AN UNFACTORED IMPLICIT MOVING MESH METHOD FOR THE TWO-DIMENSIONAL UNSTEADY N–S EQUATIONS

An unfactored implicit time-marching method for the solution of the unsteady two-dimensional Reynolds-averaged thin layer Navier–Stokes equations is presented. The linear system arising from each implicit step is solved by the conjugate gradient squared (CGS) method with preconditioning based on an ADI factorization. The time-marching procedure has been used with a fast transfinite interpolation method to regenerate the mesh at each time step in response to the motion of the aerofoil. The main test cases examined are from the AGARD aeroelastic configurations and involve aerofoils oscillating rigidly in pitch. These test cases have been used to investigate the effect of various parameters, such as CGS tolerance and laminar/turbulent transition location, on the accuracy and efficiency of the method. Comparisons with available experimental data have been made for these cases. In order to illustrate the application of the mesh generator and flow solver to more general flows where the aerofoil deforms, results for an NACA 0012 aerofoil with an oscillating trailing edge flap are also shown.     

基于Hopf-Cole变换的Burgers方程初边值问题的Sinc-Galerkin法

利用Sinc-Galerkin法数值求解Burgers方程的初边值问题。首先,用Hopf-Cole变换将二阶非线性的Burgers方程变换为二阶线性方程,同时把第一类边界条件变为第二类边界条件。时间上的导数采用θ加权格式离散,空间导数采用Sinc-Galerkin法离散,端点处分别引入权函数处理变换后的第二类边界条件。最后,通过数值算例验证了Sinc-Galerkin法的指数收敛性,与精确解相比,本文构造的数值格式精度高,能够有效捕捉激波等物理现象。     

Numerical and Experimental Investigation of the Conjugate Heat Transfer for a High-Pressure Pneumatic Control Valve Assembly

This paper uses heat transfer experiments and computational fluid dynamics (CFD) simulations to investigate the conjugate heat transfer (CHT) in a high-pressure pneumatic control valve assembly. A heat transfer test rig was constructed, and time–temperature histories of five test points placed on the valve assembly’s outer surface were recorded for study validation. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) CFD methods with the standard k-ε turbulence closure equations were adopted in the numerical computations. Polyhedral grids were used; time step and mesh convergence studies were conducted. Simulated and measured temperatures profile comparisons revealed a good agreement. The CHT results obtained from CFD showed huge velocity fields downstream of the valve throat and the vent hole. The airflow through the valve was icy, mainly in the supersonic flow areas. Low temperatures below 273.15 K were recorded on the internal and external walls of the valve assembly. The consistency of the measured data with the numerical results demonstrates the effectiveness of polyhedral grids in exploring the CHT using CFD methods. The local entropy production rate analysis revealed that irreversibility is mainly due to viscous dissipation. The current CHT investigation provides a potential basis for thermostress analysis and optimization.     

Thermal stability of Li2O-SiO2-CaO-P2O5-F glass

Two glasses, the first one with the composition of Li₂O·2SiO₂ and the second one with the addition of CaO, P₂O₅ and CaF₂ in the stoichiometric ratio corresponding to fluoroapatite were prepared and their tendency to crystallize has been studied by non-isothermal DTA analysis. The values of kinetic parameters calculated using the isoconversional integral method have been used to determine the temperature dependencies of both the length of isothermal induction period and the length of overall isothermal crystallization for both glasses. The estimated dependencies indicate that the glass containing CaO, P₂O₅ and CaF₂ has a lower thermal stability.     

Magnetic microsphere-based methods to study the interaction of teicoplanin with peptides and bacteria

Teicoplanin (teic) from Actinoplanes teichomyceticus is a glycopeptide antibiotic used to treat many Gram-positive bacterial infections. Glycopeptide antibiotics inhibit bacterial growth by binding to carboxy-terminal d-Ala-d-Ala intermediates in the peptidoglycan of the cell wall of Gram-positive bacteria. In this paper we report the derivatization of magnetic microspheres with teic (teic-microspheres). Fluorescence-based techniques have been developed to analyze the binding properties of the microspheres to two d-Ala-d-Ala terminus peptides. The dissociation constant for the binding of carboxyfluorescein-labeled d-Ala-d-Ala-d-Ala to teic on microspheres was established via fluorimetry and flow cytometry and was determined to be 0.5 × 10⁻⁶ and 3.0 × 10⁻⁶ mol L⁻¹, respectively. The feasibility of utilizing microparticles with fluorescence methods to detect low levels (the limit of bacterial detection was determined to be 30 colon-forming units; cfu) of Gram-positive bacteria has been demonstrated. A simple microfluidic experiment is reported to demonstrate the possibility of developing microsphere-based affinity assays to study peptide–antibiotic interaction.     

Selective Synthesis of 2,5‐Diformylfuran by Sustainable 4‐acetamido‐TEMPO/Halogen‐Mediated Electrooxidation of 5‐Hydroxymethylfurfural

A new method was developed for the selective gram‐scale synthesis of 2,5‐diformylfuran (DFF), which is an important chemical with a high application potential, via oxidation of biomass‐derived 5‐hydroxylmethylfurfural (HMF) catalyzed by 4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (4‐AcNH‐TEMPO) in a two‐phase system consisting of a methylene chloride and aqueous solution containing sodium hydrogen carbonate and potassium iodide. The key feature of this method is the generation of the I₂ (co‐)oxidant by anodic oxidation of iodide anions during pulse electrolysis. In addition, the electrolyte can be successfully recycled five times while maintaining a 62–65 % yield of DFF. This novel method provides a sustainable pathway for waste‐free production of DFF without the use of metal catalysts and expensive oxidants. An advantage of electrooxidation is utilized in the preparation of demanding chemical.     

Recovery-Based Error Estimator for Natural Convection Equations Based on Defect-Correction Methods

In this paper, we propose an adaptive defect-correction method for natural convection (NC) equations. A defect-correction method (DCM) is proposed for solving NC equations to overcome the convection dominance problem caused by a high Rayleigh number. To solve the large amount of computation and the discontinuity of the gradient of the numerical solution, we combine a new recovery-type posteriori estimator in view of the gradient recovery and superconvergent theory. The presented reliability and efficiency analysis shows that the true error can be effectively bounded by the recovery-based error estimator. Finally, the stability, accuracy and efficiency of the proposed method are confirmed by several numerical investigations.