The Experts below are selected from a list of 120267 Experts worldwide ranked by ideXlab platform
Mats Leijon - One of the best experts on this subject based on the ideXlab platform.
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Power Coefficient measurement on a 12 kw straight bladed vertical axis wind turbine
Renewable Energy, 2011Co-Authors: Jon Kjellin, Mats Leijon, Fredrik Bulow, Sandra Eriksson, Paul Deglaire, Hans BernhoffAbstract:A 12 kW vertical axis H-rotor type wind turbine has been designed and constructed at Uppsala University. A measurement campaign has been performed to collect data to calculate the Power Coefficient using the method of bins. The measurement was performed at different constant rotational speeds on the turbine during varying wind speeds to observe the Power Coefficients dependence on tip speed ratio. The Power Coefficient peaked at 0.29 for a tip speed ratio equal to 3.3.
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a time dependent potential flow theory for the aerodynamics of vertical axis wind turbines
Journal of Applied Physics, 2005Co-Authors: Olov Agren, Marcus Berg, Mats LeijonAbstract:The Betz factor, i.e., the value 16∕27 for the Power Coefficient, is widely expected to give an upper limit for the performance of any wind turbine. In the present study, an analytical model of a vertical-axis wind turbine with straight vertical wings is developed. A goal of the work is to study if the one-dimensional Betz theory gives an upper limit of the performance of wind turbines when two-dimensional effects are included. The two-dimensional and time-dependent potential flow is solved by a conformal map of the wing sections to circles. The stagnation points are determined by the Kutta condition. The calculated Power Coefficient exceeds the Betz limit by a large factor. This is due to a completely different flow pattern compared to the one-dimensional Betz theory. In aerodynamic potential flow, the expanding flux tube of Betz is replaced by an asymptotic flow consisting of a superposition of homogeneous flow and a circulation around the wings. Moreover, the total torque on a turbine with three or mor...
M. Messina - One of the best experts on this subject based on the ideXlab platform.
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design of a vertical axis wind turbine how the aspect ratio affects the turbine s performance
international journal of energy and environmental engineering, 2014Co-Authors: S. Brusca, R. Lanzafame, M. MessinaAbstract:This work analyses the link between the aspect ratio of a vertical-axis straight-bladed (H-Rotor) wind turbine and its performance (Power Coefficient). The aspect ratio of this particular wind turbine is defined as the ratio between blade length and rotor radius. Since the aspect ratio variations of a vertical-axis wind turbine cause Reynolds number variations, any changes in the Power Coefficient can also be studied to derive how aspect ratio variations affect turbine performance. Using a calculation code based on the Multiple Stream Tube Model, symmetrical straight-bladed wind turbine performance was evaluated as aspect ratio varied. This numerical analysis highlighted how turbine performance is strongly influenced by the Reynolds number of the rotor blade. From a geometrical point of view, as aspect ratio falls, the Reynolds number rises which improves wind turbine performance.
John O Dabiri - One of the best experts on this subject based on the ideXlab platform.
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fish schooling as a basis for vertical axis wind turbine farm design
Bioinspiration & Biomimetics, 2010Co-Authors: Robert Whittlesey, Sebastian Liska, John O DabiriAbstract:Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high Power Coefficient (mechanical Power output divided by the Power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighboring turbines, HAWTs suffer from a reduced Power Coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's Power Coefficient when placed in close proximity to neighbors, thus yielding much higher Power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance Coefficient, which compares the expected average Power Coefficient of turbines in an array to a spatially isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance Coefficient based upon an array of 16 × 16 wind turbines. The results suggest increases in Power output of over one order of magnitude for a given area of land as compared to HAWTs.
