Experimental data and model for the turbulent boundary layer on a convex, curved surface

Experiments were performed to determine how boundary layer turbulence is affected by strong convex curvature. The data gathered on the behavior of the Reynolds stress suggested the formulation of a simple turbulence model. Data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero. Two experiments were performed at delta/R approximately 0.10, and one at weaker curvature with delta/R approximately 0.05. Results show that after a sudden introduction of curvature the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. When the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions. A simple turbulence model, which was based on the theory that the Prandtl mixing length in the outer layer should scale on the velocity gradient layer, was shown to account for the slow recovery

Epidemiological aspects of circulatory disease in Scotland

Epidemiology is defined as the medicine of populations rather than, individuals. The thesis deals with the pattern of mortality from cerebrovascular disease in Scotland, England and Wales; the investigation of some possibilities in screening for symptoms of cerebrovascular disease; and a study of blood pressure on the Hebridean Island of Tiree. Chapter I. A Short History of Epidemiology. Chapter II. The Mature of Mortality Data, for Cerebrovascular Disease. As approximately fifty per cent of deaths from cerebrovascular disease take place at home and grouped data show that hospital clinicians have difficulty in distinguishing between cerebral haemorrhage and infarction, death certificate data for these categories of disease are likely to be unreliable. While this finding is supported from the literature, factors which enhance the validity of death certificates for cerebrovascular-disease are discussed and evidence produced indicating ways in which such data may be considered of greater consequence. Chapter III. The Pattern of Nortality from Cerebrovascular Disease and Arteriosclerotic and Degenerative Heart Disease in Scotland, England and Wales (1947-1966). The crude and direct standardised mortality rates for males and females by five year age groups for cerebrovascular disease (I.S.C. 330-334 and 330, 331, 332) and arteriosclerotic and degenerative heart disease (I.S.C. 420-422) axe tabulated for the period 1947-1966 and the data of greatest interest presented in graphical form. Attention is drawn to the apparent recent lack of increase in mortality for cerebral infarction which is in marked contrast to the rise in rates for myocardial infarction especially in the population aged 50-64 years. The relationship of the two conditions is brought into question. Chapter V, The Introduction of a Questionary on Screening for Symptoms of Transient Cerebral Ischaemia. The cardio-respiratory screening unit and its method of operation is described. A simple questionary on loss of power in the upper and lower limbs and on loss of speech and consciousness is evolved, tested and considered suitable for interviewer - administration under the conditions of a screening survey. Chapter VI. An Account of the Administration of the Questionary on Symptoms of Transient Cerebral Ischaemia in Three Samples of the Scottish Population - Clackmannan, Glasgow and Tiree. Individuals v/ho have experienced one or more of the symptoms sought by the questionary have greater experience of symptoms of angina, infarction and claudication and also more signs of electrocardiographic abnormalities as well as greater experience of cigarette smoking than those who have not admitted to such symptoms. If the high prevalence of these symptoms is substantiated this may partially account for the lack of increase in rates for cerebral infarction and the rise in rates for myocardial infarction mentioned in Chapter III. This project is presently being followed-up by a case/control study and a record linkage procedure. Chapter VI. Blood Pressure in a Scottish Island Community. A study of mean blood pressure levels in age-and-sex-matched samples of the population of the Hebridean Island of Tiree appears to support the local belief that blood pressure is higher on the island than on the mainland. This conclusion may be related to the observation of a greater mean' width of the heart measured radiologically in the island population compared with the mainland population. Chapter VIII. The Paradox of Tiree. The Islanders of Tiree appear to have a greater experience of clinical signs of vascular disease while admitting to fewer symptoms than their mainland contemporaries. While mean blood pressure levels are generally higher for those with symptoms and signs of vascular disease than for those without, they occur at higher mean levels of blood pressure in the island population compared to the mainland. Those without symptoms or signs can have higher blood pressure on the island than those with symptoms on the mainland. The hypothesis that island life may protect the individual from the effects of raised blood pressure is explored but not proven. Chapter IX Summary

Operation of the computer model for direct atomic oxygen exposure of Earth satellites

One of the primary causes of material degradation in low Earth orbit (LEO) is exposure to atomic oxygen. When atomic oxygen molecules collide with an orbiting spacecraft, the relative velocity is 7 to 8 km/sec and the collision energy is 4 to 5 eV per atom. Under these conditions, atomic oxygen may initiate a number of chemical and physical reactions with exposed materials. These reactions contribute to material degradation, surface erosion, and contamination. Interpretation of these effects on materials and the design of space hardware to withstand on-orbit conditions requires quantitative knowledge of the atomic oxygen exposure environment. Atomic oxygen flux is a function of orbit altitude, the orientation of the orbit plan to the Sun, solar and geomagnetic activity, and the angle between exposed surfaces and the spacecraft heading. We have developed a computer model to predict the atomic oxygen exposure of spacecraft in low Earth orbit. The application of this computer model is discussed

Coaxial Jets with Disparate Viscosity: Mixing and Laminarization Characteristics

Mixing of fluids in a coaxial jet is studied under four distinct viscosity ratios, m = 1, 10, 20 and 40, using highly resolved large-eddy simulations (LES), particle image velocimetry and planar laser-induced fluorescence. The accuracy of predictions is tested against data obtained by the simultaneous experimental measurements of velocity and concentration fields. For the highest and lowest viscosity ratios, standard RANS models with unclosed terms pertaining to viscosity variations are employed. We show that the standard Reynolds-averaged Navier-Stokes (RANS) approach with no explicit modelling for variable-viscosity terms is not applicable whereas dynamic LES models provide high-quality agreement with the measurements. To identify the underlying mixing physics and sources of discrepancy in RANS predictions, two distinct mixing modes are defined based on the viscosity ratio. Then, for each mode, the evolution of mixing structures, momentum budget analysis with emphasis on variable-viscosity terms, analysis of the turbulent activity and decay of turbulence are investigated using highly resolved LES data. The mixing dynamics is found to be quite distinct in each mixing mode. Variable viscosity manifests multiple effects that are working against each other. Viscosity gradients induce additional instabilities while increasing overall viscosity decreases the effective Reynolds number leading to laminarization of the turbulent jet, explaining the lack of dispersion and turbulent diffusion. Momentum budget analysis reveals that variable-viscosity terms are significant to be neglected. The scaling of the energy spectrum cascade suggests that in the TLL mode the unsteady laminar shedding is responsible for the eddies observed

Systematics and Palynology of Picrodendron Further Evidence for Relationship with the Oldfieldioideae (Euphorbiaceae)

Although known to botanical science for 285 years, the genus Picrodendron Planchon has been poorly understood for most of this time. The most pervasive problem has been that of discerning familial relationships, and there have been additional difficulties in typifying the generic name (Hayden & Reveal, 1980) and in distinguishing its three nominate species. This paper provides a systematic treatment for Picrodendron and demonstrates its relationships with Euphorbiaceae subfam. Oldfieldioideae Kohler & Webster as evidenced by data on gross morphology, palynology, anatomy, and cytology