Analytical and Experimental Study of the Integral Aerodynamic Characteristics of Low-Wind Turbines

This work presents experimental and analytical results for a horizontal axis wind turbine designed for operation at low wind speeds. This is dictated by the need to develop wind turbine farms at remote areas where average annual wind speeds are below 7 m/s. The key idea behind the proposed concept is the use a two-element blade. The relative position of the elements is optimized for performance. A closed-circuit, low-speed wind tunnel with open test section is used for a set of measurements on a simple wind turbine with blades made out of the CLARCK Y section without any blade twist. The experimental data is compared with results from the literature in Figure 1 [1] where the efficiency of various wind turbine types is also presented. The results suggest that good efficiencies can be obtained even at low wind speeds if the two lifting elements of the blade are positioned in an optimal way. In addition to the experimental work, an analytical method has also been developed for flapped-blades wind turbines based on the blade element momentum approach. Experimental and analytical studies suggest that the wind turbine with flapped blades design is a sound concept, and can offer a realistic alternative to conventional horizontal-axis wind turbines because of its good power efficiency at low tip speed ratios. This also means that this wind turbine has low noise level due to its lower tip speed. The proposed configuration achieves the best performance at wind speeds of 4- 7 m/s and is therefore suitable for installation at low-wind fields

Helicopter Drag Fuselage- Combined CFD and Experimental Studies

No abstract available

Microstructure and mechanical properties of a bulk ultrafine grained Al-7Si-0.3Mg alloy produced by thermomechanical consolidation of a nanocrystalline powder

A nanocrystalline Al-7Si-0.3Mg (wt%) alloy powder prepared by high energy mechanical milling was consolidated by two powder metallurgy routes to produce a bulk ultrafine grained Al-7Si-0.3Mg Alloy: vacuum hot pressing (VHP) in combination with hot extrusion (HE) and spark plasma sintering (SPS) in combination with HE. Dynamic recrystallization, Al grain growth, Si particle coarsening and formation of GP zones occurred during consolidation. Meanwhile, with increasing the extrusion ratio, the Si particles distribution became more uniform due to the flow of Si particles. With the VHP-HE route, increasing the extrusion ratio from 9:1 to 25:1 improved the tensile strength by 7.8% and elongation to fracture by 51% due to decrease of average grain size, enhancement of interparticle bonding and more uniform Si particle distribution. Similarly, with the same extrusion ratio of 9:1, the use of SPS instead of VHP for the first consolidation step did not change the tensile strength significantly, but improved the elongation to fracture by 90% for the same reasons. Analysis of the various contribution mechanisms to the yield strength shows that grain boundary strengthening and GP zone strengthening make the major contributions

Texture balancing in a fcc/bcc multilayered composite produced by accumulative roll bonding

The high strain deformation and recrystallization behaviour of a Fe/Ni multilayered composite sheet fabricated by accumulative roll bonding has been investigated. The comparable initial hardness and subsequent strain hardening behaviour of the Ni and Fe layers reduces the flow compatibility related challenges at the bonding interfaces, thereby generating parallel layers of uniform thickness during rolling to true strains up to 4.18. Typical body centred cubic (α- and γ-fibres) and face centred cubic (β-fibre) rolling textures were generated in the Fe and Ni layers, respectively. During annealing at 700 °C, recrystallization takes place homogenously in the Ni layers but commences initially by particle stimulated nucleation at oxide debris present at the interface of adjacent Fe layers. After recrystallization, the texture of the Ni layers is similar to the starting material prior to ARB, but considerable texture modification occurs in the Fe layers. For both metals, oriented growth of nucleated grains has the greatest influence on the final annealing textures, which generates the classic Cube texture in Ni and a {511} texture in Fe. While these final textures of the individual Fe and Ni layers are not conducive to good formability, texture-based Schmidt factor calculations of the combined layers show an overall balance in texture components that points to a reduction in planar anisotropy. The ability to fabricate multilayered textured sheets by this route is a promising way of controlling the anisotropy of both strength and ductility

Creep at low stresses: an evaluation of diffusion creep and Harper-Dorn creep as viable creep mechanisms

High-temperature creep experiments often reveal a transition at very low stresses to a region where the stress exponent is reduced to a value lying typically in the range of ~1 to 2. This region is generally associated with the occurrence of a new creep mechanism, such as grain-boundary sliding, diffusion creep, and/or Harper–Dorn creep. Several recent reports have suggested that diffusion creep and Harper–Dorn creep may not be viable creep mechanisms. This article examines these two processes and demonstrates that there is good evidence supporting the occurrence of both creep mechanisms under at least some experimental conditions