Wake structures and performances of wind turbine rotor with harmonic
surging motions under laminar and turbulent inflows
Abstract
Previous numerical studies suggested the motions of Floating Offshore
Wind Turbines (FOWTs) may enhance their wake recovery rates due to
having different modes of wake dynamics from the bottom-mounted
counterparts. However, the majority of previous research were conducted
with models having relatively low fidelities and/or focusing on laminar
inflow conditions. Models with lower fidelities are not able to capture
the dynamics of tip-vorticies reliably while inflow conditions without
turbulence are unrealistic out in the fields. In light of this, this
paper performed high fidelity numerical simulations (large eddy
simulation with actuator line technique) using full scale surging
(prescribed and harmonic) FOWT rotor with different inflow turbulence
intensities and multiple surging settings systematically to better
understand the wake dynamics of FOWT. The results showed that the
differences of wake structures between fixed and (harmonic) surging
rotors were pronounced when under laminar inflow conditions, where the
Surging Induced Periodic Coherent Structures (SIPCS) could be detected
straightforwardly; while the differences were much less significant when
under inflow conditions with realistic turbulence intensities, and the
SIPCS were clearly revealed only after phase-locked averaging. Moreover,
when under laminar inflow conditions, the values of mean disk-averaged
streamwise velocity at x/D=8 could be above 30% larger for the
surging cases than the fixed case, while the increases were down to
around 0 .5∼2% when under inflow conditions with realistic
turbulence intensities.