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Title: Large-eddy simulations of wind-farm wake characteristics associated with a low-level jet

Abstract

Here, we performed a suite of flow simulations for a 12-wind-turbine array with varying inflow conditions and lateral spacings, and compared the impacts of the flow on velocity deficit and wake recovery. We imposed both laminar inflow and turbulent inflows, which contain turbulence for the Ekman layer and a low-level jet (LLJ) in the stable boundary layer. To solve the flow through the wind turbines and their wakes, we used a large-eddy simulation technique with an actuator-line method. We compared the time series for the velocity deficit at the first and rear columns to observe the temporal change in velocity deficit for the entire wind farm. The velocity deficit at the first column for LLJ inflow was similar to that for laminar inflow. However, the magnitude of velocity deficit at the rear columns for the case with LLJ inflow was 11.9% greater because of strong wake recovery, which was enhanced by the vertical flux of kinetic energy associated with the LLJ. In order to observe the spatial transition and characteristics of wake recovery, we performed statistical analyses of the velocity at different locations for both the laminar and LLJ inflows. These studies indicated that strong wake recovery was present, andmore » a kurtosis analysis showed that the probability density function for the streamwise velocity followed a Gaussian distribution. In a quadrant analysis of the Reynolds stress, we found that the ejection and sweep motions for the LLJ inflow case were greater than those for the laminar inflow case.« less

Authors:
 [1]; ORCiD logo [2];  [3]; ORCiD logo [2];  [1]; ORCiD logo [4]; ORCiD logo [1]
  1. Yonsei Univ., Seoul (South Korea). Dept. of Mechanical Engineering
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Earth and Environmental Science
  3. Korea Inst. of Atmospheric Prediction Systems, Seoul (South Korea)
  4. National Center for Atmospheric Research, Boulder, CO (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
Ministry of Trade, Industry, and Energy (MOTIE); National Research Foundation of Korea (NRF); USDOE
OSTI Identifier:
1411349
Report Number(s):
LA-UR-17-23268
Journal ID: ISSN 1095-4244
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Wind Energy
Additional Journal Information:
Journal Name: Wind Energy; Journal ID: ISSN 1095-4244
Publisher:
Wiley
Country of Publication:
United States
Language:
English
Subject:
17 WIND ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; actuator line method; low-level jet; velocity deficit; vertical flux of kinetic energy; wake recovery; wind farm

Citation Formats

Na, Ji Sung, Koo, Eunmo, Jin, Emilia Kyung, Linn, Rodman, Ko, Seung Chul, Muñoz-Esparza, Domingo, and Lee, Joon Sang. Large-eddy simulations of wind-farm wake characteristics associated with a low-level jet. United States: N. p., 2017. Web. doi:10.1002/we.2152.
Na, Ji Sung, Koo, Eunmo, Jin, Emilia Kyung, Linn, Rodman, Ko, Seung Chul, Muñoz-Esparza, Domingo, & Lee, Joon Sang. Large-eddy simulations of wind-farm wake characteristics associated with a low-level jet. United States. doi:10.1002/we.2152.
Na, Ji Sung, Koo, Eunmo, Jin, Emilia Kyung, Linn, Rodman, Ko, Seung Chul, Muñoz-Esparza, Domingo, and Lee, Joon Sang. 2017. "Large-eddy simulations of wind-farm wake characteristics associated with a low-level jet". United States. doi:10.1002/we.2152.
@article{osti_1411349,
title = {Large-eddy simulations of wind-farm wake characteristics associated with a low-level jet},
author = {Na, Ji Sung and Koo, Eunmo and Jin, Emilia Kyung and Linn, Rodman and Ko, Seung Chul and Muñoz-Esparza, Domingo and Lee, Joon Sang},
abstractNote = {Here, we performed a suite of flow simulations for a 12-wind-turbine array with varying inflow conditions and lateral spacings, and compared the impacts of the flow on velocity deficit and wake recovery. We imposed both laminar inflow and turbulent inflows, which contain turbulence for the Ekman layer and a low-level jet (LLJ) in the stable boundary layer. To solve the flow through the wind turbines and their wakes, we used a large-eddy simulation technique with an actuator-line method. We compared the time series for the velocity deficit at the first and rear columns to observe the temporal change in velocity deficit for the entire wind farm. The velocity deficit at the first column for LLJ inflow was similar to that for laminar inflow. However, the magnitude of velocity deficit at the rear columns for the case with LLJ inflow was 11.9% greater because of strong wake recovery, which was enhanced by the vertical flux of kinetic energy associated with the LLJ. In order to observe the spatial transition and characteristics of wake recovery, we performed statistical analyses of the velocity at different locations for both the laminar and LLJ inflows. These studies indicated that strong wake recovery was present, and a kurtosis analysis showed that the probability density function for the streamwise velocity followed a Gaussian distribution. In a quadrant analysis of the Reynolds stress, we found that the ejection and sweep motions for the LLJ inflow case were greater than those for the laminar inflow case.},
doi = {10.1002/we.2152},
journal = {Wind Energy},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}

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  • In this study, wind turbine impacts on the atmospheric flow are investigated using data from the Crop Wind Energy Experiment (CWEX-11) and large-eddy simulations (LESs) utilizing a generalized actuator disk (GAD) wind turbine model. CWEX-11 employed velocity-azimuth display (VAD) data from two Doppler lidar systems to sample vertical profiles of flow parameters across the rotor depth both upstream and in the wake of an operating 1.5 MW wind turbine. Lidar and surface observations obtained during four days of July 2011 are analyzed to characterize the turbine impacts on wind speed and flow variability, and to examine the sensitivity of thesemore » changes to atmospheric stability. Significant velocity deficits (VD) are observed at the downstream location during both convective and stable portions of four diurnal cycles, with large, sustained deficits occurring during stable conditions. Variances of the streamwise velocity component, σ u, likewise show large increases downstream during both stable and unstable conditions, with stable conditions supporting sustained small increases of σ u , while convective conditions featured both larger magnitudes and increased variability, due to the large coherent structures in the background flow. Two representative case studies, one stable and one convective, are simulated using LES with a GAD model at 6 m resolution to evaluate the compatibility of the simulation framework with validation using vertically profiling lidar data in the near wake region. Virtual lidars were employed to sample the simulated flow field in a manner consistent with the VAD technique. Simulations reasonably reproduced aggregated wake VD characteristics, albeit with smaller magnitudes than observed, while σu values in the wake are more significantly underestimated. The results illuminate the limitations of using a GAD in combination with coarse model resolution in the simulation of near wake physics, and validation thereof using VAD data.« less
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