Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A17: Energy Harvesting: General |
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Chair: Brian Polagye, University of Washington Room: 4c4 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A17.00001: Reliability Study of a Fully-Passive Oscillating-Foil Turbine Concept Waltfred Lee, Dylan Iverson, Guy Dumas, Peter Oshkai A self-sustained fully-passive flapping-foil hydrokinetic turbine prototype subjected to water flow at the Reynolds number of 21000 in a water channel. The prototype was exposed to three distinct types of flow disturbances: symmetric vortices shed from an oscillating foil placed upstream of the test foil, boundary layer tripping by distributed roughness on the surface of the foil, and freestream turbulence introduced via a fractal grid turbulence generator. The potential of power extraction of the foil undergoing elastically constrained oscillations in heave and pitch under these nonideal, unsteady flow conditions was quantified by implementing an eddy current brake. When placed in the wake of an upstream oscillating foil, the fully-passive turbine was sensitive to the frequency of the shed vortices in the incoming flow. Stable operation of the turbine could only be obtained under a limited range of kinematics of the upstream oscillating-foil. An overall increase in power extraction was observed when the turbine was subjected to the high freestream turbulence and when the surface roughness was applied. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A17.00002: Vortex Trajectory of High Pitch-High Heave Oscillating Hydrofoils Bernardo Luiz Rocha Ribeiro, Jennifer Franck Oscillating pitching and heaving foils have been shown to be an efficient mechanism for harvesting hydrokinetic energy. Due to the high pitch and heave amplitudes required for energy production, oscillating foils produce a wake of coherent vortices that interact with downstream foils in array configurations. In order to better predict the vortex-foil interactions, the formation and trajectory of the primary leading edge vortex (LEV) is explored computationally. The hydrofoil kinematics are varied with reduced frequencies of $fc/U_\infty = 0.1$ and $0.15$, with heave amplitudes of $0.5-2c$ and pitch amplitudes of $65^{\circ}-85^{\circ}$. The downstream position and timing of the LEV is relatively independent of Reynolds number, but it is strongly influenced by the kinematics. Differences in flapping frequency produce two different LEV trajectory patterns due to changes in the LEV structure during the heave stroke. At the higher frequency the LEV remains attached longer and thus has a lower convective speed in the wake. As the pitch amplitude is increased the LEV size and its trajectory's vertical distance increase linearly, however as the heave amplitude is increased the maximum vertical distance traveled by the LEV saturates non-linearly. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A17.00003: Experimental and Analytical Limitations of Blockage Corrections Hannah Ross, Brian Polagye Flow confinement can significantly impact the performance of wind and water turbines. These effects become appreciable if the blockage ratio, defined as the turbine's projected area divided by the cross-sectional area of the tunnel or channel, is larger than 5-10{\%}. Due to experimental and computational limitations, studies are often conducted at blockage ratios that exceed this threshold. To estimate performance in unconfined conditions, analytical corrections can be applied to data collected in confined flow. Multiple analytical corrections based on linear momentum theory have been proposed in the archival literature. A previous study by the authors explored the effectiveness of these corrections when applied to experimental data from an axial-flow turbine and a cross-flow turbine. We found that, overall, estimates for unconfined thrust coefficients were more accurate than estimates for unconfined power coefficients. Here, we explore possible causes for this discrepancy in performance. Specifically, we examine the influence that Reynolds dependence and the assumptions that underpin linear momentum theory have on the effectiveness of the power coefficient corrections. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A17.00004: Experimental evidence for coupled-mode flutter in a two-meter long parked wind turbine blade Pieter Boersma, Bridget Benner, Todd Currier, Yahya Modarres-Sadeghi We have conducted a series of experiments on a relatively large-scale wind turbine blade and observed coupled-mode flutter. Theoretical studies predict that the future wind turbine blades are susceptible to coupled-mode flutter. Experimental validation of this prediction is difficult, due to the inherent complications in conducting experimental work on structures that could become unstable due to flutter. We have built a relatively large (although small-scale compared to the 61-meter long full-scale blade) scale model of the NREL 5 MW blade from a flexible plastic. The blade was 2 meters long and was comprised of two 0.5 cm-thick shells bonded together such that the torsional natural frequency and the flapwise natural frequencies had a similar ratio to those in the full-scale. This was important, because the theoretical predictions suggest that the third flapwise and the first torsional natural frequencies coalesce into a coupled mode flutter mode. Our experimental results clearly show this coalescence and the resulting mode of oscillations in which a combined flapwise and torsional motion is observed. