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Glasses of Sb2S3-As2S3 system with nominal composition of As0,4xSb0,4(100-x)S60 (where x= 10, 25, 50, 75 and 100 mol% As2S3) were investigated by different quenching methods and Raman spectroscopy. All studied samples were in the vitreous state. The average coordination number (Z), being equal to 2.4, has indicated that the numbers of neighbors of non-chalcogens (As and Sb) and chalcogens (S and Te) atoms were respectively 3 and 2. These coordination numbers were conditions fulfilled by the atoms to obtain vitreous materials. The vibrations of the SbS3 and AsS3 structural units dominated the Raman spectra of the studied Sb2S3-As2S3 glasses. [ABSTRACT FROM AUTHOR]

This paper presents a joint experimental and computational study of the effect of the bluff-body diameter on the flow field and residence time distribution (RTD) in a set of turbulent non-premixed ethylene/nitrogen flames with a high soot load. A novel optical design has been developed to undertake the PIV measurements successfully in highly-sooting turbulent flames, using polarizing filters. The mean velocity components and turbulent intensity are reported for three bluff-body burners with different bluff-body diameters (38, 50, and 64 mm), but which are otherwise identical in all other dimensions. The central jet diameter of 4.6 mm was supplied with a mixture of ethylene and nitrogen (4:1, by volume) to achieve a bulk Reynolds number of 15,000 for the reacting cases. Isothermal cases were also investigated to isolate the effect of heat release on the flow fiel. Pure nitrogen was utilized in the isothermal cases where the Reynolds number was kept the same as the reacting cases. The annular bulk velocity of the co-flowing air was kept constant at 20 m/s for all experiments. Computationally, a 2-D RANS model was developed, validated against the experimental data and was mainly used to investigate the effect of the bluff body diameter on the residence time in the recirculation zone. The flow structure for both isothermal and reacting cases was found to be consistent with the literature, exhibiting similar vortical structures of the recirculating zone and mixture fraction distribution, for similar momentum flux ratios. The flame length and volume were found to decrease by 20% and 9%, respectively, as the bluff diameter was increased from 38mm to 64mm. The length of the recirculation zone for the isothermal cases was found to be ~1.2DBB, while for the reacting cases it was ~1.5–1.75DBB. A stochastic tracking model was employed to estimate the pseudo-particles' residence time distribution in the recirculation region. The model revealed that an increase in the bluff body diameter from 38mm to 64 mm leads to tripling of the mean residence time within the recirculation zone. Thermal radiation measurements from the recirculation zone show a 35% increase as the bluff body diameter is increased from 38 mm to 64 mm, whilst the total radiation from the whole flame drops by 15%, which is deduced to be due mostly to the decrease in flame volume. The effect of these differences on soot propensity and transport are described briefly and will be the subject of future investigations. [ABSTRACT FROM AUTHOR]

Glasses of binary systems (Sb2S3-As2S3 and Sb2Te3-As2S3) and ternary sections (containing 10, 20 and 40 mol% of Sb2Te3) belonging to Sb2S3-As2S3-Sb2Te3 system were prepared by rapid quenching method in ice water of their liquid phases. From chemical formulas obtained by using Energy Dispersion Spectroscopy (EDS), average values of Sb2S3-As2S3-Sb2Te3 glasses' parameters such as coordination number (Z), atomic radius (Rav), atomic number (Zav), atomic molar mass (Mav) and electronegativity (Xav) were calculated. These parameters were used to explain the formation of the glasses in the Sb2S3-As2S3-Sb2Te3 system by following their evolution as a function of the As2S3 content. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental campaign to measure thruster-relevant parameters for a high-power (180kW) inductive propulsion system utilising Ar, $ {\textrm{O}}_{2}$ , $ \textrm{N}_{2}$ , and $ \textrm{CO}_{2}$ as propellants. Results from the investigation show that inductive thrusters can make use of these propellants without the severe degradation seen in other electric propulsion systems. Furthermore, the collection of experimental data at powers greater than 100kW provides a reference of performance for the high-power electric propulsion devices intended for missions in the near future. Thrust and specific impulse in inductive systems can be improved by preferentially combining the chemical properties of atomic and molecular propellants. The maximum thrust recorded during these experiments was 7.9N, obtained using a combination of argon and oxygen (0.68 Ar + 0.32 $\textrm{O}_{2}$). The combination of argon and molecular propellants also decreased thermal losses within the discharge volume. Specific impulse can be doubled for the same input electric power by combining propellants, and future modifications to the thruster geometry and acceleration mechanism can be used to further improve the performance of such systems. [ABSTRACT FROM AUTHOR]

