Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E24: Wind Turbines: Wind Farms |
Hide Abstracts |
Chair: Johan Meyers, Katholieke University, Leuven Room: 2003 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E24.00001: Coupled wake boundary layer model of windfarms Richard Stevens, Dennice Gayme, Charles Meneveau We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. [Preview Abstract] |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E24.00002: Temporal characteristics of POD modes from wind farm LES Claire VerHulst, Charles Meneveau Large eddy simulations of a fully developed wind farm in the turbulent atmospheric boundary layer have been analyzed using 3D Proper Orthogonal Decomposition (POD). In this study we consider the temporal variations of the POD modes and their relationship to unsteadiness in the wind turbine power production. We find that the streamwise-constant counter-rotating roller modes vary on time-scales much longer that the mean advection time from turbine to turbine. The structure of these roller modes and their long-time variations are consistent with meandering of high- and low-speed streaks in the turbulent flow within the wind farm. Another class of POD modes---one with significant streamwise-variation---is found to correspond to advection of velocity perturbations in the streamwise direction. Temporal variations of the shear-type modes are found to strongly correlate with power production of the wind farm as a whole. Overall, the long-time power production is well captured by reconstructions using fewer than 50 POD modes ($< 1$\% of the total), but variations faster than the inter-turbine advection time are only captured by higher-order, less energetic modes. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E24.00003: A geometry-based approach for optimizing wind turbine layout Niranjan Ghaisas, Cristina Archer Layout studies are critical in designing large wind farms, since wake effects can lead to significant reductions in wind power generation. Optimizing wind farm layout using computational fluid dynamics is practically unfeasible today because of the high computational requirements of the numerical simulations. Simple statistical models, based on geometric quantities associated with the wind farm layout, are therefore attractive because they are less demanding computationally. Results of large-eddy simulations of the Lillgrund wind farm are used here to develop such geometry-based models. Several geometric quantities (e.g., blockage ratio, or the fraction of the swept-area of a wind turbine which is blocked by upstream turbines) are found to correlate very well ($>$ 0.95) with the power generated by the turbines. These models are particularly accurate at predicting the farm-averaged power and are therefore used here to study layout effects in large wind farms. Several layout parameters are considered, such as angle between rows and columns, turbine spacing, staggering of alternate rows, and wind direction. This study demonstrates the utility of simple, inexpensive, and reasonably accurate geometric models to identify general principles governing optimal wind farm layout. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E24.00004: Optimal control of energy extraction in LES of large wind farms Johan Meyers, Jay Goit, Wim Munters We investigate the use of optimal control combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large ``infinite'' wind farms and in finite farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with an actuator-disk representation of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in the actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. In a first infinite wind-farm case, we find that farm power is increases by approximately 16\% over one hour of operation. This comes at the cost of a deceleration of the outer layer of the boundary layer. A detailed analysis of energy balances is presented, and a comparison is made between infinite and finite farm cases, for which boundary layer entrainment plays an import role. [Preview Abstract] |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E24.00005: An ideal limit for the performance of a large, fully-developed wind farm P. Luzzatto-Fegiz, C.P. Caulfield Wind turbines are often deployed in arrays of hundreds of units, where interactions lead to drastic losses in power output. Remarkably, while the theoretical ``Betz'' maximum has long been established for the output of a single turbine, no corresponding theory appears to exist for a generic, large-scale energy extraction system, although models exist for specific turbine designs and layouts. Recent work with vertical-axis turbines indicates that large performance gains may be achievable (Dabiri 2011), making the search for a theoretical upper bound even more compelling. We develop a model for an array of energy-extraction devices of arbitrary design and layout, first focusing on the fully-developed regime. When tailoring the model to reflect current designs, the predicted power output is in good agreement with field measurements. Furthermore, by considering a suitable ideal limit, we establish an upper bound on the performance of a large wind farm. This is found to be several times larger than the output of existing arrays, thus supporting the notion that performance improvements may be possible. Finally, we extend our model to include spatially developing flows, as well as to account for the effect of atmospheric stability, finding good agreement with laboratory and field data. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E24.00006: Effect of the tip speed ratio in the power production of aligned wind turbines Kenneth Carrasquillo, Christian Santoni, Mario Rotea, Yaoyu Li, Stefano Leonardi The increased demand for wind energy had led to a constant increase in the size of wind turbines and subsequently of the wind farms. A drawback of using large arrays of wind turbines is the decrease in efficiency due to the wake interference. For example, the second row of turbines extracts about 15{\%} less power than the first row. Previous studies indicated that the power production of the entire wind farm is not maximized if the turbines work at their optimum tip speed ratio (TSR). In fact, reducing the TSR on the upwind turbines with respect to an optimum value, the momentum deficit decreases and the downwind turbines power production increases. Although the power production on the upwind turbines decreases, the power production of the entire wind plant may increase. Large Eddy Simulations of the turbulent flow over three NREL5MW aligned turbines have been performed. The most downwind turbine is kept at maximum power production with TSR$=$7.5, while the TSR of the other two turbines is varied. The effect of the TSR on power production and its fluctuations will be discussed. The UTDWF code is used to perform the simulations, which is based on a finite difference scheme with the Line Actuator to model the turbine blades and the Immersed Boundary Method for the tower and nacelle. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700