Control experiments with a semi-axisymmetric supercavity and a supercavity-piercing fin

Supercavitation can significantly reduce skin-friction drag on an underwater body, thus enabling a dramatic increase in attainable velocity. The control of a High-Speed Supercavitating Vehicle (HSSV) poses unique challenges, since only small regions at the nose (cavitator) and on the afterbody (fins) are in contact with water and can be used as control surfaces. The interaction between supercavity dynamics and control surface actuation is complex and nonlinear. Experiments were conducted with a semi-axisymmetric, ventilated supercavity and a single wedge-shaped, 45 degree swept, cavitypiercing fin in the high-speed water tunnel at St. Anthony Falls Laboratory. Motion control was combined with water tunnel testing to create a hardware-in-the-loop system that can (a) provide critical hydrodynamic parameters for control models and (b) serve as a test bed for fin control strategies. Through a series of experiments, control surfacecavity interaction, cavity stability and hysteresis effects were studied. Fin torque (lift) was measured for different angles of attack with varying cavitation numbers. Closed-loop fin control experiments simulating simple maneuvers were carried out.http://deepblue.lib.umich.edu/bitstream/2027.42/84319/1/CAV2009-final146.pd

A parametric evaluation of the interplay between geometry and scale on cross-flow turbine performance

Cross-flow turbines harness kinetic energy in wind or moving water. Due to their unsteady fluid dynamics, it can be difficult to predict the interplay between aspects of rotor geometry and turbine performance. This study considers the effects of three geometric parameters: the number of blades, the preset pitch angle, and the chord-to-radius ratio. The relevant fluid dynamics of cross-flow turbines are reviewed, as are prior experimental studies that have investigated these parameters in a more limited manner. Here, 223 unique experiments are conducted across an order of magnitude of diameter-based Reynolds numbers ($\approx 8\!\times\!10^4 - 8\!\times\!10^5$) in which the performance implications of these three geometric parameters are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space identifies new parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. Because these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. Results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models.Comment: SUBMITTED to Renewable and Sustainable Energy Review

Entropy Analysis in Pipe Flow Subjected to External Heating

Abstract: In the present study, heat transfer and entropy analysis for flow through a pipe system is considered. The Reynolds number and the pipe wall temperature effects on entropy distribution and total entropy generation in the pipe are investigated. Numerical scheme employing a control volume approach is introduced when solving the governing equations. Steel is selected as pipe material, while water is used as fluid. It is found that increasing pipe wall temperature and Reynolds number increases the entropy production rate, in which case, entropy generation due to heat transfer dominates over that corresponding to fluid friction

DNS study of a pipe flow following a step increase in flow rate

Direct numerical simulation (DNS) is conducted to study the transient flow in a pipe following a near-step increase of flow rate from an initial turbulent flow. The results are compared with those of the transient flow in a channel reported in He and Seddighi (2013). It is shown that the flow again exhibits a laminar–turbulent transition, similar to that in a channel. The behaviours of the flow in a pipe and a channel are the same in the near-wall region, but there are significant differences in the centre of the flow. The correlation between the critical Reynolds number and free stream turbulence previously established for a channel flow has been shown to be applicable to the pipe flow. The responses of turbulent viscosity, vorticity Reynolds number, and budget terms are analysed. Some significant differences have been found to exist between the developments of the vorticity Reynolds number in the pipe and channel flows

An Energy-Water Corridor Along the US/Mexico Border: Changing the \u27Conversation\u27

Over the last decade, migration has become a divisive issue around the world. A large number of countries have erected barriers along their borders to prevent migration, leading to geopolitical tension. Climate change effects will likely exacerbate migration tensions, which will require bold and creative solutions to this difficult social predicament. Here we detail a plan to construct an energy-water corridor along a border that has been the focus of much attention recently: The U.S.-Mexico border. Our proposed solution helps to alleviate some of the negative effects of climate change, while providing energy and economic stimulus to an area that begs for sustainable development. The energy-water corridor will take advantage of the unique renewable energy resources along the border states and will use state-of-the-art water desalination and treatment systems to provide the resources for economic development in the region

Vater an seinem Lebensabend

Aus dem Japanischen von Kathrin Wosnik. Vorlage der Übersetzung: Kobori Annu: Bannen no Chich