Investigation of the near-wake behaviour of a utility-scale wind turbine

TL;DR

This study uses advanced flow visualization techniques to analyze the complex three-dimensional near-wake behavior of a large wind turbine, revealing how operational changes influence wake dynamics and turbulence.

Contribution

It provides detailed three-dimensional near-wake data including effects of the tower and hub, and links wake behavior to turbine operational parameters, enhancing wake modeling and control strategies.

Findings

High-speed flow region behind the hub identified

Turbulence is enhanced by the hub and reduced by the tower

Wake expansion varies with turbine operation

Abstract

Super-large-scale particle image velocimetry and flow visualization with natural snowfall is used to collect and analyze multiple datasets in the near wake of a 2.5 MW wind turbine. Each dataset captures the full vertical span of the wake from a different perspective. Together, these datasets compose a three-dimensional picture of the near-wake flow, including the effect of the tower and hub and the variation of instantaneous wake expansion in response to changes in turbine operation. A region of high-speed flow is observed directly behind the hub, and a region of low-speed flow appears behind the tower. Additionally, the hub produces a region of enhanced turbulence in its wake while the tower reduces turbulence near the ground as it breaks up turbulent structures in the boundary layer. Analysis of the instantaneous wake behaviour reveals variations in wake expansion, and even periods of wake contraction, occurring in response to changes in the angle of attack and blade pitch gradient. This behaviour is found to depend on the region of operation of the turbine. These findings can be incorporated into wake models and advanced control algorithms for wind farm optimization and can be used to validate wind turbine wake simulations.