were integrated into a wind tunnel model and tested intensively as part of a measurement campaign. The first aerodynamic results show an increase in lift of up to ∆Ca = 0.57. These aerodynamic gains are achieved at amplitudes that do not require the lip segments to completely close or open the blowing slot, which shows the advantage of the current lip design that enables activation with independently controlled stationary and unsteady components

Automated Scarfing Process for Bonded Composite Repairs

Today’s bonded composite repairs rely heavily on manually grinding. The human influence on scarf tolerances and consequently on assembly and structural performance can be reduced by automating the process of scarf manufacturing. A process based on contact free surface scanning, surface reconstruction, automated repair design and automated milling of the repair scarf is presented. A machine and software design for validation purposes is described. Several repair specific design considerations relevant for the construction of a mobile scarfing machine are discussed. The redesign of a standard 3-axis milling machine to a mobile automated scarfing unit is presented and the architecture of the associated software framework described. An outlook to future validation steps is given

Actuation mechanisms of carbon nanotube-based architectures

State of the art smart materials such as piezo ceramics or electroactive polymers cannot feature both, mechanical stiffness and high active strain. Moreover, properties like low density, high mechanical stiffness and high strain at the same time driven by low energy play an increasingly important role for their future application. Carbon nanotubes (CNT), show this behavior. Their active behavior was observed 1999 the first time using paper-like mats made of CNT. Therefore the CNT-papers are electrical charged within an electrolyte thus forming a doublelayer. The measured deflection of CNT material is based on the interaction between the charged high surface area formed by carbon nanotubes and ions provided by the electrolyte. Although CNT-papers have been extensively analyzed as well at the macro-scale as nano-scale there is still no generally accepted theory for the actuation mechanism. This paper focuses on investigations of the actuation mechanisms of CNT-papers in comparison to vertically aligned CNT-arrays. One reason of divergent results found in literature might be attributed to different types of CNT samples. While CNT-papers represent architectures of short CNTs which need to bridge each other to form the dimensions of the sample, the continuous CNTs of the array feature a length of almost 3 mm, along which the experiments are carried out. Both sample types are tested within an actuated tensile test set-up under different conditions. While the CNT-papers are tested in water-based electrolytes with comparably small redox-windows the hydrophobic CNT-arrays are tested in ionic liquids with comparatively larger redox-ranges. Furthermore an in-situ micro tensile test within an SEM is carried out to prove the optimized orientation of the MWCNTs as result of external load. It was found that the performance of CNT-papers strongly depends on the test conditions. However, the CNT-arrays are almost unaffected by the conditions showing active response at negative and positive voltages. A micro alignment as result of tensile stress can be proven. A comparison of both results point out that the actuation mechanism strongly depends on the weakest bonds of the architectures: Van-der-Waals-bonds vs. covalent C-bond

Sensor Design Optimization for Ultrasonic Spectroscopy Cure Monitoring

In the field of cure monitoring, resonant ultrasonic cure monitoring is a unique technique to measure the progression of cure of composites in fully or partially closed tools. It allows for the use of electronic hardware that is less sophisticated than traditional pulse-based ultrasonic systems to obtain accurate results. While this technique is not new, it has been used very rarely. One reason for this is the lack of optimized sensors. Commercially available sensors are optimized for pulse-based ultrasonic testing. This paper establishes a possible optimized sensor design for resonant ultrasound cure monitoring using a multi-parameter FE model

Pulse Ultrasonic Cure Monitoring of the Pultrusion Process

This article discusses the results of a series of experiments on pulse ultrasonic cure monitoring of carbon fiber reinforced plastics applied to the pultrusion process. The aim of this study is to validate the hypothesis that pulse ultrasonic cure monitoring can be applied (a) for profiles having small cross sections such as 7 mm 0.5 mm and (b) within the environment of the pultrusion process. Ultrasonic transducers are adhesively bonded to the pultrusion tool as actuators and sensors. The time-of-flight and the amplitude of an ultrasonic wave are analyzed to deduce the current curing state of the epoxy matrix. The experimental results show that ultrasonic cure monitoring is indeed applicable even to very thin cross sections. However, significant challenges can be reported when the techniques are used during the pultrusion process

A Novel Approach to Monitoring the Curing of Epoxy in Closed Tools by Use of Ultrasonic Spectroscopy

The increasing use of composite materials has led to a greater demand for efficient curing cycles to reduce costs and speed up production cycles in manufacturing. One method to achieve this goal is in-line cure monitoring to determine the exact curing time. This article proposes a novel method through which to monitor the curing process inside closed tools by employing ultrasonic spectroscopy. A simple experiment is used to demonstrate the change in the ultrasonic spectrum during the cure cycle of an epoxy. The results clearly reveal a direct correlation between the amplitude and state of cure. The glass transition point is indicated by a global minimum of the reflected amplitude

Influence of fused deposition modeling process parameters on the transformation of 4D printed morphing structures

4D printing combines additive layer manufacturing processes with smart materials to create structures that are able to change shape or properties over time under the influence of environmental stimuli. The article presents 3D printed multi-material shape-variable structures imitating a hinge. Fused deposition modelling was used because it provides the ability to preprogram structures during the printing process by varying printing parameters. The structures are printed with PLA and TPU and remain flat after printing until they are exposed to a stimulus - heat. The main objective of this article is to present the possibilities of the aforementioned preprogramming step which can be adapted by varying the printing process and design parameters of the printed part. Experimental results are presented investigating the influence of printing speed, temperature of the build plate and number of active layers in the structure. Furthermore, the repeatability of deformations after a small number of cycles is investigated. The obtained results prove that the deformation of the structures can be controlled by printing parameters and a variety of bending degrees can be obtained by manipulating them. Hot water is used as a stimulus in the study to activate the structures but it is believed that other direct and indirect heating sources are also applicable. The research could help predict the behaviour of deformation of shape-morphing structures by selecting certain printing and design parameter values

Design of a Herringbone-Grooved Bearing for Application in an Electrically Driven Air Compressor

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study

Transient Dynamic System Behavior of Pressure Actuated Cellular Structures in a Morphing Wing

High aspect ratio aircraft have a significantly reduced induced drag, but have only limited installation space for control surfaces near the wingtip. This paper describes a multidisciplinary design methodology for a morphing aileron that is based on pressure-actuated cellular structures (PACS). The focus of this work is on the transient dynamic system behavior of the multi-functional aileron. Decisive design aspects are the actuation speed, the resistance against external loads, and constraints preparing for a future wind tunnel test. The structural stiffness under varying aerodynamic loads is examined while using a reduced-order truss model and a high-fidelity finite element analysis. The simulations of the internal flow investigate the transient pressurization process that limits the dynamic actuator response. The authors present a reduced-order model based on the Pseudo Bond Graph methodology enabling time-efficient flow simulation and compare the results to computational fluid dynamic simulations. The findings of this work demonstrate high structural resistance against external forces and the feasibility of high actuation speeds over the entire operating envelope. Future research will incorporate the fluid–structure interaction and the assessment of load alleviation capability