Active Flow Control at Low Reynolds Numbers by Periodic Airfoil Morphing

This paper investigates the application of a periodically deforming airfoil surface for the purpose of flow control at low Reynolds numbers. A physical model has been fabricated by bonding Macro Fiber Composite (MFC) actuators to the underside of a NACA 4415’s suction surface. The results presented build on work by Jones et al.1 First, the behavior of the surface when actuated at a range frequencies is investigated through a combination of photogrammetric and laser sensor measurements. Second, the aerodynamic performance of this novel flow control technique is presented. It is shown that when the actuation frequency ‘locks-in’ to the surface motion significant improvements in performance are observed in a flight regime notorious for poor airfoil behavior

On orbit validation of solar sailing control laws with thin-film spacecraft

Many innovative approaches to solar sail mission and trajectory design have been proposed over the years, but very few ever have the opportunity to be validated on orbit with real spacecraft. Thin- Film Spacecraft/Lander/Rovers (TF-SL Rs) are a new class of very low cost, low mass space vehicle which are ideal for inexpensively and quickly testing in flight new approaches to solar sailing. This paper describes using TF- SLR based micro solar sails to implement a generic solar sail test bed on orbit. TF -SLRs are high area- to-mass ratio (A/m) spacecraft developed for very low cost consumer and scientific deep space missions. Typically based on a 5 μm or thinner metalised substrate, they include an integrated avionics and payload system -on-chip (SoC) die bonded to the substrate with passive components and solar cells printed or deposited by Metal Organic Chemical Vapour Deposition (MOCVD). The avionics include UHF/S- band transceivers, processors, storage, sensors and attitude control provided by integrated magnetorquers and reflectivity control devices. Resulting spacecraft have a typical thickness of less than 50 μm, are 80 mm in diameter, and have a mass of less than 100 mg resulting in sail loads of less than 20 g/m 2 . TF -SLRs are currently designed for direct dispensing in swarms from free flying 0.5U Interplanetary CubeSats or dispensers attached to launch vehicles. Larger 160 mm, 320 mm and 640 mm diameter TF -SLRs utilizing a CubeSat compatible TWIST deployment mechanism that maintains the high A/m ratio are also under development. We are developing a mission to demonstrate the utility of these devices as a test bed for experimenting with a variety of mission designs and control laws. Batches of up to one hundred TF- SLRs will be released on earth escape trajectories, with each batch executing a heterogeneous or homogenous mixture of control laws and experiments. Up to four releases at different points in orbit are currently envisaged with experiments currently being studied in MATLAB and GMA T including managing the rate of separation of individual spacecraft, station keeping and single deployment/substantially divergent trajectory development. It is also hoped to be able to demonstrate uploading new experiment designs while in orbit and to make this capability available to researchers around the world. A suitable earth escape mission is currently being sought and it is hoped the test bed could be on orbit in 2017/18

Wind Tunnel Experiments with Flexible Plates in Transonic Flows

The evolution of adaptive shock control bump (SCB) design has seen the system flexibility increase to a point where the aerodynamic loading can affect the deformation of the plate. By studying the effects of a flexible plate subject to transonic flow the fluid structure interaction can be investigated. In this study an array of thin plates (0.4 and 0.6 mm) with different aspect ratios (1 and 1.33) are exposed to a Mach 1.4 normal shockwave. PIV is used in combination with Schlieren imaging to provide a detailed view of the flow curvature surrounding the plate as well as the global shock structure. A technique that extracts the plate deformation from the PIV images is also presented which provides fluid and structural information for each test. The relationship between plate and flow angle is discussed as well as the effect of plate stiffness and free stream influence of each plate configuration

Topological optimization of compliant adaptive wing structure

Load-path-based topology optimization is used to synthesize a compliant adaptive aircraft wing leading edge, which deforms in a prescribed way when subject to a single point internal actuation. The load-path-based optimization method requires the specification of a parent lattice. Increasing the complexity of this lattice means the number of parameters required for a complete representation of the structure in the topology optimization becomes prohibitive, although it is desirable to enable a full exploration of the design space. A new method based on graph theory and network analysis is proposed, which enables a substantial reduction in the required number of parameters to represent the parent lattice. The results from this load-path-based approach are compared with those obtained from the better-known density-based topology optimization method

