Modeling of the fluid flow inside a crack of a substructure of an offshore wind turbine exposed to cyclic fatigue loading

• An enhanced analytical model has been developed to characterize the velocity field within a corrosion fatigue crack, and validated through (CFD) simulations. • Analytical and numerical analyses have demonstrated that, at extremely low Reynolds numbers, the velocity field of the crack is independent of the fluid properties. • Experimental observations from the literature indicate that the loading ratio significantly affects the corrosion rate due to the refreshing of the corrosive liquid inside the crack. This phenomenon is explained mathematically. This study presents a semi-analytical model to characterize fluid flow within narrow corrosion fatigue cracks, based on crack geometry and loading conditions. The model is validated through computational fluid dynamics simulations. Results show that the velocity field is explicitly dependent on the loading ratio R , while remaining insensitive to the loading amplitude and fluid properties, assuming that low Reynolds number conditions are fulfilled. Near the crack tip, the velocity magnitude approaches zero, whereas towards the crack mouth, the along-crack-length velocity component increases linearly and exhibits a parabolic distribution across the crack width. Furthermore, the model reveals that fatigue-induced crack face motion leads to periodic exchange of seawater within the crack, offering a mechanistic explanation for experimentally observed correlations between loading conditions and corrosion rates. The model describes how loading drives fluid flow within the crack, thereby refreshing the corrosive medium and governing its velocity under corrosion fatigue conditions.