Skin friction drag reduction over staggered three dimensional cavities

The effect of three-dimensional staggered circular cavities on a zero-pressure gradient incompressible turbulent boundary layer was studied. Two key parameters were varied, being the ratio of the diameter, d, to the depth, h, of the cavity, d/h and the Reynolds number based on the diameter of the cavity, Rd. Velocity profile measurements showed that for the cases of d/h>1 an increase in skin friction drag was experienced with respect to a smooth surface, but for d/h≤1 the drag increment was almost negligible and in some cases it was lower than that of a smooth surface by up to 10%. Measurements along the spanwise plane showed the presence of organised transverse velocity components which bear some resemblance with the flow over riblets. The skin friction drag appears to be a strong function of Rd, where for Rd>5500 a drag increment is experienced which could potentially be due to shear layer breakdown and more production of turbulence

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

Family support and cardiac rehabilitation: A comparative study of the experiences of South Asian and White-European patients and their carer's living in the United Kingdom

Background: Effective lifestyle modification facilitated by cardiac rehabilitation is known to reduce the occurrence of adverse coronary events and mortality. South Asians have poorer outcomes after a myocardial infarction than the general UK population, but little is known about their experiences of family support, cardiac rehabilitation and lifestyle change. Aims: To explore the nature of family support available to a sample of South Asian and White-European cardiac patients and to highlight similarities and differences between these groups with regard to cardiac rehabilitation and lifestyle modification. Methods: Using a qualitative approach, semi-structured interviews (in 1 of 6 languages) were conducted by researchers with; 45 South Asian patients and 37 carers and 20 White-European patients and 17 carers. Interviews were conducted in a home setting, up to eighteen months after discharge from hospital following myocardial infarction, coronary artery bypass surgery or unstable angina. Results: The main themes that emerged related to the provision of advice and information, family support and burden, dietary change and exercise regimes. Conclusions: Several cultural and ethnic differences were identified between patients and their families alongside similarities, irrespective of ethnicity. These may represent generic characteristics of recovery after a cardiac event. Health professionals should develop a cultural repertoire to engage with diversity and difference. Not every difficulty a person encounters as they try to access appropriate service delivery can be attributed to ethnic background. By improving services generally, support for South Asian populations can be improved. The challenge is to know when ethnicity makes a difference and mediates a person's relationship with service support and when it does not. (C) 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved

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