Numerical study of longitudinal vein effects on the aerodynamic characteristics of a corrugated bio-airfoil

The purpose of the present study is to investigate the influence of cross-sectional veins topology on the flow pattern and aerodynamic performance of a pitching corrugated bio-inspired airfoil. To demonstrate the vein effects, a cross-section of Ashena Cyanea wing is modelled with three configurations. The airflow passing bio-airfoil is subjected to three Reynolds numbers of 1000, 5000, and 14000 and selected reduced frequencies () and angular amplitude (). The results show that as the Reynolds number increases, the effects of veins structure become more significant. The lift coefficients of the three modelled bio-airfoils are almost identical over the range of selected Reynolds number. At the Reynolds numbers of 1000 and 5000, the thin bio-airfoil has a minimum drag coefficient, and the drag coefficients of thick and veined bio-airfoils are quite similar. The veins in the bio-airfoils increase the drag coefficient significantly for the Reynolds numbers of 14000 compared to the Reynolds number of 5000. Finally, the numerical simulations provide hysteresis of lift and drag coefficients subjected to an increment for Reynolds number, reduced frequency, and angular amplitude

A numerical investigation of CO2 dilution on the thermochemical characteristics of a swirl stabilized diffusion flame

The turbulent combustion flow modeling is performed to study the effects of CO2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approach along with three well-known turbulence models is utilized to model the turbulent combustion flow field. The k-ω shear stress transport (SST) model shows the best agreement with the experimental measurements compared with other models. Therefore, the k-ω SST model is used to study the effects of CO2 dilution on the flame structure and strength, temperature distribution, and CO concentration. To determine the chemical effects of CO2 dilution, a fictitious species is replaced with the regular CO2 in both the fuel stream and the oxidizer stream. The results indicate that the flame temperature decreases when CO2 is added to either the fuel or the oxidizer stream. The flame length reduction is observed at all levels of CO2 dilution. The H radical concentration indicating the flame strength decreases, following by the thermochemical effects of CO2 dilution processes. In comparison with the fictitious species dilution, the chemical effects of CO2 addition enhance the CO mass fraction. The numerical simulations show that when the dilution level is higher, the rate of the flame length reduction is more significant at low swirl numbers

Large eddy simulation of separated flow to investigate heat transfer characteristics in an asymmetric diffuser subjected to constant wall heat flux

In the present study, heat transfer characteristics of an asymmetric diffuser with separated flow has been studied. The flow separation is triggered due to wall expansion in two directions. Large Eddy Simulation (LES) approach is adopted to solve the turbulent separated flow and heat transfer in such diffuser at Reynolds number of 10000. For this purpose, a finite volume solver is extended in the OpenFOAM framework to solve the energy equation for incompressible flow. The extended solver has been adjusted to deal with backscatter phenomena and to prevent non-physical heat transfer results and numerical instability. An appropriate grid resolution is employed to perform LES calculations and predict the characteristics of the heat transfer within the separated flow. The numerical results are validated against measurements and Direct Numerical Simulation (DNS) results. The present study showed that the low mean velocity and turbulent kinetic energy (TKE) in a separated flow region are responsible for generating high temperature hot spots resulted from significant reduction of heat transfer from the walls. It has been observed that the heat transfer from the wall is increased slightly before the flow re-attachment region. The applicability of the Reynolds analogy in the separated flow zone for this problem has been examined. Moreover, the analysis of the computational performance showed that increasing the number of computational cells can improve, to certain extent, the convergence rate of the solver and therefor, reduced the computation cost

Highly Efficient Pure-Blue Perovskite Light-Emitting Diode Leveraging CsPbBrxCl3-x/Cs4PbBrxCl6-x Nanocomposite Emissive Layer with Shallow Valence Band

Metal-halide perovskite light-emitting diodes (PeLEDs) have shown great advancement in green, red, and near-infrared regions with external quantum efficiencies (EQEs) exceeding 20%. However, blue PeLEDs, an essential part of displays and lightings, show limited progress compared to the other color counterparts. Herein, a highly efficient pure-blue PeLED is demonstrated by leveraging a novel CsPbBrxCl3-x/Cs4PbBrxCl6-x nanocomposite perovskite film as an emissive layer. The Cs4PbBrxCl6-x phase, the derived phase of CsPbBr3 perovskite with a mixed halide system, effectively passivates defects in CsPbBrxCl3-x, leading to high luminescence efficiency due to the significant reduction of nonradiative recombination. Furthermore, experimental and computational results confirmed that the compositionally optimized nanocomposite layer possesses a shallower valence band maximum (approximate to 5.5 eV) than the pristine perovskite layer (approximate to 5.9 eV), which is very advantageous in hole injection for device operation. The combined effects of the CsPbBrxCl3-x/Cs4PbBrxCl6-x nanocomposite render the fabricated blue PeLED to exhibit a pure-blue emission at 470 nm with a maximum EQE of 5.3%

Frugal discrete memristive device based on potassium permanganate solution

Many thin film-based devices with solid electrolytes have been studied for memristive applications. Herein, we report a simple and facile way to fabricate solution-based, low-cost, and discrete two-terminal memristive devices using the KMnO4 solution. The water and methanol were used as a solvent to prepare different concentrations of KMnO4 to carry out the optimization study. Furthermore, the effect of KMnO4 concentration with aqueous and methanol solvents was studied with the help of current-voltage, device charge, charge-flux, and cyclic endurance properties. Interestingly, all developed devices show the asymmetric time-domain charge and double valued charge-flux properties, suggesting that aqueous KMnO4 and methanol-KMnO4 based devices are non-ideal memristors or memristive devices. The statistical measures such as cumulative probability and coefficient of variation are reported for the memristive devices. The possible switching mechanism of the discrete memristive was tried to explain with the UV-visible spectrum and theoretical framework. The optimized device was further studied using the cyclic voltammogram, Bode plot, and Nyquist plot. An equivalent circuit was derived for the optimized discrete memristive device using electrochemical impendence spectroscopy results. The results of the present investigation are beneficial to develop programmable analog circuits, volatile memory, and synaptic devices using discrete memristive devices

Capacitive coupled non-zero I-V and type-II memristive properties of the NiFe2O4-TiO2 nanocomposite

In the present work, we have demonstrated the capacitive coupled non-zero and type-II hysteresis behavior of nickel ferrite (NFO)-titanium oxide (TiO2) nanocomposite. For this, NFO nanoparticles (NPs) and TiO2 NPs were synthesized using hydrothermal and sol-gel method, respectively. The NFO-TiO2 nanocomposite was prepared using a solid-state reaction method and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscope, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The electrical results of the NFO-TiO2 memory device have shown non-zero I-V (unable to cross at origin), cross-over I-V and type-II hysteresis (tangential hysteresis loops) properties and their occurrence was depended upon the magnitude of the electrical stimulus. To further clarify the dominance of the memristive and type-II properties, we have calculated the charge-flux and non-transversal di/dv(t) characteristics of the device based on experimental results. The charge transport mechanisms were investigated and a plausible resistive switching mechanism was reported. Our investigations provide some insights to explain the non-zero and type-II hysteresis behavior of the memristive devices