2025/03/27 by Bourhis, Martin, Messmer, Thomas, Hölling, Michael +1 · 4 citations
#FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn)
paper · doi:10.48550/arxiv.2503.21903
This study investigates how variations in freestream turbulence (FST) and the thrust coefficient (CT) influence wind turbine wakes. Wakes generated at CT ∈ \0.5, 0.7,0.9\ are exposed to turbulent inflows with varying FST intensity (1% \lesssim TI∞ \lesssim 11%) and integral length scale (0.1 \lesssim Lx/D \lesssim 2, D is the rotor diameter). For high-TI∞ inflows, a flow region within the wake is observed several diameters downstream, where a mean momentum deficit persists despite the turbulence intensity having already homogenised with the freestream, challenging traditional wake definitions. A ``turning point'' in the mean wake width evolution is identified, beyond which wakes spread at slower rates. Near-field (x/D \lesssim 7) wake growth rate increases with higher TI∞ and CT, while far-field (x/D \gtrsim 15) wake growth rate decreases with higher TI∞ -- a finding with profound implications for wind turbine wake modelling that also bridges the gap with entrainment behaviours observed in bluff and porous body wakes exposed to FST. Increasing Lx delays wake recovery onset and reduces the mean wake width, with minimal effect on the spreading rate. Both CT and FST influence high- and low-frequency wake dynamics, with varying contributions in the near and far fields. For low-TI∞ and small-Lx inflows, wake meandering is minimal, sensitive to CT, and appears to be triggered by shear layer instabilities. Wake meandering is enhanced for high-TI∞ and large-Lx inflows and is dominated by background turbulence. This emphasises the complex role of FST integral length scale: while increasing Lx amplifies meandering, it does not necessarily translate to larger mean wake width due to the concurrent suppression of entrainment rate.