Developing and testing a novel pressure-controlled hydraulic profile for siphon-shaft spillways

The operating heads of the siphon-shaft spillways are limited by cavitational pressure due to low siphonic pressure inside the spillway shaft. Therefore, these low pressures inside the shaft must be eliminated to control the cavitation. An innovative idea is to enlarge the shaft cross-section upwards where siphonic pressure decreases. For this purpose, in this study, a new pressure-controlled siphon-shaft profile was developed analytically based on Bernoulli principle and cavitational pressure. The hydraulic performance of the profile is numerically tested by means of computational fluid dynamics (CFD). The numerical model used was validated with the results of a benchmark model, and the discretization errors were estimated based on a procedure recommended by American Society of Mechanical Engineers (ASME). The verified models used to analyze the novel hydraulic design together with the classical Wagner profile originally applied to shaft/morning glory spillways. The analysis results indicated that the pressure-controlled siphon-shaft profile is quite effective in terms of cavitation protection and hydraulics performance for siphon-shaft spillways.     

Effect of anti-vortex structures installed on stepped labyrinth side weirs on discharge capacity

Side weirs are essential structural elements commonly used to control water levels in rivers and canals. If the length of the opening is limited, a labyrinth side weir can be used to increase the amount of water diverted out of the channel and the effective length. This research studied the influence of installing an antivortex structure in stepped labyrinth side weirs on discharge capacity. It has four types of antivortex installed in different hydraulic conditions at different Froude numbers, dimensionless crest height, dimensionless weir opening length, step number, and head angle. Using data from 168 experimental runs without antivortex to allow comparison and 672 experimental runs to determine the best performance of antivortex structures that improved discharge capacity, and 528 runs measured velocity to investigate the intensity of secondary currents generated by lateral flow and other hydraulic conditions, including water surface profiles. According to the research results, installing antivortices regulated the flow, significantly improved the efficiency of the single-cycle stepped labyrinth side weir, and lowered secondary flows caused by interaction with the vertical axis. Finally, the discharge coefficient improves to 18% after analyzing the best type of antivortex, considering shape and height.     

Optical counting of guided particles in a vortex beam as an optical tube by laser-two-focus method

In this study, microscopic particles such as aerosols were counted by Laser-Two-Focus method, L2F, after being trapped and guided by an optical tube. This prevents particles diffusivity as they pass through the Gaussian beam in the L2F method by optical forces such as radiation pressure and photophoretic forces. In optical tube, particles can guid to the center of the beam where the intensity gets zero. A single-charged Bessel Gaussian beam, BG₀₁, is used as the particle guidance beam in this method, which is generated by passing the first-order Laguerre-Gaussian beam, LG₀₁, from an axicon lens. LG₀₁ beam are also produced by using holographic interference grid mask. The results of the theory and simulations showed that by optical guiding of particles in the L2F-method measurement, their transverse turbulence can be reduced by about 60% and then the probability of measuring all particles to be increased by about 30%. Measurements of in-laboratory aerosols less than 3.5 μm with this method showed a 20% increase in their condensation of them compared to the conventional L2F method.     

Current challenges and potential directions towards precision microscale additive manufacturing – Part IV: Future perspectives

Microscale additive manufacturing is one of the fastest growing areas of research within the additive manufacturing community. However, there are still significant challenges that exist in terms of available materials, resolution, throughput, and ability to fabricate true three-dimensional geometries. These challenges render commercialization of currently available microscale additive manufacturing processes difficult. This paper is the last one in a four-part series of articles which review the current state-of-the-art of microscale additive manufacturing technologies and investigate the factors that currently limit each microscale additive manufacturing technology in terms of materials, resolution, throughput, and ability to fabricate complex geometries. Parts I, II and III offer prognoses about the future viability and applications of each technology along with suggested future research directions that could be used to bring each process technology in line with its fundamental, physics-based limitations. This paper brings together the general design guidelines that must be followed while designing scalable microscale AM processes. Finally, the paper concludes with an analysis of the role of precision engineering in the future advancement of microscale additive manufacturing technologies. This series of publications is a joint effort by the members and affiliates of the Micro-Nano Technical Leadership Committee of the American Society for Precision Engineering (ASPE).     

On air entrapment onset and surface velocity in high-speed turbulent prototype flows

In a free-surface spillway, the upstream flow is non-aerated and the flow becomes a strong air-water mix downstream of the onset location of air entrapment. Field observations were conducted over a steep spillway chute, and detailed quantitative measurements were undertaken in real-world high-speed flows with strong turbulence and very high Reynolds numbers within the range 10⁷ to 10⁸. The data showed that the onset of air entrapment is a complicated transient three-dimensional process in high-speed strongly-turbulent flows. A robust optical flow (OF) technique was applied and provided physically-meaningful surface velocities in the non-aerated flow region. The streamwise velocities were reasonably close to ideal fluid flow calculations, with large streamwise surface velocity fluctuations, in the non-aerated flow region. Overall, the study demonstrated the application of optical techniques to prototype spillway flows, provided that some careful validation was undertaken.