Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E28: Wind Turbines: Actuator Lines/Discs |
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Chair: Ralf Deiterding, University of Southampton Room: 309 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E28.00001: Predictive simulation of wind turbine wake interaction with an adaptive lattice Boltzmann method for moving boundaries Ralf Deiterding, Stephen L. Wood Operating horizontal axis wind turbines create large-scale turbulent wake structures that affect the power output of downwind turbines considerably. The computational prediction of this phenomenon is challenging as efficient low dissipation schemes are necessary that represent the vorticity production by the moving structures accurately and are able to transport wakes without significant artificial decay over distances of several rotor diameters. We have developed the first version of a parallel adaptive lattice Boltzmann method for large eddy simulation of turbulent weakly compressible flows with embedded moving structures that considers these requirements rather naturally and enables first principle simulations of wake-turbine interaction phenomena at reasonable computational costs. The presentation will describe the employed algorithms and present relevant verification and validation computations. For instance, power and thrust coefficients of a Vestas V27 turbine are predicted within 5\% of the manufacturer’s specifications. Simulations of three Vestas V27-225kW turbines in triangular arrangement analyze the reduction in power production due to upstream wake generation for different inflow conditions. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E28.00002: A new class of actuator surface models incorporating wind turbine blade and nacelle geometry effects Xiaolei Yang, Fotis Sotiropoulos It was shown by Kang, Yang and Sotiropoulos (Journal of Fluid Mechanics 744 (2014): 376-403.) that the nacelle has significant effects on the turbine wake even in the far wake region, which the standard actuator line model is not able to predict. We develop a new class of actuator surface models for the blades and nacelle, which is able to resolve the effects of both tip vortices and nacelle vortex. The new nacelle model, which is based on distributing forces from the actual nacelle geometry as in the diffused interface immersed boundary methods, is first tested by carrying out LES of the flow past a sphere and demonstrating good agreement with available in the literature DNS results. The proposed model is subsequently validated by simulating the flow past the hydrokinetic turbine used in the simulations of Kang et al. and good agreement with the measurements is demonstrated. Finally, the proposed model is applied to utility scale wind turbines to elucidate the role of nacelle vortex dynamics on turbine wake meandering. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E28.00003: Simulating wind and marine hydrokinetic turbines with actuator lines in RANS and LES Peter Bachant, Martin Wosnik As wind and marine hydrokinetic (MHK) turbine designs mature, focus is shifting towards improving turbine array layouts for maximizing overall power output, i.e., minimizing wake interference for axial-flow or horizontal-axis turbines, or taking advantage of constructive wake interaction for cross-flow or vertical-axis turbines. Towards this goal, an actuator line model (ALM) was developed to provide a computationally feasible method for simulating full turbine arrays inside Navier--Stokes models. The ALM predicts turbine loading with the blade element method combined with sub-models for dynamic stall and flow curvature. The open-source software is written as an extension library for the OpenFOAM CFD package, which allows the ALM body force to be applied to their standard RANS and LES solvers. Turbine forcing is also applied to volume of fluid (VOF) models, e.g., for predicting free surface effects on submerged MHK devices. An additional sub-model is considered for injecting turbulence model scalar quantities based on actuator line element loading. Results are presented for the simulation of performance and wake dynamics of axial- and cross-flow turbines and compared with moderate Reynolds number experiments and body-fitted mesh, blade-resolving CFD. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E28.00004: Determining the optimal smoothing length scale for actuator line models of wind turbine blades Luis Martinez, Charles Meneveau The actuator line model (ALM) is a widely used tool for simulating wind turbines when performing Large-Eddy Simulations. The ALM uses a smearing kernel $\eta_\epsilon = {1}/{\epsilon^3 \pi^{3/2}}\exp{\left(-r^2/\epsilon^2\right)}$, where $r$ is the distance to an actuator point, and $\epsilon$ is the smoothing length scale which establishes the kernel width, to project the lift and drag forces onto the grid. In this work, we develop formulations to establish the optimum value of the smoothing length scale $\epsilon$, based on physical arguments, instead of purely numerical constraints. This parameter has a very important role in the ALM, to provide a length scale, which may, for example, be related to the chord of the airfoil being studied. In the proposed approach, we compare features (such as vertical pressure gradient) of a potential flow solution for flow over a lifting surface with features of the solution of the Euler equations with a body force term. The potential flow solution over a lifting surface is used as a general representation of an airfoil. The method presented aims to minimize the difference between these features of the flow fields as a function of the smearing length scale ($\epsilon$), in order to obtain the optimum value. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E28.00005: Enhanced Actuator Line Simulation of a Wind Turbine by including the Conservative Load at the Blade Tip Ivan Herraez, Daniel Micallef, Gijs A. M. van Kuik, Joachim Peinke At the tip of wind turbine blades, the radial bound circulation is transformed into chordwise circulation just before being released as trailing vorticity, giving rise to the tip vortex. The force acting on the chordwise circulation contains a radial and a normal component with respect to the blade axis. This load does not contribute to the torque, so it is a conservative load. Due to this, it is disregarded in the engineering tools used for the design of wind turbines. However, as we demonstrated in a previous work, the conservative load might influence the trajectory of the tip vortex. In order to see how this affects the blade loads, in this research we perform large eddy simulations with an actuator line model where the conservative load has been included. The conservative load reduces the angle of attack in the tip region as a consequence of the modified tip vortex trajectory. This has a negative influence on the lift and the power output. We conclude that the accuracy of engineering design tools of wind turbines can be improved if the conservative load acting at the tip is considered. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E28.00006: Development of an advanced actuator disk model for Large-Eddy Simulation of wind farms Maud Moens, Matthieu Duponcheel, Gregoire Winckelmans, Philippe Chatelain This work aims at improving the fidelity of the wind turbine modelling for Large-Eddy Simulation (LES) of wind farms, in order to accurately predict the loads, the production, and the wake dynamics. In those simulations, the wind turbines are accounted for through actuator disks. i.e. a body-force term acting over the regularised disk swept by the rotor. These forces are computed using the Blade Element theory to estimate the normal and tangential components (based on the local simulated flow and the blade characteristics). The local velocities are modified using the Glauert tip-loss factor in order to account for the finite number of blades; the computation of this correction is here improved thanks to a local estimation of the effective upstream velocity at every point of the disk. These advanced actuator disks are implemented in a 4th order finite difference LES solver and are compared to a classical Blade Element Momentum method and to high fidelity wake simulations performed using a Vortex Particle-Mesh method in uniform and turbulent flows. [Preview Abstract] |
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