Detailed instantaneous velocity fields of a jet in crossflow have been measured with stereoscopic particle image velocimetry (PIV). The jet originated from a fully developed turbulent pipe flow and entered a crossflow with a turbulent boundary layer. The Reynolds number based on crossflow velocity and pipe diameter was 2400 and the jet to crossflow velocity ratios wereR=3.3 andR=1.3. The experimental data have been analysed by proper orthogonal decomposition (POD). ForR=3.3, the results in several different planes indicate that the wake vortices are the dominant dynamic flow structures and that they interact strongly with the jet core. The analysis identifies jet shear-layer vortices and finds that these vortical structures are more local and thus less dominant. ForR=1.3, on the other hand, jet shear-layer vortices are the most dominant, while the wake vortices are much less important. For both cases, the analysis finds that the shear-layer vortices are not coupled to the dynamics of the wake vortices. Finally, the hanging vortices are identified and their contribution to the counter-rotating vortex pair (CVP) and interaction with the newly created wake vortices are described.
Topology optimised designs for passive cooling of light-emitting diode (LED) lamps are investigated through extensive numerical parameter studies. The designs are optimised for either horizontal or vertical orientations and are compared to a lattice-fin design. The different orientations result in significant differences in topologies. The optimisation favors placing material at outer boundaries of the design domain, leaving a hollow core that allows the buoyancy forces to accelerate the air to higher speeds. Investigations show that increasing design symmetry yields performance with less sensitivity to orientation with a minor loss in mean performance. The topology-optimised designs of heat sinks for natural convection yield a 26% lower package temperature using around 12% less material compared to the lattice-fin design, while maintaining low sensitivity to orientation. Furthermore, they exhibit several defining features and provide insight and general guidelines for the design of passive coolers for LED lamps.
The exhalant jet flow of mussels in conjunction with currents and/or other mussels may strongly influence the mussels' grazing impact. Literature values of mussel exhalant jet velocity vary considerably and the detailed fluid mechanics of the near-mussel flow generated by the exhalant jet has hitherto been uncertain. Computational modelling of this phenomenon depends on knowledge of the velocity distribution near the exhalant siphon aperture of mussels to provide appropriate boundary conditions for numerical flow models. To be useful such information should be available for a range of mussel shell lengths. Here, we present results of a detailed study of fully open mussels Mytilus edulis in terms of filtration rate, exhalant siphon aperture area, jet velocity, gill area and body dry weight, all as a function of shell length (mean ± SD) over the range 16.0 ± 0.4 to 82.6 ± 2.9 mm, with the corresponding scaling laws also presented. The exhalant jet velocity was determined by 3 methods: (1) measured clearance rate divided by exhalant aperture area, (2) manual particle tracking velocimetry (PTV) using video-microscope recordings, and (3) particle image velocimetry (PIV). The latter provides detailed 2-component velocity distributions near the exhalant siphon in 5 planes parallel to the axis of the jet and the major axis of the oval aperture, and hence estimates of momentum and kinetic energy flows in addition to mean velocity. Data obtained on particles inside the exhalant jet of filtered water was verified by the use of titanium dioxide seeding particles which were de-agglomerated by ultrasound to a size range of 0.7 to 2 µm prior to addition, to avoid retention by the gill filter of the mussels. We found that exhalant jet velocity was essentially constant at ~8 cm s −1 , and independent of shell length. Based on geometric similarity and scaling of mussel pump-system characteristics we found that these characteristics coincide approximately for all sizes when expressed as pressure head versus volume flow divided by shell length squared. KEY WORDS: Filtration rate · Exhalant siphon area · Particle image velocimetry · Particle tracking velocimetry · Exhalant jet velocity · Velocity field · Allometric equation · Scaling law Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 437: [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163][164] 2011 will influence the grazing impact and thus the concentration distribution of food particles reaching the inhalant aperture; hence affecting the feeding conditions of the mussel. Of particular interest is the undesirable phenomenon of re-filtration where part of the once filtered and exhaled water reaches the inhalant aperture of either the same or other mussels. This has been studied to some extent for mussel beds where a number of attempts have been made to model phytoplankton concentration gradients caused by dense beds of filter-feeding bivalves in relatively strong currents with a high ...
The turbulent and swirling flow of a uniflowscavenged two-stroke engine cylinder is investigated using a scale model with a static geometry and a transparent cylinder. The swirl is generated by 30 equally spaced ports with angles of 0°, 10°, 20°, and 30°. A detailed characterization of the flow field is performed using stereoscopic particle image velocimetry. Mean fields are calculated using both a fixed coordinate system and a coordinate system based on the instantaneous flow topology. Timeresolved measurements of axial velocity are performed with laser Doppler anemometry, and power spectra are calculated in order to determine vortex core precession frequencies. The results show a very different flow dynamics for cases with weak and strong swirl. In the strongly swirling cases, a vortex breakdown is observed. Downstream of the breakdown, the vortex becomes highly concentrated and the vortex core precesses around the exhaust valve, resulting in an axial suction effect at the vortex center. Mean fields based on the instantaneous flow topology are shown to be more representative than mean fields based on a fixed coordinate system in cases with significant variations in the swirl center location.
Lighting is an essential requisite for the industrial world but consumes vast amounts of energy. Hence, even minimal savings in energy consumption of lighting devices may have a significant effect on cost and environmental impact. Here we demonstrate a computer-aided approach for optimizing passive heat sinks for light-emitting diode (LED) lamps. Efficient passive cooling ensures lower energy consumption, increased lifetime and reduced maintenance costs of this rapidly growing, expectedly soon to be governing, lighting technology. Highly efficient cooling structures are generated by topology optimization, a computational morphogenesis approach with ultimate design freedom, relying on high-performance computing and simulation. The optimized devices, exhibiting complex and organiclooking topologies not unlike corals, are manufactured by additive manufacturing technology. Numerical simulations confirmed by experiments indicate that topology-optimized designs may outperform traditional pin-like geometries by more than 21%, resulting in a doubling of life expectancy and 50% decrease in operational cost.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.