Investigating the Physical Mechanisms that Modify Wind Plant Blockage in Stable Boundary Layers

Miguel Sanchez Gomez, Julie Lundquist, Jeffrey Mirocha, Robert Arthur

Research output: Contribution to journalArticlepeer-review

2 Scopus Citations

Abstract

Wind plants slow down the approaching wind, a phenomenon known as blockage. Wind plant blockage undermines turbine performance for front-row turbines and potentially for turbines deeper into the array. We use large-eddy simulations to characterize blockage upstream of a finite-size wind plant in flat terrain for different atmospheric stability conditions and investigate the physical mechanisms modifying the flow upstream of the turbines. To examine the influence of atmospheric stability, we compare simulations of two stably stratified boundary layers using the Weather Research and Forecasting model in large-eddy simulation mode, representing wind turbines using the generalized actuator disk approach. For a wind plant, a faster cooling rate at the surface, which produces stronger stably stratified flow in the boundary layer, amplifies blockage. As a novelty, we investigate the physical mechanisms amplifying blockage by evaluating the different terms in the momentum conservation equation within the turbine rotor layer. The velocity deceleration upstream of a wind plant is caused by an adverse pressure gradient and momentum advection out of the turbine rotor layer. The cumulative deceleration of the flow upstream of the front-row turbines instigates vertical motions. The horizontal flow is diverted vertically, reducing momentum availability in the turbine rotor layer. Although the adverse pressure gradient upstream of the wind plant remains unchanged with atmospheric stability, vertical advection of horizontal momentum is amplified in the more strongly stable boundary layer, mainly by larger shear of the horizontal velocity, thus increasing the blockage effect.
Original languageAmerican English
Pages (from-to)1049-1069
Number of pages21
JournalWind Energy Science
Volume8
Issue number7
DOIs
StatePublished - 2023

NREL Publication Number

  • NREL/JA-5000-87581

Keywords

  • atmospheric stability
  • large-eddy simulations
  • turbine performance
  • wind plant blockage

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