Determination of the decay exponent in mechanically stirred isotropic turbulence

Direct numerical simulation is used to investigate the decay exponent of isotropic homogeneous turbulence over a range of Reynolds numbers sufficient to display both high and low Re number decay behavior. The initial turbulence is generated by the stirring action of the flow past many small randomly placed cubes. Stirring occurs at 1/30 th of the simulation domain size so that the low-wavenumber and large scale behavior of the turbulent spectrum is generated by the fluid and is not imposed. It is shown that the decay exponent in the resulting turbulence matches the theoretical predictions for a k 2 low-wavenumber spectrum at both high and low Reynolds numbers. The transition from high Reynolds number behavior to low Reynolds number behavior occurs relatively abruptly at a turbulent Reynolds number of around 250 (Re λ

Computer design of microfluidic mixers for protein/RNA folding studies

Kinetic studies of biological macromolecules increasingly use microfluidic mixers to initiate and monitor reaction progress. A motivation for using microfluidic mixers is to reduce sample consumption and decrease mixing time to microseconds. Some applications, such as small-angle x-ray scattering, also require large ( \u3e 10 micron) sampling areas to ensure high signal-to-noise ratios and to minimize parasitic scattering. Chaotic to marginally turbulent mixers are well suited for these applications because this class of mixers provides a good middle ground between existing laminar and turbulent mixers. In this study, we model various chaotic to marginally turbulent mixing concepts such as flow turning, flow splitting, and vortex generation using computational fluid dynamics for optimization of mixing efficiency and observation volume. Design iterations show flow turning to be the best candidate for chaotic/marginally turbulent mixing. A qualitative experimental test is performed on the finalized design with mixing of 10 M urea and water to validate the flow turning unsteady mixing concept as a viable option for RNA and protein folding studies. A comparison of direct numerical simulations (DNS) and turbulence models suggests that the applicability of turbulence models to these flow regimes may be limited

The Keller-Box Scheme: A Mimetic Method that is a Bit Different

In an effort to better understand what makes a numerical method mimetic we consider an exceptional case. The Keller-Box scheme is multi-symplectic (Reich 2000), it always propagates waves in the correct direction (Frank, 2006), and it discretizes the problem physics and calculus exactly (mimetic). However, the method is not easily described by algebraic topology or discrete differential forms. The properties of this unusual mimetic method are discussed and compared to the more classical mimetic finite element and finite volume methods.Non UBCUnreviewedAuthor affiliation: University of Massachusetts, AmherstFacult

Application of the Turbulent Potential Model to Unsteady Flows and Three-Dimensional Boundary Layers

The turbulent potential model is a Reynolds-averaged (RANS) turbulence model that is theoretically capable of capturing nonequilibrium turbulent flows at a computational cost and complexity comparable to two-equation models. The ability of the turbulent potential model to predict nonequilibrium turbulent flows accurately is evaluated in this work. The flow in a spanwise-driven channel flow and over a swept bump are used to evaluate the turbulent potential model's ability to predict complex three-dimensional boundary layers. Results of turbulent vortex shedding behind a triangular and a square cylinder are also presented in order to evaluate the model's ability to predict unsteady flows. Early indications suggest that models of this type may be capable of significantly enhancing current numerical predictions of turbomachinery components at little extra computational cost or additional code complexity

Data from: How much does nasal cavity morphology matter? Patterns and rates of olfactory airflow in phyllostomid bats

The morphology of the nasal cavity in mammals with a good sense of smell includes features that are thought to improve olfactory airflow, such as a dorsal conduit that delivers odours quickly to the olfactory mucosa, an enlarged olfactory recess at the back of the airway, and a clear separation of the olfactory and respiratory regions of the nose. The link between these features and having a good sense of smell has been established by functional examinations of a handful of distantly related mammalian species. In this paper, we provide the first detailed examination of olfactory airflow in a group of closely related species that nevertheless vary in their sense of smell. We study six species of phyllostomid bats that have different airway morphologies and foraging ecologies, which have been linked to differences in olfactory ability or reliance. We hypothesize that differences in morphology correlate with differences in the patterns and rates of airflow, which in turn are consistent with dietary differences. To compare species, we make qualitative and quantitative comparisons of the patterns and rates of airflow through the olfactory region during both inhalation and exhalation across the six species. Contrary to our expectations, we find no clear differences among species in either the patterns of airflow through the airway or in rates of flow through the olfactory region. By and large, olfactory airflow seems to be conserved across species, suggesting that morphological differences appear to be driven by other mechanical demands on the snout, such as breathing and feeding. Olfactory ability may depend on other aspects of the system, such as the neurobiological processing of odours that work within the existing morphology imposed by other functional demands on the nasal cavity