Assessing intermittency characteristics via cumulant analysis of floating wind turbines wakes

Abstract

Turbulence intermittency in the wake behind a single floating wind turbine as well as merging wakes due to a pair of floating turbines is investigated using magnitude cumulant analysis and non-analytical cumulant analysis. This low-order statistical approach is used to compute the intermittency for its impact on fatigue loading and power output signals. In the near wake, a 60% increase in the intermittency coefficient compared to the inflow is found. Pitch motion causes a 17% increase in intermittency compared to fixed turbines. The pitch-induced intermittency depletes in the far-wake, and hence, investigating whether a pitch-induced intermittency of one turbine affects a successive one in a wind array setting is recommended. Non-local scale interactions near rotor tips are observed as undulations in the cumulant profiles, referred to as tip-effect fluctuations. The impact of turbulence intensity on intermittency is also examined, and a positive correlation between the two is found in the near-wake. In the far-wake, however, it is found to speed up the pitch-induced intermittency depletion. The wake merging region between two neighboring turbines experiences lower intermittency and damps tip-effect fluctuations. This work provides more reliable intermittency estimation by utilizing lower moment statistics. The findings aid description, turbulent loading quantification, and stochastic modeling for floating wind farm wakes as well as fixed ones for both single and merging wakes.