The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Hans Berhnoff - One of the best experts on this subject based on the ideXlab platform.
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simulating pitching blade with free Vortex Model coupled with dynamic stall Model for conditions of straight bladed vertical axis turbines
Journal of Solar Energy Engineering-transactions of The Asme, 2015Co-Authors: Eduard Dyachuk, Anders Goude, Hans BerhnoffAbstract:This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical Models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the Modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies. An existing dynamic stall Model was investigated and further modified for the conditions of the VAWT operation. This Model was coupled with a streamtube Model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube Model has been improved compared to its previous versions. The dynamic stall Model was further modified by coupling it with a free Vortex Model. The new Model has become less dependent on empirical constants and has shown an improved accuracy. Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified.The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved Vortex Model has been validated against the data from the new measurements. The Model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented Vortex Model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.
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simulating pitching blade with free Vortex Model coupled with dynamic stall Model for conditions of straight bladed vertical axis turbines
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Eduard Dyachuk, Anders Goude, Hans BerhnoffAbstract:This study is on the straight bladed vertical axis turbines, which can be utilized for both wind and marine current energy. Vertical axis turbines have the potential of lower installation and maintenance cost. However, complex unsteady fluid mechanics of these turbines imposes significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions, and it is in the focus of the study. The dynamic stall effects are very important for vertical axis turbines, since they are usually passively controlled through the dynamic stall. A free Vortex Model is used to calculated unsteady attached flow, while the separated flow is handled by the dynamic stall Model. This is compared to the Model based solely on the Leishman-Beddoes algorithm. The results are assessed against the measured data on pitching airfoils. A comparison of force coefficients between the simulations and experiments is done at the conditions similar to the conditions of H-rotor type vertical axis turbines.Copyright © 2014 by ASME
P. Henrik Alfredsson - One of the best experts on this subject based on the ideXlab platform.
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A simplified Vortex Model of propeller and wind-turbine wakes
Journal of Fluid Mechanics, 2013Co-Authors: Antonio Segalini, P. Henrik AlfredssonAbstract:A new Vortex Model of inviscid propeller and wind-turbine wakes is proposed based on an asymptotic expansion of the Biot-Savart induction law to account for the finite Vortex core size. The circulation along the blade is assumed to be constant from the blade root to the tip approximating a turbine with maximum power production for given operating conditions. The Model iteratively calculates the tip-Vortex path, allowing the wake to expand/contract freely, and is afterward able to evaluate the velocity field in the whole domain. The 'roller-bearing analogy', proposed by Okulov and Sorensen (J. Fluid Mech., vol. 649, 2010, pp. 497-508), is used to determine the Vortex core size. A comparison of the main outcomes of the present Model with the general momentum theory is performed in terms of the operating parameters (namely the number of blades, the tip-speed ratio, the blade circulation and the Vortex core size), demonstrating good agreement between the two. Furthermore, experimental data have been compared with the Model outputs to validate the Model under real operating conditions.
Rudolf Friedrich - One of the best experts on this subject based on the ideXlab platform.
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Generalized Vortex Model for the inverse cascade of two-dimensional turbulence.
Physical review. E Statistical nonlinear and soft matter physics, 2013Co-Authors: Jan Friedrich, Rudolf FriedrichAbstract:We generalize Kirchhoff's point Vortex Model of two-dimensional fluid motion to a rotor Model which exhibits an inverse cascade by the formation of rotor clusters. A rotor is composed of two vortices with like-signed circulations glued together by an overdamped spring. The Model is motivated by a treatment of the vorticity equation representing the vorticity field as a superposition of vortices with elliptic Gaussian shapes of variable widths, augmented by a suitable forcing mechanism. The rotor Model opens up the way to discuss the energy transport in the inverse cascade on the basis of dynamical systems theory.
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Lagrangian particle statistics in turbulent flows from a simple Vortex Model.
Physical Review E, 2008Co-Authors: Michael Wilczek, Frank Jenko, Rudolf FriedrichAbstract:The statistics of Lagrangian particles in turbulent flows is considered in the framework of a simple Vortex Model. Here, the turbulent velocity field is represented by a temporal sequence of Burgers vortices of different circulation, strain, and orientation. Based on suitable assumptions about the vortices' statistical properties, the statistics of the velocity increments is derived. In particular, the origin and nature of small-scale intermittency in this Model is investigated both numerically and analytically. We critically compare our results to experimental studies.
Eduard Dyachuk - One of the best experts on this subject based on the ideXlab platform.
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simulating pitching blade with free Vortex Model coupled with dynamic stall Model for conditions of straight bladed vertical axis turbines
Journal of Solar Energy Engineering-transactions of The Asme, 2015Co-Authors: Eduard Dyachuk, Anders Goude, Hans BerhnoffAbstract:This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical Models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the Modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies. An existing dynamic stall Model was investigated and further modified for the conditions of the VAWT operation. This Model was coupled with a streamtube Model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube Model has been improved compared to its previous versions. The dynamic stall Model was further modified by coupling it with a free Vortex Model. The new Model has become less dependent on empirical constants and has shown an improved accuracy. Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified.The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved Vortex Model has been validated against the data from the new measurements. The Model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented Vortex Model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.
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simulating pitching blade with free Vortex Model coupled with dynamic stall Model for conditions of straight bladed vertical axis turbines
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Eduard Dyachuk, Anders Goude, Hans BerhnoffAbstract:This study is on the straight bladed vertical axis turbines, which can be utilized for both wind and marine current energy. Vertical axis turbines have the potential of lower installation and maintenance cost. However, complex unsteady fluid mechanics of these turbines imposes significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions, and it is in the focus of the study. The dynamic stall effects are very important for vertical axis turbines, since they are usually passively controlled through the dynamic stall. A free Vortex Model is used to calculated unsteady attached flow, while the separated flow is handled by the dynamic stall Model. This is compared to the Model based solely on the Leishman-Beddoes algorithm. The results are assessed against the measured data on pitching airfoils. A comparison of force coefficients between the simulations and experiments is done at the conditions similar to the conditions of H-rotor type vertical axis turbines.Copyright © 2014 by ASME
Johan Meyers - One of the best experts on this subject based on the ideXlab platform.
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Validation of four LES and a Vortex Model against stereo-PIV measurements in the near wake of an actuator disc and a wind turbine
Renewable Energy, 2016Co-Authors: L. E. M. Lignarolo, Daniele Ragni, Gijs Van Kuik, Søren Juhl Andersen, Dhruv Mehta, Richard J. A. M. Stevens, Ali Emre Yilmaz, Charles Meneveau, Carlos J. Ferreira, Johan MeyersAbstract:In this paper we report the results of a workshop organised by the Delft University of Technology in 2014, aiming at the comparison between different state-of-the-art numerical Models for the simulation of wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereoscopic Particle Image Velocimetry was employed to obtain the velocity field and turbulence statistics in the near wake of a two-bladed wind turbine Model and of a porous disc, which mimics the numerical actuator used in the simulations. Researchers have been invited to simulate the experimental case based on the disc drag coefficient and the inflow characteristics. Four large eddy simulation (LES) codes from different institutions and a Vortex Model are part of the comparison. The purpose of this benchmark is to validate the numerical predictions of the flow field statistics in the near wake of an actuator disc, a case that is highly relevant for full wind farm applications. The comparison has shown that, despite its extreme simplicity, the Vortex Model is capable of reproducing the wake expansion and the centreline velocity with very high accuracy. Also all tested LES Models are able to predict the velocity deficit in the very near wake well, contrary to what was expected from previous literature. However, the resolved velocity fluctuations in the LES are below the experimentally measured values.
