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Near-wake dynamics of a vertical-axis turbine
- Benjamin Strom, Brian Polagye, Steven L. Brunton
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- Journal:
- Journal of Fluid Mechanics / Volume 935 / 25 March 2022
- Published online by Cambridge University Press:
- 25 January 2022, A6
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- Article
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Cross-flow, or vertical-axis, turbines are a promising technology for capturing kinetic energy in wind or flowing water and their inherently unsteady fluid mechanics present unique opportunities for control optimization of individual rotors or arrays. To explore the potential for beneficial interactions between turbines in an array, as well as to characterize important cycle-to-cycle variations, coherent structures in the wake of a single two-bladed cross-flow turbine are examined using planar stereo particle image velocimetry in a water channel experiment. There are three main objectives in the present work. First, the mean wake structure of this high chord-to-radius ratio rotor is described, compared with previous studies, and a simple explanation for observed wake deflection is presented. Second, the unsteady flow is then analysed via the triple decomposition, with the periodic component extracted using a combination of traditional techniques and a novel implementation of the optimized dynamic mode decomposition. The latter method is shown to outperform conditional averaging and Fourier methods, as well as uncover frequencies suggesting a transition to bluff-body shedding in the far wake. Third, vorticity and finite-time Lyapunov exponents are then employed to further analyse the oscillatory wake component. Vortex streets on both sides of the wake are identified, and their formation mechanisms and effects on the mean flow are discussed. Strong axial (vertical) flow is observed in vortical structures shed on the retreating side of the rotor where the blades travel downstream. Time-resolved tracking of these vortices is performed, which demonstrates that vortex trajectories have significant rotation-to-rotation variation within one diameter downstream. This variability suggests it would be challenging to harness or avoid such structures at greater downstream distances.
The Appropriate Role of Computerized Postmarketing Surveillance
- Brian L. Strom
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- Journal:
- CNS Spectrums / Volume 12 / Issue S16 / 2007
- Published online by Cambridge University Press:
- 07 November 2014, pp. 3-7
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Pharmacoepidemiology, the study of the effects of drugs in large numbers of people, is a relatively new discipline that applies the methods of epidemiology to clinical pharmacology. Premarketing clinical trials remain the only way to scientifically determine whether a drug is causally effective, yet these trials do not provide information that allows for estimates about rare, late, or off-label toxicities associated with the drug in question. Increasing concern about common and debilitating adverse effects of medications has highlighted the need for enhanced postmarketing surveillance to follow up on clinical trials. There is a further concern regarding the broader issue of the risk-benefit ratio of certain medications. Computerized databases are a good source of information on which to lay the foundations of postmarketing research. A system of cross-linked computerized medical records may better enable researchers and physicians to realistically monitor postmarketing safety and incorporate monitoring benefits. The same research could also elucidate the net public health effect of regulatory decisions. The Veterans Affairs database in the United States and PHARMO in the Netherlands may represent good models on which to base future postmarketing surveillance studies.
In this expert roundtable supplement, Brian L. Strom, MD, provides an overview of the appropriate use of large computer databases in pharmacoepidemiology studies. Philip Wang, MD, DrPH, discusses the advantages of pharmacoepidemiologic studies over clinical trials in correctly detecting drug safety issues. Francesca Cunningham, PharmD, reviews a large computer database that is currently in use within the VA healthcare system, and Ron M.C. Herings, PharmD, PhD, discusses the development of the PHARMO system in the Netherlands.
This summary is based heavily on the concepts presented in: Strom BL. What is pharmacoepidemiology. In: Strom BL, ed. Pharmacoepidemiology. 4th ed. Sussex: John Wiley; 2005:3–15; and Strom BL. Overview of study designs available for pharmacoepidemiology studies. In: Strom BL, ed. Pharmacoepidemiology. 4th ed. Sussex: John Wiley, 2005:17–28.