Measurement and modelling of the turbulent boundary layer near the attachment line of a swept wing

This work is motivated by the need for low-order aerodynamic models to predict accurately the effect on profile drag of controlling attachment line transition. Head's entrainment method (1) , a rapid integral boundary layer technique used for design studies on swept wings, suffers from the governing swept-tapered turbulent integral boundary layer equations being ill-posed in the vicinity of the attachment line. This singularity has been treated using crude extrapolations of the attachment-line similarity solution for over half a century, but this approach is unlikely to deliver accurate predictions of the effect of changes in the attachment line flow on profile drag. An experimental study has been carried out to explore the nature of the turbulent flow in the vicinity of a highly swept swept attachment line and has revealed a quite complex, non-monotonic development of the momentum thickness in this region. It has also revealed lower levels of twist in the boundary layer velocity profiles than anticipated from the highly curved character of the inviscid flow streamlines. These observations have prompted an alternative approach to the modelling of the flow in this region which not only successfully eliminates the lack of robustness in the swept-tapered equations but which also matches the experimental results to within ±5%

Incompressible turbulent flow at the leading edge of swept wings

Due to a singularity in the governing three-dimensional turbulent momentum integral equations at the attachment line, low order infinite-swept and swept-tapered CFD methods employing the viscous-coupling technique have been unable to model attachment line transition or contamination without approximating the development of the boundary layer immediately downstream of a turbulent attachment line. An experimental study was therefore conducted to explore the flow near a turbulent attachment line, which showed considerable differences to the numerical approximation. On the basis of the experimental data; a modification to the governing equations in the attachment line region has been proposed and tested. Comparisons with experimental measurements show that the proposed numerical model is not only able to predict the flow to within ±5%, but it also captures the non-monotonic behaviour of the momentum thickness, in the vicinity of the attachment line, which has not been reported previously

Recent Developlments to the viscous Garabedian and Korn method

This paper describes recent developments to the legacy VGK method based upon a new coupling with the Callisto boundary layer code developed for Airbus. The new CVGK method has been compared against its predecessor and validated against a transonic swept-wing dataset. Various conceptual studies have then been carried out to model the effect on form drag (viscous pressure drag) of changes to boundary layer entrainment and shock-control ramps. It is concluded that there are both risks to, and opportunities for, drag reduction techniques associated with managing the form drag contribution from the aft region of highly-loaded transonic aerofoils

'A light in a very dark place' : The role of a voluntary organisation providing support for those affected by encephalitis

Voluntary organisations are seen as contributing to the ‘democratisation’ of health and social care. Little, however, is written about their role and this paper, by focusing on the work of The Encephalitis Society, provides insights into the challenges facing voluntary organisations as they manage twin roles as service providers and advocates, of people with neurological disorders. Two studies are presented: a review conducted by the Society, focusing on patient’s experiences of neurological services; and an external evaluation of the Society’s current provision. The first, based on a postal survey of its members affected by encephalitis (n = 339), illustrates the Society’s advocacy role. The survey provided support for the Association of British Neurologists’ recommendation for nationally agreed standards of care. The second study, a postal survey of recent contacts (n = 76) and in-depth telephone interviews (n = 22), illustrates the Society’s value role as a service provider and supports its role in helping rehabilitate affected individuals and their families. These studies provided the Society with information for policy and service development. Importantly, providing the basis of informed action and partnership with stakeholders and informing the organisation’s sense of purpose, in the changing context of welfare provision in the UK

An Age Old Problem? Estimating the Impact of Dementia on Past Human Populations.

