Implicit large eddy simulation of the flow past NACA0012 aerofoil at a Reynolds number of 1x10^5

In this paper, the implicit Large Eddy Simulation (iLES) incorporating an unstructured 3rd-order Weighted Essential Non-Oscillatory (WENO) reconstruction method is investigated on the flow past NACA0012 aerofoil at a Reynolds number of 1 × 10^5. The flow features involve laminar separation, transition to turbulent and re-attachment. Simulations are carried out in the framework of open-source package OpenFOAM with a 2nd-order Euler implicit time integration and Pressure-Implicit Splitting-Operator (PISO) algorithm is used for the pressure-velocity coupling. Conventional LES with Wall Adapting Local Eddy Viscosity (WALE) model is also carried out as a baseline. The results are compared with Direct Numerical Simulations (DNS) under the same flow configurations. The mean quantities such as pressure coefficient and the re-attached turbulent velocity profiles are in excellent agreement with the DNS reference. On the other hand, in the transitional region, the thickness of separation bubble obtained by both iLES and LES is thinner than the DNS. The current iLES approach has achieved a 35% reduction of mesh resolution compared to wall resolving LES and 70% reduction compared to DNS, while the accuracy is mostly satisfied

Implicit and conventional large eddy simulation of flow around a circular cylinder at Reynolds number of 3900

The implicit Large Eddy Simulation (iLES) incorporating an unstructured 3rd-order Weighted Essential Non-Oscillatory (WENO) reconstruction method and the conventional Large Eddy Simulation with Wall Adapting Local Eddy-Viscosity (WALE) are investigated on the flow around a circular cylinder at a Reynolds number of 3900. Simulations are carried out in the framework of open-source package OpenFOAM with a 2nd-order Euler implicit time integration and Pressure-Implicit Splitting-Operator (PISO) algorithm is used for the pressure-velocity coupling. The results are compared to the high fidelity experiment and DNS data, and demonstrated a favourable performance for iLES with a 3rd-order WENO scheme on the instantaneous flow structure. The conventional LES on the prediction of mean surface pressure coefficient and velocity profiles on the wake can be beneficial by reducing the effect of Rhie-Chow interpolation. The spectral analysis reveals that the current simulations are also capturing Von Karman shedding frequencies and shear layer frequencies. Finally, distinct features of iLES and LES are discussed

Implicit large eddy simulations of turbulent flow around a square cylinder at Re=22,000

In this paper, the Implicit Large-Eddy Simulation (ILES) is investigated on the flow around a square cylinder incorporating an unstructured Weighted Essential Non-Oscillatory (WENO) reconstruction method for a Reynolds number of 22,000. Simulations are undertaken in the framework of open-source package OpenFOAM and additional implicit 2nd/3rd-order WENO scheme on the convective term of the viscous incompressible Navier-Stokes Equations. A 2nd-order Euler implicit time integration and Pressure-Implicit Splitting-Operator (PISO) algorithm is used to for the pressure-velocity coupling. Conventional LES with Wall Adapting Local Eddy Viscosity (WALE) model is also carried out as a baseline. The results are compared to high fidelity experiment, DNS data and conventional LES with dynamic Smagorinsky model from previous work. Results show favorable performance for ILES with 3rd-order WENO scheme compared with the conventional LES with dynamic Smagorinsky model and similar performance against LES with WALE model. Results also show acceptable predictions over time-averaged statistics with less computational effort for the ILES of 2nd-order WENO scheme. Shear layer flow analysis suggests that both ILES and LES face similar challenges with small quantities, such as shear stress. Finally, simulations are capturing Von Krmn vortex, Kelvin-Helmholtz instability and induced frequency changes

Promising photovoltaic application of multi-walled carbon nanotubes in perovskites solar cells for retarding recombination

A facile spray deposition method was developed to prepare a high-quality perovskite layer under ambient conditions. However, the performance is expected to be further improved with substrate and the hole transport layer (HTL) optimization and device structure, for instance. MWCNTs with incorporated spiro-OMeTAD exhibited J(sc) of 22.13 mA cm(-2) and PCE of 10.42%. To infer the origin of the increasing J(sc) and PCE, the optical absorption performance, charge transfer and recombination performance were investigated tau, R-ct, R-rec as a function of voltage and EIS measurements revealed the lower transfer resistance and recombination rate in PSCs with MWCNTs compared with the PSCs without MWCNTs. The increased resistance in dark conditions and the dark J-V curves explain the slight changes in the V-oc. The SEM images showed that there were no MWCNTs aggregated on the surface of the spiro/MWCNTs composite layer and part of MWCNTs was uncovered by spiro-OMeTAD at the interface of HTM and Au electrode. The decreased I-D/I-G ratio from 0.90 to 0.68 demonstrated the increased interaction between MWCNTs and spiro-OMeTAD

