| 17 Feb 2026
Experimental investigation of harmonic surge motions on the far wake of a wind turbine model and analysis of a resulting subharmonic wake response
Abstract. As the number of floating offshore wind farm projects grows across the world, several questions remain unanswered in the domain of floating wind turbine wakes. Previous studies observed that the motions impact the wake under laminar inflow conditions, and that the modifications are observable even under high turbulent inflow conditions, that are more realistic. However, these spatiotemporal behavior modifications still require precise characterization, especially under turbulent conditions. Thus, the present article aims to extend the previous work by studying the wake dynamics induced by surge motion under turbulent inflow, and to find the frequency and the spatiotemporal characteristics related to this motion. For this purpose, a porous disk is placed in a wind tunnel with a high level of turbulent inflow, and some experiments are performed at 8.125D (D the turbine diameter) downwind of the disk. First, hot-wire measurements are used to identify a 'critical' frequency at which wake dynamics are the greatest, and, then, stereo-PIV measurements are conducted for this frequency configuration to characterize the spatiotemporal wake dynamics. The results indicate a critical Strouhal number of approximately St = 0.24, for which the surge motion induces periodic contraction and expansion of the wake at the same frequency as the imposed motion. A quasi-steady-state analysis reveals that these modifications are larger than the predictions of basic wake models, highlighting the dynamic nature of the wake response. Moreover, inclined surge-generated periodic coherent structures are observed during this work, which are supposed to be related to shear effects. Additionally, an unexpected subharmonic frequency peak appears in the far wake velocity spectra. POD and coherence analyses suggest that this is related to a far wake meandering phenomenon, locked onto this subharmonic frequency.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Wind Energy Science.
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