First a three-dimensional turbulent boundary-layer experiment is described. This has been carried out with the specific aim of providing a test-case for calculation methods. Much attention has been paid to the design of the test set-up. An infinite swept-wing flow has been simulated with good accuracy. The initially two-dimensional boundary layer on the test plate was subjected to an adverse pressure gradient, which led to three-dimensional separation near the trailing edge of the plate. Next, a calculation method for three-dimensional turbulent boundary layers is discussed. This solves the boundary-layer equations numerically by finite differences. The turbulent shear stress is obtained from a generalized version of Bradshaw's two-dimensional turbulent shear stress equation. The results of the calculations are compared with those of the experiment. Agreement is good over a considerable distance; but large discrepancies are apparent near the separation line.
This study is concerned with the effect of external turbulence on the decay of vortices. Single vortices and vortex pairs were generated with wing(s) mounted in the sidewalls of a wind tunnel. The distance between the two vortices could be adjusted such that they just touched each other or overlapped. The intensity of the turbulence could be controlled with a turbulence grid. The development of the vortex was measured at a number of downstream stations with particle image velocimetry for a range of wing settings. The results indicate that the single vortex can be described by the ‘two length scales’ model of Jacquin, Fabre & Geffroy (AIAA, vol. 1038, 2001, p. 1). A vortex core, which decays like a Lamb–Oseen vortex, is embedded in a region with an almost constant radius and a much lower azimuthal velocity that obeys a ~r−β power law, with r being the radius measured from the vortex centre. For the turbulence levels and the test section length used in this study, the single-vortex behaviour is independent of the external turbulence and in contrast with the decay of the vortex pair that strongly depends on the external turbulence. In the initial stages of the vortex pair evolution, the vortices decay due to cancellation of vorticity at the symmetry plane. At a later stage, Crow oscillations are observed, followed by a breakdown of the vortices. This vortex breakdown might be due to direct turbulent action. The observed behaviour is in agreement with the theoretical model of Crow & Bate (J. Aircraft, vol. 13, 1976, p. 476).
Facial neuromuscular electrical stimulation (fNMES), which allows for the non-invasive and physiologically sound activation of facial muscles, has great potential for investigating fundamental questions in psychology and neuroscience, such as the role of proprioceptive facial feedback in emotion induction and emotion recognition, as well as for clinical applications, such as alleviating depression symptoms. However, despite illustrious origins in 19th century work of Duchenne de Boulogne, the practical application of fNMES remains largely unknown to researchers in psychology and human physiology. In addition, published studies vary dramatically in use and reporting of parameters, such as stimulation frequency, amplitude, duration, and electrode size. Because fNMES parameters impact the comfort and safety of volunteers, as well as its physiological (and psychological) effects, it is of paramount importance to establish recommendations of good practice. Here, we provide an introduction to fNMES, a systematic review of the existing literature focusing on stimulation parameters used, and we offer recommendations on how to safely and reliably deliver fNMES. In addition, we provide a free webpage, allowing to easily verify and compare the safety of fNMES parameters based on current density. As an example of a potential application, we focus on the use of fNMES for the investigation of the facial feedback hypothesis.
Ladies and gentlemen, it is an honour and a great pleasure to present this Lanchester Memorial Lecture. I thank the Royal Aeronautical Society and its Aerodynamic Committee for inviting me. In preparing this lecture I greatly enjoyed the added significance of presenting it in the historical context set by Lanchester. But the real pleasure is to be here among many good friends with whom I worked together for shorter or longer periods. “A body that in its motion through a fluid does not give rise to a surface of discontinuity.” So Lanchester defined a ‘ streamline body’ in his standard work Aerodynamics. With ‘ discontinuity’ the boundary is meant between the outer flow and the dead water region formed by fluid that departs from the surface as illustrated nicely in Fig. 1 for the flow around a cylinder.
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