Fast preparation of uniform large grain size perovskite thin film in air condition via spray deposition method for high efficient planar solar cells

Spray deposition has been demonstrated to be a promising method to prepare perovskite thin film with many advantages, such as easy and processable under fully ambient condition, which is suitable for large-scale production. In this work, we reveal two typical spray deposition process of rapid and slow solvent evaporation. It is emphasized that the rapid solvent evaporation process is essential to avoid dendritic crystal and obtain dense perovskite thin film without pin-holes, which can be realized with a suitable substrate temperature. With optimized spray conditions including flow rate of precursor solution and carrier gas pressure, a dense and uniform perovskite layer with full surface coverage was immediately formed in similar to 5 s without any post-annealing process. The as-fabricated planar heterojunction solar cell achieved a power conversion efficiency (PCE) of 13.54% with 300 +/- 30 nm in thickness of perovskite layer. To the best of our knowledge, this result is the highest value for the CH3NH3PbI3 perovskite solar cells fabricated in air condition with high humidity up to 50%

Highly Solar-Reflective Litchis-Like Core-Shell HGM/TiO2 Microspheres Synthesized by Controllable Heterogeneous Precipitation Method

Hollow glass microsphere (HGM)TiO2 core-shell structural composites have promising applications in the field of energy efficient solar-reflective paints. In this work, after pretreated with saturated Ca(OH)(2) solutions, litchis-like TiO2 shells have been successfully synthesized on HGMs via a controllably heterogeneous precipitation method with Titanium (IV) sulfate (Ti(SO4)(2)) and urea as reaction precursors. It is emphasized that the use of urea as the precipitating agent is essential for the heterogeneous nucleation and growth of Ti(OH)(4) on HGMs, while the Ca(OH)(2) pretreatment provides the heterogeneous nucleation sites on HGMs which promotes the nucleation and growth of Ti(OH)(4), and gives rise to large secondary Ti(OH)(4) particles, leading to the formation of litchis-like TiO2 shells. The resulted core-shell structural HGM/TiO2 microspheres exhibited highest solar reflectance of similar to 83%

Crystal Structure Control of ZnxCd1-xS Alloyed Nanocrystals and Structural Dependent Fluorescence Properties

Crystal structure control is so important to the fluorescence properties that each element should be considered carefully. In conventional synthesis of ZnxCd1-xS alloyed nanocrystals (NCs), most of studies focus on ligand-surface interaction on the formation of either zinc blende or wurtzite ZnxCd1-xS nanocrystals, instead of the reactant source. In this work, mixed crystal phase was found easily in ZnxCd1-xS alloyed NCs when reaction proceeded at high Zn/Cd source ratio condition. Therefore, we regulate the Zn/Cd ratio to obtain relative pure zinc-blende structure, and study the influence of structure change on the fluorescence properties. Further, we have proposed a two-step ZnS coating method to acquire ZnxCd1-xS/ZnS NCs with separated crystal-phase between core and shell. Compared with maximum QY of 81% for ZnxCd1-xS/ZnS NCs synthesized by conventional one-step coating method, the performance of the optimized NCs has significantly improved with maximum QY of 93%

Stable and efficient air-processed perovskite solar cells employing low-temperature processed compact In2O3 thin films as electron transport materials

Perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies (PCEs) owing to their extraordinary optoelectronic properties. Electron transporting layer (ETL) has been proved to have a significant influence on the photovoltaic performance and stability of cell devices. Herein, for the first time, we prepare a low-temperature processed compact In2O3 film derived from a highly stable modified indium precursor solution as a promising ETL for stable and efficient air-processed PSCs. The addition of acetylacetone as a chelation ligand in the solution effectively inhibits the hydrolysis reactions by chelating In3+, thus contributing to the formation of compact In2O3 film at a low temperature of 200 degrees C. Dense CH3NH3PbI3 perovskite films with many microns-scale grains are fabricated using a scalable doctor-blade method under a harsh ambient condition (relative humidity of 40-50%). Using the proposed compact In2O3 film as ETL, the electron extraction and charge transport at the ETL/perovskite interface are significantly improved. As a result, the air-processed PSC based on compact In2O3 film delivers a champion PCE of 13.97%, greatly outperforming the device with a pristine In2O3 film (9.81%). In addition to high efficiency, the PSC incorporating proposed compact In2O3 film exhibits an excellent long-term stability, maintaining 94% of its initial PCE after stored in air for 31 days. This study demonstrates the feasibility of fabricating stable and efficient air-processed PSCs using low-temperature processed In2O3 ETL, which is expected to have a positive impact in the manufacturing community of solution-processed In2O3 film as well as air-processed PSCs. (C) 2020 Elsevier B.V. All rights reserved