Response of dispersed droplets to shock waves in supersonic mixing layers

The response of dispersed droplets to oblique shock waves in the supersonic mixing layer was investigated using the large eddy simulation coupled with the particle Lagrangian tracking model. The generated disturbances based on the most-unstable wave model were imposed to excite the development of supersonic shear layer. The oblique shock wave was numerically introduced in the flow field. Small- and medium-sized droplets remained their preferential distribution in the vortices after crossing the shock wave, while large-sized droplet became more dispersed. The influence of shock waves on the momentum and heat transfers from surrounding gas to droplets was analyzed by tracking droplets’ motion paths. Small-sized droplets responded easily to the shock wave. Compared with the aerodynamic response, the thermal response of droplets was slower, especially under the impaction of the shock wave. The present research conclusions are conductive to analyze the mixing of air and fuel droplets and of important academic value for further understanding the two-phase dynamics in combustors of scramjet

Stochastic separated flow models with applications in numerical computations of supersonic particle-laden turbulent flows

In this article, three stochastic separated flow models were applied to predict the dispersion of inertial fuel particles in the supersonic turbulent flows. The flow field of continuous phase was simulated by means of Reynolds-averaged Navier–Stokes method with a two-equation turbulence model. Clift’s expression was used to modify the drag force on the particle considering the compressibility effects. The particle-phase statistics were obtained by a secondary-order time-weighed Eulerian method. The ability of those stochastic separated flow models was then compared for predicting the mean particle velocity and the particle dispersion. For obtaining a statistically stationary solution, the stochastic separated flow model required the largest number of computational particles, whereas the improved stochastic separated flow model was found to need the least. The time-series stochastic separation flow model lay in-between. Compared with the other two models, the particle dispersion was over-predicted by the stochastic separated flow model in the supersonic particle-laden boundary layer flow, while the improved stochastic separated flow model was less predictable for the particle spatial distribution in the particle-laden strut-injection flow. Three models could well predict the mean velocities of the particle phase. This study is valuable for selecting a validated model used for predicting the particle dispersion in supersonic turbulent flows

Co3+-O-V4+ cluster in CoVOx nanorods for efficient and stable electrochemical oxygen evolution

The development of cost-efficient and long-term stable catalysts for the oxygen evolution reaction (OER) is crucial to produce clean and sustainable H2 fuels from water. Here we demonstrate a cobalt vanadium oxide (CoVOx-300) working as such an efficient and durable electrocatalyst. Such an active catalyst is beneficial from the balanced Co3+-O-V4+ active species, which show the high surface Co3+ contents with matched V4+ generated by rapid heat treatment. The CoVOx-300 with highest Co3+/Co2+ ratio of 1.4 and corresponding highest V4+/ V5+ ratio of 1.7 exhibits remarkable OER activity with an overpotential of 330 mV at current density of 10 mA cm−2 (η10), a shallow Tafel slope of only 46 mV dec-1 and a current density of 100 mA cm−2 at an overpotential of 0.38 V vs RHE, which is 20 times higher than the active CoOx-300 and 1000 times higher than VOx-300. The catalyst also shows excellent stability for 10 h in alkaline media and a 40 % reduced activation energy to the counterpart, CoOx-300. The overpotential (η10) of CoVOx-300 also shows nearly 70 and 80 mV lower than the corresponding CoOx-300 and CoVOx catalysts, respectively and 20 % lower Tafel slope than the commercial benchmark catalyst RuO2. Thus, this study for the first time demonstrates that surface Co3+-O-V4+ species play a crucial role in improving electrocatalytic properties and stability for water oxidation reaction and the approaches allow the rational design and synthesis of other active transition metal oxides toward efficient OER activity

Phylogeny of the Infraorder Pentatomomorpha Based on Fossil and Extant Morphology, with Description of a New Fossil Family from China

<div><h3>Background</h3><p>An extinct new family of Pentatomomorpha, Venicoridae Yao, Ren & Cai <b>fam. nov.</b>, with 2 new genera and 2 new species (<em>Venicoris solaris</em> Yao, Ren & Rider <b>gen. & sp. nov.</b> and <em>Clavaticoris zhengi</em> Yao, Ren & Cai <b>gen. & sp. nov.</b>) are described from the Early Cretaceous Yixian Formation in Northeast China.</p> <h3>Methodology/Principal Findings</h3><p>A cladistic analysis based on a combination of fossil and extant morphological characters clarified the phylogenetic status of the new family and has allowed the reconstruction of intersuperfamily and interfamily relationships within the Infraorder Pentatomomorpha. The fossil record and diversity of Pentatomomorpha during the Mesozoic is discussed.</p> <h3>Conclusions/Significance</h3><p>Pentatomomorpha is a monophyletic group; Aradoidea and the Trichophora are sister groups; these fossils belong to new family, treated as the sister group of remainder of Trichophora; Pentatomoidea is a monophyletic group; Piesmatidae should be separated as a superfamily, Piesmatoidea. Origin time of Pentatomomorpha should be tracked back to the Middle or Early Triassic.</p> </div