A wake model for free-streamline flow theory. Part 1. Fully and partially developed wake flows and cavity flows past an oblique flat plate

A wake model for the free-streamline theory is proposed to treat the two-dimensional flow past an obstacle with a wake or cavity formation. In this model the wake flow is approximately described in the large by an equivalent potential flow such that along the wake boundary the pressure first assumes a prescribed constant under-pressure in a region downstream of the separation points (called the near-wake) and then increases continuously from this under-pressure to the given free-stream value in an infinite wake strip of finite width (the far-wake). Application of this wake model provides a rather smooth continuous transition of the hydrodynamic forces from the fully developed wake flow to the fully wetted flow as the wake disappears. When applied to the wake flow past an inclined flat plate, this model yields the exact solution in a closed form for the whole range of the wake under-pressure coefficient

Climate in the balance

This essay explores how our climate system works, how humans are changing the climate system, and how we might face the challenges of reducing our negative impact on the climate system in the future

Dermophis oaxacae

Number of Pages: 2Integrative BiologyGeological Science

On the estimation of swimming and flying forces from wake measurements

The transfer of momentum from an animal to fluid in its wake is fundamental to many swimming and flying modes of locomotion. Hence, properties of the wake are commonly studied in experiments to infer the magnitude and direction of locomotive forces. The determination of which wake properties are necessary and sufficient to empirically deduce swimming and flying forces is currently made ad hoc. This paper systematically addresses the question of the minimum number of wake properties whose combination is sufficient to determine swimming and flying forces from wake measurements. In particular, it is confirmed that the spatial velocity distribution (i.e. the velocity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with the fluid pressure distribution. Importantly, it is also shown that the spatial distribution of rotation and shear (i.e. the vorticity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with a parameter that is analogous to the fluid pressure. The measurement of this parameter in the wake is shown to be identical to a calculation of the added-mass contribution from fluid surrounding vortices in the wake, and proceeds identically to a measurement of the added-mass traditionally associated with fluid surrounding solid bodies. It is demonstrated that the velocity/pressure perspective is equivalent to the vorticity/vortex-added-mass approach in the equations of motion. A model is developed to approximate the contribution of wake vortex added-mass to locomotive forces, given a combination of velocity and vorticity field measurements in the wake. A dimensionless parameter, the wake vortex ratio (denoted Wa), is introduced to predict the types of wake flows for which the contribution of forces due to wake vortex added-mass will become non-negligible. Previous wake analyses are reexamined in light of this parameter to infer the existence and importance of wake vortex added-mass in those cases. In the process, it is demonstrated that the commonly used time-averaged force estimates based on wake measurements are not sufficient to prove that an animal is generating the locomotive forces necessary to sustain flight or maintain neutral buoyancy

Student performance standards and Queensland teacher education

This paper considers the implementation of Student Performance Standards (SPS) in Queensland, Australia, and their implications for teacher education. Student testing procedures in various Australian states and territories are described. A theoretical framework, grounded in Australian educational history, is elaborated for understanding the political ramifications of SPS. S. J. Ball's explication of market, management and, particularly, curriculum controls over public education is applied to show how explicit emphasis on student performance is linked to wider forces promoting an instrumentalist and managerialist view of schooling. The emergence of statewide testing is seen as: a quality control measure designed to ensure that schools are producing human resources tailored to the needs of a post-fordist economy; an attempt to shape the quality, character, and content of classroom practice; and a potential step toward monitoring the performance of teachers and schools, making comparisons among them, and linking these comparisons to performance-related pay awards. The paper concludes that SPS constitutes a not entirely desirable response to a series of complex educational and political changes within and outside Australia. SPS represents in microcosm what is a broader challenge to the celebration of diversity and the recognition of heterogeneity that ought to underpin any teacher education program. (Contains 16 references.