OBJECTIVE: To model the impact of dementia on past societies. METHOD: We consider multiple lines of evidence indicating elderly individuals to have been more common throughout the past than is frequently accepted. We then apply known dementia incidence/prevalence rates to plausible assumptions of past population structures to suggest prevalence in the past. RESULTS: Dementia prevalence in premodern societies is likely to have been around 5% of the rate seen in modern, developed countries but with a total past incidence running into billions. DISCUSSION: Dementia is often seen as a "modern" challenge that humans have not had to contend with before. We argue that this condition has had considerably greater effects than previously envisaged and is a challenge that humans have already withstood successfully, on one hand at a lower incidence but on the other without the considerable clinical, technological, and social advances that have been made in recent times

The trade-off between taxi time and fuel consumption in airport ground movement

Environmental impact is a very important agenda item in many sectors nowadays, which the air transportation sector is also trying to reduce as much as possible. One area which has remained relatively unexplored in this context is the ground movement problem for aircraft on the airport’s surface. Aircraft have to be routed from a gate to a runway and vice versa and it is still unknown whether fuel burn and environmental impact reductions will best result from purely minimising the taxi times or whether it is also important to avoid multiple acceleration phases. This paper presents a newly developed multi-objective approach for analysing the trade-off between taxi time and fuel consumption during taxiing. The approach consists of a combination of a graph-based routing algorithm and a population adaptive immune algorithm to discover different speed profiles of aircraft. Analysis with data from a European hub airport has highlighted the impressive performance of the new approach. Furthermore, it is shown that the trade-off between taxi time and fuel consumption is very sensitive to the fuel-related objective function which is used

On the turbulent mean-flow at the leading edge of a swept wing

Due to the presence of a singularity in the governing three-dimensional (3D) momentum integral equation at the attachment line (AL) and numerical issues while marching immediately downstream, a numerical fix was previously imposed in the leading edge (LE) modelling of Airbus Callisto. This technique has been employed for half a century during the design and optimisation of transonic wings, but recent analysis on AL control for form drag reduction rose concerns about this previously accepted numerical fix. An experimental study was conducted to validate this LE approximation. Measurement of the boundary layer integral quantities immediately downstream of the AL showed considerable increment; therefore a modification to the 3D governing equation was suggested to remove the numerical fix in the LE modelling. Comparison with experimental measurements showed that the proposed numerical model is not only able to predict the flow within an agreement of ±5%, but it is also able to capture the non-monotonic behaviour in the development of the momentum thickness in the vicinity of the AL, not reported previously

On the excitation of Tollmien-Schlichting waves due to surface vibration

The effect of localised surface vibration on the stability of a Blasius boundary layer was studied. First it was demonstrated that small amplitude vibration of the order of less than 10µm can artificially excite Tollmien-Schlichting (TS) waves provided that the frequency of excitation was within the frequency band of the naturally occurring disturbance in the freestream environment. Longitudinally aligned motors generated more energetic TS wave and the growth rate increased with increasing number of live motors. But when a combination of both longitudinally and transversely align motors was tested a reduction in the growth rate was observed even when the total number of motors was larger than the most amplified case which was generated by 5 motors along the longitudinal axis

Development of a quantitative Schlieren imaging technicque for acoustic waves

The primary objective of the present work was the development of a quantitative schlieren-imaging technique that can be used to study the dynamics of instability waves. An underexpanded jet was considered as an ideal test case due to the complexity and multitude of instability mechanism. The technique was initially validated by optically capturing a controlled acoustic wave generated by a compression driver and excellent agreement was obtained with microphone measurements. Further analysis of an underexpanded jet demonstrated that the technique can be used to capture the very high screech frequency

A simple digital-optical system to improve accuracy of hot-wire measurements

A high precision traverse mechanism with micro-resolution was designed to capture accurately the velocity profile of the very thin turbulent attachment line on a swept body. To ensure that the traverse mechanism could position the hot wire reliably, a simple digital optical system was designed to check the performance of the traverse by measuring the displacement of the hot wire: a vertical displacement of 2.4µm was achievable and this could be further reduced to 0.6µm using micro-stepping. Due to the simplicity of the set-up it was equally useful for probe wall positioning and the velocity profiles captured clearly demonstrated that the optical set-up helped in resolving the near wall flow more accurately, regardless of the thinness of the boundary layer. The captured data compare well with the results from similar investigations, with arguably higher precision achieved