We propose a computationally tractable model for film formation and breakup based on data from experiments and direct numerical simulations. This work is a natural continuation of previous studies where primary atomization is modeled based on local flow information from a relatively low-resolution tracking of the liquid interface [1]. Sub-models for film formation are supported by direct numerical simulations obtained with the Refined Level Set Grid (RLSG) method [2]. The overall approach is validated by a carefully designed experiment [3], where the liquid jet is cross flow-atomized in a rectangular channel so that a film forms on the wall opposite to the injection orifice. The film eventually breaks up at the downstream exit of the channel. Comparisons with Phase Doppler Particle Analyzer (PDPA) data and with non-intrusive film thickness point measurements complete this study.
Single substances within complex vertebrate chemical signals could be physiologically or behaviourally active. However, the vast diversity in chemical structure, physical properties and molecular size of semiochemicals makes identifying pheromonally active compounds no easy task. Here, we identified two volatile cyclic dipeptides, cyclo(L-Leu-L-Pro) and cyclo(L-Pro-L-Pro), from the complex mixture of a chemical signal in terrestrial vertebrates (lizard genus Sceloporus), synthesised one of them and investigated their biological activity in male intra-specific communication. In a series of behavioural trials, lizards performed more chemosensory behaviour (tongue flicks, lip smacks and substrate lickings) when presented with the synthesised cyclo(L-Pro-L-Pro) chemical blend, compared to the controls, the cyclo(L-Leu-L-Pro) blend, or a combined blend with both cyclic dipeptides. The results suggest a potential semiochemical role of cyclo(L-Pro-L-Pro) and a modulating effect of cyclo(L-Leu-L-Pro) that may depend on the relative concentration of both compounds in the chemical signal. In addition, our results stress how minor compounds in complex mixtures can produce a meaningful behavioural response, how small differences in structural design are crucial for biological activity, and highlight the need for more studies to determine the complete functional landscape of biologically relevant compounds. Chemical signals of terrestrial vertebrates tend to be complex mixtures of compounds 1. However, this does not necessarily mean that numerous compounds are always needed for recognition by a signal receiver (e.g. 2-4). Single compounds, or even a selected profile from all mixture components, could be physiologically or behaviourally active in different contexts 5-8. Intra-specific chemical signals, often liberally referred to as "pheromones" in the extensive literature, can vary considerably in their chemical structure, physical properties and molecular size 9 , and there is currently no simple way to rule out the biological roles of additional mixture components. For example, even in an extensively studied model system such as the house mouse, the biological roles of volatile ligands, compared to the lipocalin proteins that are involved in different chemosensory functions 10-13 , are relatively unknown. Using an interdisciplinary approach, here we characterise two volatile cyclic dipeptides from the complex mixture of a chemical signal in terrestrial vertebrates (lizard genus Sceloporus) and investigate their biological activity in intra-specific communication. The structural diversity of compounds documented in terrestrial vertebrates is enormous 14 , and it has been difficult to associate specific structural designs or features with chemical signalling in general 1. It has been somewhat useful to divide potential chemosignals according to their volatility: while volatile pheromones can act in longer distance signalling, protein-like molecules and other highly polar substances with very low vapour pressure (e.g. polypept...
Practical aero-engine fuel injection systems are highly complicated, combining complex fuel atomizer and air swirling elements to achieve good fuel-air mixing as well as long residence time in order to enhance both combustion efficiency and stability. While detailed understanding of the multiphase flow processes occurring in a realistic injector has been limited due to the complex geometries and the challenges in near-field measurements, high fidelity, first principles simulation offers, for the first time, the potential for a comprehensive physics-based understanding. In this work, such simulations have been performed to investigate the spray atomization and subsequent droplet transport in a swirling air stream generated by a complex multi-nozzle/swirler combination. A Coupled Level Set and Volume Of Fluid (CLSVOF) approach is used to directly capture the liquid-gas interface and an embedded boundary (EB) method is applied to flexibly handle the complex injector geometry. The ghost fluid (GF) method is also used to facilitate simulations at realistic fuel-air density ratio. Adaptive mesh refinement (AMR) and Lagrangian droplet models are used to efficiently resolve the multi-scale processes. To alleviate the global constraint on the time-step imposed by locally activated AMR near liquid jets, a separate AMR simulation focusing on jet atomization was performed for relatively short physical time and the resulting Lagrangian droplets are coupled into another simulation on a uniform grid at larger time-steps. The high cost simulations were performed at the U.S. Department of Defense high performance computing facilities using over 5000 processors. Experiments at the same flow conditions were conducted at UTRC. The simulation details of flow velocity and vorticity due to the interaction of the fuel jet and swirling air are presented. The velocity magnitude is compared with experimental measurement at two downstream planes. The two-phase spray spreading is compared with experimental images and the flow details are further analyzed to enhance understanding of the complex physics.
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