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A17.00005: Dynamics and coupling of inertial particles on the wake recovery and flow entrainment of a wind turbine Sarah Smith, Kristin Travis, Henda Djeridi, Martin Obligado, Raúl Bayoán Cal Impacting particles such as rain, dust, and other debris can have devastating structural effects on wind turbines, but little is known about the interaction of such debris within turbine wakes. This study aims to characterize behavior of inertial particles within the axisymmetric turbulent wake of a wind turbine and the resulting effects on wake recovery. Here a model wind turbine is subjected to varied two-phase inflow conditions with wind as the carrier fluid ($Re_D = 17.7*10^3 - 39.3*10^3$) and polydisperse water droplets (averaging 60 micrometers in diameter) at varied concentrations ( $\phi_v = 9.7*10^{-6} - 2.6*10^{-5}$). Phase doppler interferometry (PDI) and particle image velocimetry (PIV) were employed at multiple downstream locations, centered with respect to turbine hub height. Analysis considers energy and particle size distribution within the wake focusing on particle entrainment, settling velocity, and preferential concentration. Near wake statistics show similarities to those of turbines in single-phase flows, and show persisting velocity deficits at least as far as 9.5 rotor diameters downstream. Complex particle behavior is evident in the near wake region where small particles are captured within tip vortices and central wake regions. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A17.00006: Wind Turbine Icing Physics and A Novel Strategy for Wind Turbine Icing Mitigation Linyue Gao, Hui Hu Wind turbine icing represents the most significant threat to the integrity of wind turbines in cold weather. By leveraging the Icing Research Tunnel available at Iowa State University (ISU-IRT), an experimental study was conducted to elucidate the underlying physics of the important micro-physical processes pertinent to wind turbine phenomena and explore novel anti-/de-icing strategies for wind turbine icing mitigation. A suite of advanced flow diagnostic techniques, which include molecular tagging velocimetry and thermometry (MTV{\&}T), digital image projection (DIP), and infrared (IR) imaging thermometry, were developed and applied to quantify the transient behavior of wind-driven surface water film/rivulet flows, unsteady heat transfer and dynamic ice accreting process over the surfaces of wind turbine blade models. A novel, hybrid anti-/de-icing strategy that combines minimized electro-heating at the blade leading edge and an ice-phobic coating to cover the blade surface was developed for wind turbine icing mitigation. In comparison to the conventional strategy to brutally heating the mass blade surface to keep the blade ice free, the hybrid strategy was demonstrated to be able to achieve the same anti-/de-icing performance with substantially less power consumption (i.e., up to \textasciitilde 90{\%} power saving). [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A17.00007: Reduced-order transport models for energy and the environment Zhong Zheng We present recent developments on reduced-order modelling and its applications to energy and environmental processes, such as geological CO$_2$ sequestration and hydraulic fracturing, which is related to the application of energy resource recovery, such as shale gas recovery. In particular, we introduce a series of gravity current models, which describe the spreading and draining dynamics of supercritical CO$_2$ that is injected into a saline aquifer, for example. In many situations we consider here, self-similar solutions are available to describe some of the interesting dynamics, considering the effects of buoyancy, surface tension, and heterogeneity, for example. We next introduce a series of experimental work that is related to the dynamics of hydraulic fracturing. Model viscous fluids and elastic solids have been employed for the laboratory-scale experiments, and scaling argument has been performed to describe the spatial and temporal evolution of the hydraulic fractures and some of the parametric dependence. We also point out several future research directions and hopefully bring in more interests on this topic. [Preview Abstract] |
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