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 L42: Boundary Layers: Wind Turbine Interactions II |
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Chair: Luciano Castillo, Purdue University Room: 6e |
Monday, November 25, 2019 1:45PM - 1:58PM |
L42.00001: Effect of complex terrain on the performance of wind farms Richard Stevens, Luoqin Liu We use a newly developed wall modeled immersed boundary method for large-eddy simulations to study the performance of wind farms in complex terrain. The method is validated against wind tunnel measurements for flow over a 2D ridge and a 3D hill. First, we analyze the performance of a single wind turbine in the vicinity of a ridge. For turbines that are significantly taller than the ridge, the performance improves as the flow speeds-up over the ridge. The impact of the hill on the performance of short turbines depends on the turbine location. The turbine performance is better at the hilltop. However, the performance of turbines located in front of the ridge is impacted due to blockage effects. Secondly, we consider a wind farm with a ridge in the middle. The ridge wake is very pronounced due to which the performance of turbines located close to the ridge is mainly determined by the flow dynamics induced by the ridge and not by the wind turbine wakes. Thirdly, we find that there is an optimal turbine spacing, which maximizes the wind farm power output, for a wind farm located between two ridges. The reason is that wind turbines should not be placed too close to the hill, while they should also not be placed too close to each other. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L42.00002: Effect of complex terrains on wind energy production Abigayle Elaine Moser, Kaitlin Kelsey, Tae Hyung Kwon, Clarice Nelson, Percy Miguel Rueda Puelles, Luciano Castillo Access to electricity remains a challenge in mountainous regions due to difficulties in power grid interconnection. Wind turbines carry the opportunity to resolve the power deficit in remote areas; however, wind farm performance in complex terrain remains largely unknown. The potential to generate power in complex orographic conditions provides a greater economic benefit in the renewable energy sector. This study explores the viability of exploiting wind farms in the mountainous regions of Peru by investigating the impact of complex topographic characteristics on turbine wake recovery and power generation. In order to better understand the effect of the complex terrains, wind tunnel experiments were performed on a 1:290 scale model wind farm. To explore the advantages of complex topographic regions, scaled-down turbine in the model of Ollantaytambo region of Peru were used to analyze the wake effects through power output and particle image velocimetry (PIV). The results from the model wind farm over the complex terrain are indicative of greater efficiency in wind farms in terms of power output. Additionally, we will discuss the role of high-gradient surface slope on the energy entrainment and the vertical transport of momentum and kinetic energy over the model wind farm. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L42.00003: Optimizing turbine set-point distribution to mitigate effects of wind-farm induced gravity waves Luca Lanzilao, Johan Meyers Recently, it has been shown that flow blockage in large wind farms can lift up the top of the boundary layer, thereby triggering atmospheric gravity waves in the inversion layer and in the free atmosphere. These waves impose significant pressure gradients in the boundary layer causing detrimental consequences in terms of the farm’s efficiency. In the current study, we investigate the idea of controlling the wind-farm in order to mitigate the efficiency drop due to wind-farm induced gravity waves. The analysis is performed using a fast boundary layer model which divides the vertical structure of the atmosphere in three layers; the wind-farm drag force is applied over the whole wind-farm area and is directly proportional to the thrust set-point of the wind turbines. We implement an optimization model in order to derive the turbine thrust coefficient distribution that maximizes the wind-farm energy extraction. Interestingly, when the flow is sub-critical the optimal wind turbine thrust set-point assumes a sinusoidal behavior in the streamwise direction while it becomes a U-shaped curve when the flow is super-critical. Time-dependency effects are also investigated. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L42.00004: Effect of nocturnal low-level jet on wind farm performance Srinidhi Nagarada Gadde, Richard Stevens Large-eddy simulations of wind farms in a quasi-stationary, nocturnal, stable boundary layer are performed to understand the effect of the low-level jets (LLJ) on the farm performance. The effect of the LLJ is studied by systematically varying the cooling rate at the surface. The height of the boundary layer decreases with the increasing cooling rate and forms a LLJ due to the frictional decoupling at the inversion layer. We find that the power production of the wind farm increases with the cooling due to the high shear in the LLJ. For strong cooling, the destruction of turbulence by buoyancy causes a drop in the vertical entrainment; consequently, the turbines in the rear of the wind farm produce less power compared to the turbines operating in a low or moderately stable boundary layers. In addition to the power production, we analyse the flow structures to better understand the wind farm-boundary layer interaction in the highly stratified atmosphere. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L42.00005: Positive effect of a synthetic low-level jet on the mean power and momentum transport of a wind-turbine array Ali Doosttalab, Diego Siguenza, Jossy O'Donnell, Walter Gutierrez, Venkatesh Pulletikurthi, Yaqing Jin, Leonardo P. Chamorro, Luciano Castillo Nocturnal low-level jet (LLJ) is a distinctive phenomenon at the top of stable boundary layers. A low-level velocity peak results in attractive power resource for wind turbines. However, a maximum in the mean wind speed profile implies the co-existence of positive and negative mean shear in the vicinity of the peak. To gain better understanding of the impact of LLJ (e.g., positive \& negative shear) on the performance of a scaled-down power plant, with similar LLJ profile in the atmosphere were performed using particle imaging velocimetry (PIV). The results from single turbine and $3\times2$ turbines array in the positive and negative shear regions of the synthetic LLJ were compared to canonic turbulent boundary layer. For both positive and negative shear cases a 12\% increase in power generation in the $2^{nd}$ row were observed in comparison to the unstable boundary layer condition. In addition, the role of energy entrainment induced by the positive and negative shear of the LLJ and the contribution to the vertical transport of momentum and kinetic energy across the turbine array are explored in depth. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L42.00006: The low-level jet role on the mean power and momentum transport of vertical axis wind turbines Diego Siguenza, Ali Doosttalab, Humberto Bocanegra-Evans, Leonardo P. Chamorro, Luciano Castillo The stable temperature stratification at the lower part of the atmosphere causes a particular phenomenon known as low-level jet (LLJ) where its velocity peak results in attractive power resource for wind turbines. The positive and negative shear layers of the LLJ influences the wake recovery by encouraging the energy entrainment into the horizontal-axis wind farm canopy. To extend the knowledge of LLJ impact on wind farms, we aim to explore the effect of the LLJ on vertical-axis wind turbines (VAWT) in terms of its wake energy entrainment. The LLJ was synthetically generated in a wind tunnel to test different arrays of scaled-down VAWT where we measured the velocity fields downstream trough particle image velocimetry (PIV), and the power output of the turbines. We will discuss the role of the wake energy entrainment induced by the positive and negative shear in comparison with a regular unstable boundary layer scenario. [Preview Abstract] |
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