Aerodynamic design of high end wall angle turbine stages-part I: Methodology development

A design methodology is presented for turbines in an annulus with high end wall angles. Such stages occur where large radial offsets between the stage inlet and stage outlet are required, for example in the first stage of modern low pressure turbines, and are becoming more prevalent as bypass ratios increase. The turbine vanes operate within s-shaped ducts which result in meridional curvature being of a similar magnitude to the bladeto-blade curvature. Through a systematic series of idealized computational cases, the importance of two aspects of vane design are shown. First, the region of peak end wall meridional curvature is best located within the vane row. Second, the vane should be leant so as to minimize spanwise variations in surface pressure-this condition is termed "ideal lean." This design philosophy is applied to the first stage of a low pressure turbine with high end wall angles. © 2014 by ASME.

Aerodynamic design of high end wall angle turbine stages- part II: Experimental verification

An experimental investigation of a turbine stage featuring very high end wall angles is presented. The initial turbine design did not achieve a satisfactory performance and the difference between the design predictions and the test results was traced to a large separated region on the rear suction-surface. To improve the agreement between computational fluid dynamics (CFD) and experiment, it was found necessary to modify the turbulence modeling employed. The modified CFD code was then used to redesign the vane, and the changes made are described. When tested, the performance of the redesigned vane was found to have much closer agreement with the predictions than the initial vane. Finally, the flowfield and performance of the redesigned stage are compared to a similar turbine, designed to perform the same duty, which lies in an annulus of moderate end wall angles. A reduction in stage efficiency of at least 2.4% was estimated for the very high end wall angle design. © 2014 by ASME.

Double-wall carbon nanotube Q-switched and mode-locked two-micron fiber lasers

We fabricate double-wall carbon nanotube polymer composite saturable absorbers and demonstrate stable Q-switched and Mode-locked Thulium fiber lasers in a linear cavity and a ring cavity respectively. © 2011 Optical Society of America.

Fracture of brittle lattice materials: A review

The mechanics of failure for elastic-brittle lattice materials is reviewed. Closed-form expressions are summarized for fracture toughness as a function of relative density for a wide range of periodic lattices. A variety of theoretical and numerical approaches has been developed in the literature and in the main the predictions coincide for any given topology. However, there are discrepancies and the underlying reasons for these are highlighted. The role of imperfections at the cell wall level can be accounted for by Weibull analysis. Nevertheless, defects can also arise on the meso-scale in the form of misplaced joints, wavy cell walls and randomly distributed missing cell walls. These degrade the macroscopic fracture toughness of the lattice. © 2010 Springer Science+Business Media B.V.

Diameter and wall number control of carbon nanotubes by chemical vapor deposition

We analyze the relationship between the average wall number (N) and the diameter (d) for carbon nanotubes (CNTs) grown by chemical vapour deposition. It is found that N depends linearly on d for diameters in the range of 2.5-10 nm, while single wall nanotubes predominate for diameters under about 2.1 nm. The linear relationship is found to depend somewhat on the growth conditions. It is also verified that the mean diameter depends on the diameter of the originating catalyst nanoparticle, and thus on the initial catalyst thickness where a thin film catalyst is used. This simplifies the characterisation of CNTs by electron microscopy. We also find a linear relationship between nanotube diameter and initial catalyst film thickness. © 2013 AIP Publishing LLC.

A thermopile based SOI CMOS MEMS wall shear stress sensor

In this paper we present for the first time, a novel silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) MEMS thermal wall shear stress sensor based on a tungsten hot-film and three thermopiles. These devices have been fabricated using a commercial 1 μm SOI-CMOS process followed by a deep reactive ion etch (DRIE) back-etch step to create silicon oxide membranes under the hot-film for effective thermal isolation. The sensors show an excellent repeatability of electro-thermal characteristics and can be used to measure wall shear stress in both constant current anemometric as well as calorimetric modes. The sensors have been calibrated for wall shear stress measurement of air in the range of 0-0.48 Pa using a suction type, 2-D flow wind tunnel. The calibration results show that the sensors have a higher sensitivity (up to four times) in calorimetric mode compared to anemometric mode for wall shear stress lower than 0.3 Pa. © 2013 IEEE.

