Numerical/experimental investigations on reducing drag penalty of passive vortex generators on a NACA 4415 airfoil

A study emphasizing the effects of passive vortex generators (VGs) on aerodynamic characteristics of a NACA 4415 airfoil is presented. Both experimental and numerical works have been carried out on an array of VGs attached to a NACA 4415 airfoil. Lift and drag measurements are made at various angles of attack by using three‐axis component balance system. On the numerical side, Reynolds‐averaged Navier‐Stokes (RANS) equations have been solved with ANSYS FLUENT 14.5 commercial code with fully structured mesh and three turbulence models (realizable k‐ε, k‐ω shear stress transport [SST] and the Spalart‐Allmaras model) at Reynolds number Re = 2 × 10⁵. Parametric studies have been conducted to find out optimal configurations with respect to span‐wise separation distance between VGs, along with their location along the chord. A very good agreement has been obtained between experimental and computational results indicating that this optimized configuration is robust for the considered parameters. It turns out that increasing the span‐wise separation length increases the aerodynamic performances (lift‐to‐drag ratio) at low attack angles for which low parasitic drag is achieved but conversely degrades it at higher ones. For the stream‐wise location along the chord, upstream position of VGs degrades the lift‐to‐drag ratio at low attack angles and conversely improves it at higher ones.     

Improvement of the heat transfer quality by air cooling of three-heated obstacles in a horizontal channel using the lattice Boltzmann method

This study focuses on the cooling of three heated obstacles with different heights mounted on the bottom of the channel wall using different aspects that influence the enhancement of the heat exchange, as is known in the concept of cooling electronic devices. The lattice Boltzmann method associated with multiple relaxation times (LBM-MRT) was adopted to simulate the physical configurations of the studied system. In this context, the D2Q9 and D2Q5 models are applied to describe the fluid flow behavior and conjugate heat transfer, respectively. The evaluation of heat exchange between the cold fluid and three-heated obstacles has been accurately analyzed under the effect of several parameters such as Reynolds number, obstacle spacing, and thermal conductivity ratio. In addition, the setting of two and three fluids flow inlets were also studied. The results are presented in terms of streamlines, isotherms, and local Nusselt curves. The heat transfer increases with increasing solid-fluid thermal conductivity. It is also more pronounced for large Reynolds numbers. Moreover, the heat transfer significantly enhances for the second and third obstacles when obstacle spacing increases. The improvement of the heat transfer is performed by the implementation of several jet flows in the studied system.     

Experimental analysis of the strength of silver–alumina junction elaborated at solid state bonding

The mechanisms of ceramics–metal assemblies, particularly silver and alumina, can be better understood by studying the strength of their adhesion. These two materials are a priori non-reactive, their thermodynamic work of adhesion is low and the difference between their thermal coefficients of expansion in very considerable. In this study, the strength of silver–alumina junctions elaborated at solid state by thermo-compression is tested by an indirect tensile test and shearing one. The effects of several parameters such as: the pressure of bonding, the time of bonding, the temperature, and the oxygen dissolve in metal solid solution on the strength of the junction are analyzed. The obtained results show that the resistance of the junction is affected by all this parameters and it is essential to optimize these different parameters in order to increase the durability of the junction. It was also shown that the diffusion of the silver in alumina could be the cause of the damage of alumina near the interface.     

Failure Analysis of Brazed Joints—A Case Study

Journal of Failure Analysis and Prevention - Heat exchangers presented water leaking at brazed joints. The first was exposed to water–salt solution, and both interfacial and crevice corrosion...     

HPLC sugar profiles of Algerian honeys

Sugar profiles of fifty honey samples from different regions of Algeria are analysed by HPLC with pulsed amperometric detection. These samples consisted of 25 multifloral and 25 unifloral honeys. Eleven sugars (two monosaccharides, nine oligosaccharides) are quantified. The mean values of fructose and glucose are in the range 35.99–42.57% and 24.63–35.06%, respectively. These monosaccharides are the main sugars of all honey samples. The sucrose, maltose, isomaltose, turanose and erlose are present nearly in all the samples, while raffinose and melezitose are detected in few samples. Furthermore, trehalose is present only in two samples and none of the samples contain melibiose. Low amounts of melezitose, raffinose and erlose are present in the range of 0.03–2.14%, 0.03–0.35% and 0.01–2.35%, respectively. PCA (Principal Component Analysis) showed that the cumulative variance was approximately 40% and Apiaceae honeys are correctly classified using FDA (Factorial Discriminant Analysis).     

Structural and elastic properties of TiN and AlN compounds: first-principles study

First-principles calculations of the lattice constants, bulk modulus, pressure derivatives of the bulk modulus and elastic constants of AlN and TiN compounds in rock-salt (B1) and wurtzite (B4) structures are presented. We have used the fullpotential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the generalized gradient approximation (GGA) for the exchange-correlation functional. Moreover, the elastic properties of cubic TiN and hexagonal AlN, including elastic constants, bulk and shear moduli are determined and compared with previous experimental and theoretical data. Our results show that the structural transition at 0 K from wurtzite to rock-salt phase occurs at 10 GPa and ?26 GPa for AlN and TiN, respectively. These results are consistent with those of other studies found in the literature.     

Implementation of Advanced Tunnel Field Effect Transistor (DP-TFET) for High Power Switching Applications

Silicon - As the technology advances to the nanoscale, advanced Tunnel Field-Effect Transistors are very prominent as a part of integrated circuits in the present trend. Advanced Tunnel FET devices...     

Rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

Properties modification by blending polymers has been an area of immense interest. In this work, rheological and mechanical properties of poly(lactic acid)/polystyrene (PLA/PS) blends were investigated. PLA/PS blends in different ratios were prepared using a laboratory scale single screw extruder to obtain (3 mm) granules. Rheological properties were studied using a capillary rheometer and the Bagley’s correction was performed. True shear rate (γ _r ), true shear stress (τ _r ), and true viscosity (η _r ) were determined, the relationship between true viscosity and (1/T) was studied for PLA70 blend and the flow activation energy at a constant shear stress (E _τ ) and a constant shear rate (E _γ ) was determined. The mechanical property measurements were performed at room temperature. Stress at break and strain at break were determined. The results showed that PLA/PS blend exhibited a typical shear-thinning behavior over the range of the studied shear rates, and the viscosity of the blend decreased with increasing PLA content. Also it was found that no equal-viscosity temperature exists between PLA and PS. The mechanical results showed immiscibility between PLA and PS in the blend.     

Brazilian disk test simulation intended for the study of interfacial cracks in bi-materials

The good mechanical characteristics of bimaterials and in particular those of the ceramic-metal couple would make them, industrially, an interesting alternative if their fracture behaviour was better understood. The difference of the mechanical properties of the bonded materials leads to a stress concentration at the vicinity of the interface. This study concerns the analysis of the interfacial fracture in Brazilian disk test, subjected to compressive load. The finite element method is used to carry out this objective. The study is limited to the case of an elastic behaviour of the two components of the assembly and to a pure junction. The behaviour of a crack located at the interface is analyzed by global approach based on the strain energy release rate. The difference of the mechanical properties of the two bonded materials leads to a mixed mode (mode I + II).