Electromagnetic plasma generators (inductive and helicon) are commonly used for planetary entry simulation and increasingly for electric propulsion applications. However, one obstacle in increasing the power and efficiency of these systems is a lack of knowledge regarding the distribution of tube wall temperature. The tube wall temperature acts as a mechanical limit to the thruster/generator operating conditions and is directly related to the distribution of thermal energy within the discharge volume. This paper presents the results of an experimental investigation to determine spatially resolved wall temperatures in a 180 kW inductive plasma generator. This investigation showed that significant wall heating does not occur until the midpoint of the inductive coil, increasing rapidly to reach peak temperature over a distance 15% of the total tube. During this rapid heating phase, one-third of the total tube heat flux is produced, assisting in quantifying previously observed mechanical failures due to thermal stress. The peak temperature difference between inner and outer wall surfaces was recorded as 619.1 K, approximately twice that of the previously proposed limit which considered integral rather than spatially resolved values. Using the results of this investigation, a refined estimate of critical wall temperatures for various tube thicknesses has been developed, allowing more targeted cooling systems to be implemented in the future generator designs. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the effects of multilateral jet mixing, using both three and four side-jets, on the structure and stability of turbulent partially-premixed flames. Particle Image Velocimetry and OH*-chemiluminescence were used to study the effects of geometry and operating conditions on the resulting flow-field and reaction zone structures, respectively. These effects were compared under varying ratios of side-jet to primary flow momentum, whilst keeping the bulk flow constant. It was found that the mixing regimes upstream of the nozzle exit affect the flame characteristics, i.e. an impinging regime is likely to generate a lifted flame whilst a backflow regime is likely to generate an attached flame. Unlike the 4 side-jets cases, the OH* images and v profiles for the 3 side-jets cases show distinct asymmetry, with intense OH* and low velocity fluctuations on the opposite sides of the fuel injection. It was also found that the flow and scalar fields become independent of the upstream conditions, for both 3 and 4 side-jets, after one diameter downstream of the nozzle exit. [ABSTRACT FROM AUTHOR]

Wings with tubercles have been shown to display advantageous loading behavior at high attack angles compared to their unmodified counterparts. In an earlier study by the authors, it was shown that an undulating leading-edge configuration, including but not limited to a tubercled model, induces a cyclic variation in circulation along the span that gives rise to the formation of counter-rotating streamwise vortices. While the aerodynamic benefits of full-span tubercled wings have been associated with the presence of such vortices, their formation mechanism and influence on wing performance are still in question. In the present work, experimental and numerical tests were conducted to further investigate the effect of tubercles on the flow structure over full-span modified wings based on the NACA 0021 profile, in the transitional flow regime. It is found that a skew-induced mechanism accounts for the formation of streamwise vortices whose development is accompanied by flow separation in delta-shaped regions near the trailing edge. The presence of vortices is detrimental to the performance of full-span wings pre-stall, however renders benefits post-stall as demonstrated by wind tunnel pressure measurement tests. Finally, primary and secondary vortices are identified post-stall that produce an enhanced momentum transfer effect that reduces flow separation, thus increasing the generated amount of lift. [ABSTRACT FROM AUTHOR]

In spite of its mammoth physical size, the humpback whale's manoeuvrability in hunting has captured the attention of biologists as well as fluid mechanists. It has now been established that the protrusions on the leading-edges of the humpback's pectoral flippers, known as tubercles, account for this species' agility and manoeuvrability. In the present work, Prandtl's nonlinear lifting-line theory was employed to propose a hypothesis that the favourable traits observed in the performance of tubercled lifting bodies are not exclusive to this form of leading-edge configuration. Accordingly, a novel alternative to tubercles was introduced and incorporated into the design of four airfoils that underwent wind tunnel force and pressure measurement tests in the transitional flow regime. In addition, a Computation Fluid Dynamics study was performed using the Shear Stress Transport transitional model in the context of unsteady Reynolds-Averaged Navier-Stokes at several attack angles. The results from the numerical investigation are in reasonable agreement with those of the experiments, and suggest the presence of features that are also observed in flows over tubercled foils, most notably a distinct pair of streamwise vortices for each wavelength of the tubercle-like feature. [ABSTRACT FROM AUTHOR]