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fish schooling as a basis for vertical axis wind turbine farm design
arXiv: Fluid Dynamics, 2010Co-Authors: Robert Whittlesey, Sebastian Liska, John O DabiriAbstract:Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high Power Coefficient (mechanical Power output divided by the Power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighbouring turbines, HAWTs suffer from a reduced Power Coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's Power Coefficient when placed in close proximity to neighbours, thus yielding much higher Power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance Coefficient, which compares the expected average Power Coefficient of turbines in an array to a spatially-isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance Coefficient based upon an array of 16x16 wind turbines. Results suggest increases in Power output of over one order of magnitude for a given area of land as compared to HAWTs.
Roger Lapuh - One of the best experts on this subject based on the ideXlab platform.
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low frequency ac dc voltage transfer standards with new high sensitivity and low Power Coefficient thin film multijunction thermal converters
IEEE Transactions on Instrumentation and Measurement, 2003Co-Authors: H Laiz, M Klonz, E Kessle, Maria Kampik, Roger LapuhAbstract:New planar multijunction thermal converters (PMJTCs) with low-Power Coefficient and high dynamic range using CuNi44/BiSbTe thermocouples have been manufactured. In series connection with carefully evaluated range resistors for voltages up to 1000 V they result in AC-DC voltage transfer standards with known AC-DC voltage transfer difference at low frequencies, for which the voltage step-up procedure is not necessary any more.
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low frequency ac dc voltage transfer standards with new high sensitivity and low Power Coefficient thin film multijunction thermal converters
Conference on Precision Electromagnetic Measurements, 2002Co-Authors: H Laiz, M Klonz, E Kessle, Maria Kampik, Roger LapuhAbstract:New Planar Multijunction Thermal Converters (PMJTC) with low Power Coefficient and high dynamic range using CuNi44/BiSbTe-thermocouples were developed. Together with carefully evaluated range resistors for voltages up to 1000 V they resulted in ac-dc transfer standards with negligible ac-dc voltage transfer difference at low frequencies. The measuring system was improved with a new highly stable low frequency voltage source.
R. Lanzafame - One of the best experts on this subject based on the ideXlab platform.
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design of a vertical axis wind turbine how the aspect ratio affects the turbine s performance
international journal of energy and environmental engineering, 2014Co-Authors: S. Brusca, R. Lanzafame, M. MessinaAbstract:This work analyses the link between the aspect ratio of a vertical-axis straight-bladed (H-Rotor) wind turbine and its performance (Power Coefficient). The aspect ratio of this particular wind turbine is defined as the ratio between blade length and rotor radius. Since the aspect ratio variations of a vertical-axis wind turbine cause Reynolds number variations, any changes in the Power Coefficient can also be studied to derive how aspect ratio variations affect turbine performance. Using a calculation code based on the Multiple Stream Tube Model, symmetrical straight-bladed wind turbine performance was evaluated as aspect ratio varied. This numerical analysis highlighted how turbine performance is strongly influenced by the Reynolds number of the rotor blade. From a geometrical point of view, as aspect ratio falls, the Reynolds number rises which improves wind turbine performance.
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horizontal axis wind turbine working at maximum Power Coefficient continuously
Renewable Energy, 2010Co-Authors: R. Lanzafame, Michele MessinaAbstract:Abstract The performance of a horizontal axis wind turbine continuously operating at its maximum Power Coefficient was evaluated by a calculation code based on Blade Element Momentum (BEM) theory. It was then evaluated for performance and Annual Energy Production (AEP) at a constant standard rotational velocity as well as at a variable velocity but at its maximum Power Coefficient. The mathematical code produced a Power coefficiency curve which showed that notwithstanding further increases in rotational velocity a constant maximum Power value was reached even as wind velocity increased. This means that as wind velocity varies there will always be a rotational velocity of the turbine which maximises its Coefficient. It would be sufficient therefore to formulate the law governing the variation in rotational velocity as it varied with wind velocity to arrive at a Power Coefficient that is always the same and its maximum. This work demonstrates the methodology for determining the law governing the rotational velocity of the rotor and it highlights the advantages of a wind turbine whose Power Coefficient is always at maximum rather than very variable in line with the variation of wind velocity.