Controllable nanodomain defects in ferroelectric/ferroelastic biferroic thin films

Ferroelectric thin films have been intensively studied at the nanometre scale due to the application in many fields, such as non-volatile memories. Enhanced piezo-response force microscopy (E-PFM) was used to investigate the evolution of ferroelectric and ferroelastic nanodomains in a polycrystalline thin film of the simple multi-ferroic PbZr0.3Ti0.7O 3 (PZT). By applying a d.c. voltage between the atomic force microscopy (AFM) tip and the bottom substrate of the sample, we created an electric field to switch the domain orientation. Reversible switching of both ferroelectric and ferroelastic domains towards particular directions with predominantly (111) domain orientations are observed. We also showed that along with the ferroelectric/ferroelastic domain switch, there are defects that also switch. Finally, we proposed the possible explanation of this controllable defect in terms of flexoelectricity and defect pinning. © 2013 IEEE.

Interaction of a premixed flame with a liquid fuel film on a wall

© 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved. In piston engines and in gas turbines, the injection of liquid fuel often leads to the formation of a liquid film on the combustor wall. If a flame reaches this zone, undesired phenomena such as coking may occur and diminish the lifetime of the engine. Moreover, the effect of such an interaction on maximum wall heat fluxes, flame quenching, and pollutant formation is largely unknown. This paper presents a numerical study of the interaction of a premixed flame with a cold wall covered with a film of liquid fuel. Simulations show that the presence of the film leads to a very rich zone at the wall in which the flame cannot propagate. As a result, the flame wall distance remains larger with liquid fuel than it is for a dry wall, and maximum heat fluxes are smaller. The nature of the interaction of flame wall interaction with a liquid fuel is also different from the classical flame/dry wall interaction: it is controlled mainly by chemical mechanisms and not by the thermal quenching effect observed for flames interacting with dry walls: the existence of a very rich zone created above the liquid film is the main mechanism controlling quenching.

Changes in biomechanical properties of the coronary artery wall contribute to maintained contractile responses to endothelin-1 in atherosclerosis.

AIMS: Our aim was to determine whether alterations in biomechanical properties of human diseased compared to normal coronary artery contribute to changes in artery responsiveness to endothelin-1 in atherosclerosis. MAIN METHODS: Concentration-response curves were constructed to endothelin-1 in normal and diseased coronary artery. The passive mechanical properties of arteries were determined using tensile ring tests from which finite element models of passive mechanical properties of both groups were created. Finite element modelling of artery endothelin-1 responses was then performed. KEY FINDINGS: Maximum responses to endothelin-1 were significantly attenuated in diseased (27±3 mN, n=55) compared to normal (38±2 mN, n=68) artery, although this remained over 70% of control. There was no difference in potency (pD2 control=8.03±0.06; pD2 diseased=7.98±0.06). Finite element modelling of tensile ring tests resulted in hyperelastic shear modulus μ=2004±410 Pa and hardening exponent α=22.8±2.2 for normal wall and μ=2464±1075 Pa and α=38.3±6.7 for plaque tissue and distensibility of diseased vessels was decreased. Finite element modelling of active properties of both groups resulted in higher muscle contractile strain (represented by thermal reactivity) of the atherosclerotic artery model than the normal artery model. The models suggest that a change in muscle response to endothelin-1 occurs in atherosclerotic artery to increase its distensibility towards that seen in normal artery. SIGNIFICANCE: Our data suggest that an adaptation occurs in medial smooth muscle of atherosclerotic coronary artery to maintain distensibility of the vessel wall in the presence of endothelin-1. This may contribute to the vasospastic effect of locally increased endothelin-1 production that is reported in this condition.

Double-wall carbon nanotubes for wide-band, ultrafast pulse generation.

We demonstrate wide-band ultrafast optical pulse generation at 1, 1.5, and 2 μm using a single-polymer composite saturable absorber based on double-wall carbon nanotubes (DWNTs). The freestanding optical quality polymer composite is prepared from nanotubes dispersed in water with poly(vinyl alcohol) as the host matrix. The composite is then integrated into ytterbium-, erbium-, and thulium-doped fiber laser cavities. Using this single DWNT-polymer composite, we achieve 4.85 ps, 532 fs, and 1.6 ps mode-locked pulses at 1066, 1559, and 1883 nm, respectively, highlighting the potential of DWNTs for wide-band ultrafast photonics.

Widely tunable picosecond fiber ring laser mode-locked by a single-wall carbon nanotube (SWNT)-polycarbonate composite film saturable absorber

A widely tunable fiber ring laser, utilising a SWNT/polycarbonate film mode-locker and a 3-nm tunable filter, has been realized. 2.3ps pulse generation over 27nm spectral range is achieved for a constant pump power of 25mW. © 2007 Optical Society of America.