Experimental FSI study of adaptive shock control bumps

The shock stabilisation and wave drag reduction potential of a two-dimensional adaptive shock control bump has been studied in the Imperial College supersonic wind tunnel. The bump was modelled as a flexible aluminium alloy plate deformed through spanwise actuation, and several bump heights were tested beneath a Mach 1.4 transonic shock wave. Schlieren images and static pressure readings along the flexible plate allowed the study of the λλ-shock structure generated by the bifurcation of the normal shock for a range of shock positions. All bumps tested were found to increase shock stability, but wave drag reduction was only observed for shocks close to the leading edge of the flexible plate. Positive deformations of the flexible plate for downstream shocks are believed to reduce supersonic flow reacceleration, and hence the strength of the rear leg of the λλ-shock and wave drag, in comparison to a solid bump with the same shape. The position of the rear leg of the λλ-shock was found to exhibit a bistable behaviour, and this is hypothesised to be caused by a complex coupling of aerodynamic and structural instabilities

Effects of Viscoelasticity on the Deployment of Bistable Tape Springs

The effects of stowage on the deployment of composite bistable tape springs are studied. A viscoelastic analytical model is used to predict the relaxation and stability of the structure in its coiled state. The time-dependent stability analysis reveals that the structure remains bistable throughout the relaxation process. A dynamic model is then applied to predict the deployment of the structure once it is released. Experimental deployment results match the deployment predictions within 3% for the case where no stowage is applied. It is shown that stowage causes an increase in the deployment time; in this case, experimental deployment times overshoot those predicted by the model. Secondary effects are observed at high stowage temperatures, which are not predicted by the analytical model. These effects include an abrupt change in the deployment dynamics and a large increase in the deployment time (deployment latency). At higher temperatures still, i.e. for stowage at 100°C, the structure fails to deploy and becomes stable at all extended lengths

Optical response of two-dimensional electron fluids beyond the Kohn regime: strong non-parabolic confinement and intense laser light

We investigate the linear and non-linear optical response of two-dimensional (2D) interacting electron fluids confined by a strong non-parabolic potential. We show that such fluids may exhibit higher-harmonic spectra under realistic experimental conditions. Higher harmonics arise as the electrons explore anharmonicities of the confinement potential (electron-electron interactions reduce this non-linear effect). This opens the possibility of controlling the optical functionality of such systems by engineering the confinement potential. Our results were obtained within time-dependent density-functional theory, employing the adiabatic local-density approximation. A classical hydrodynamical model is in good agreement with the quantum-mechanical results.Comment: 4 pages, 4 figure

‘It's like the bad guy in a movie who just doesn't die’ : a qualitative exploration of young people's adaptation to eczema and implications for self‐care

Background Eczema is a common childhood inflammatory skin condition, affecting more than one in five children. A popular perception is that children ‘outgrow eczema’, although epidemiological studies have shown that, for many, eczema follows a lifelong episodic course. Objectives To explore the perceptions of young people about the nature of their eczema and how these perceptions relate to their self‐care and adapting to living with eczema. Methods This is a secondary inductive thematic analysis of interviews conducted for Healthtalk.org. In total 23 interviews with young people with eczema were included. Of the 23 participants, 17 were female and six male, ranging from 17 to 25 years old. Results Participants generally experienced eczema as an episodic long‐term condition and reported a mismatch between information received about eczema and their experiences. The experience of eczema as long term and episodic had implications for self‐care, challenging the process of identifying triggers of eczema flare‐ups and evaluating the success of treatment regimens. Participants’ experiences of eczema over time also had implications for adaptation and finding a balance between accepting eczema as long term and hoping it would go away. This linked to a gradual shift in treatment expectations from ‘cure’ to ‘control’ of eczema. Conclusions For young people who continue to experience eczema beyond childhood, a greater focus on self‐care for a long‐term condition may be helpful. Greater awareness of the impact of early messages around ‘growing out of’ eczema and provision of high‐quality information may help patients to manage expectations and support adaptation to treatment regimens