Numerical simulation of abrupt contraction flows using the Double Convected Pom-Pom model

The Double Convected Pom-Pom model was recently introduced to circumvent some numerical and theological defects found in other formulations of the Pom-Pom concept. It is used here for the simulation of a benchmark problem: the flow in an abrupt planar contraction. The predictions are compared with birefringence measurements and show reasonable quantitative agreement with experimental data. A parametric study is also carried out with the aim of analysing the effect of the branching parameter on vortex dynamics and extrudate swell. The results show that the Double Convected Pom-Pom model (DCPP) model is able to discriminate between branched and linear macromolecular structures in accordance with experimental observations. In that respect, the role of the extensional properties in determining complex flow behaviour is stressed. Also, the ratio of the first normal stress difference to the shear stress appears to play a major role in die swell observation. For the time being, the role of the second normal stress difference appears to be less obvious to evaluate in this complex flow. (C) 2004 Elsevier B.V. All rights reserved.

Control of hypersonic turbulent skin friction by boundary-layer combustion of hydrogen

Shvab-Zeldovich coupling of flow variables has been used to extend Van Driest's theory of turbulent boundary-layer skin friction to include injection and combustion of hydrogen in the boundary layer. The resulting theory is used to make predictions of skin friction and heat transfer that are found to be consistent with experimental and numerical results. Using the theory to extrapolate to larger downstream distances at the same experimental conditions, it is found that the reduction in skin-friction drag with hydrogen mixing and combustion is three times that with mixing alone. In application to flow on a flat plate at mainstream velocities of 2, 4, and 6 knits, and Reynolds numbers from 3 X 10(6) to 1 x 10(8), injection and combustion of hydrogen yielded values of skin-friction drag that were less than one-half of the no-injection skin-friction drag, together with a net reduction in heat transfer when the combustion heat release in air was less than the stagnation enthalpy. The mass efficiency of hydrogen injection, as measured by effective specific impulse values, was approximately 2000 s.

Potential to increase yield in lucerne (Medicago sativa subsp sativa) through introgression of Medicago sativa subsp falcata into Australian adapted material

The effect of interspecific heterosis in crosses between Medicago sativa subsp. sativa and M. sativa subsp. falcata was assessed. Three sativa and 3 falcata plants were crossed in a diallel design. Progeny dry matter yield and natural plant height were assessed in a replicated field experiment at Gatton, Queensland. Yield data were analysed using the method of residual maximum likelihood (REML) and Griffing's model 1. There were significant differences between the reciprocal, general combining ability (GCA), and specific combining ability (SCA) effects. As expected, S-1 populations were lower yielding than their respective intraspecific cross and falcata x falcata crosses were significantly lower yielding than sativa x sativa crosses. Some of the interspecific crosses indicated substantial SCA effects, yielding at least as well as the best sativa x sativa crosses. We have demonstrated the potential usefulness of unselected M. sativa subsp. falcata as a heterotic group in the improvement of yield in northern Australian adapted lucerne material, and discuss how it could be incorporated into future breeding to overcome the yield stagnation currently being experienced in Australian programs.

Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

Simulations of a complete reflected shock tunnel facility have been performed with the aim of providing a better understanding of the flow through these facilities. In particular, the analysis is focused on the premature contamination of the test flow with the driver gas. The axisymmetric simulations model the full geometry of the shock tunnel and incorporate an iris-based model of the primary diaphragm rupture mechanics, an ideal secondary diaphragm and account for turbulence in the shock tube boundary layer with the Baldwin-Lomax eddy viscosity model. Two operating conditions were examined: one resulting in an over-tailored mode of operation and the other resulting in approximately tailored operation. The accuracy of the simulations is assessed through comparison with experimental measurements of static pressure, pitot pressure and stagnation temperature. It is shown that the widely-accepted driver gas contamination mechanism in which driver gas 'jets' along the walls through action of the bifurcated foot of the reflected shock, does not directly transport the driver gas to the nozzle at these conditions. Instead, driver gas laden vortices are generated by the bifurcated reflected shock. These vortices prevent jetting of the driver gas along the walls and convect driver gas away from the shock tube wall and downstream into the nozzle. Additional vorticity generated by the interaction of the reflected shock and the contact surface enhances the process in the over-tailored case. However, the basic mechanism appears to operate in a similar way for both the over-tailored and the approximately tailored conditions.

Generative acts: Family and community involvement of older Australians

The article adopts a developmental approach to successful human aging by exploring the concept of generativity in relation to a study of older Australians' lived experiences of involvement in the family and community. Qualitative data, collected through focus group interviews, were analyzed interpretively using recent developments in Erikson's theory of generativity as a framework. As a result, the present study contributes an in-depth understanding of the role of generative acts to the lives of older people. The data provide illustrative support for Erikson's contention of a generativity/stagnation crisis in later life. Involvement in the family and community is seen as a productive and generative activity, which promotes a positive experience of aging. Two further emergent themes are also explored. First, the experiences of study participants illustrate the reciprocal and cyclical nature of grand-generativity, and the importance of intergenerational relationships. Finally, the data contribute to our knowledge of cultural generativity, and in particular the passing on of cultural knowledge through narratives and modeling.