Numerical investigation on the influence of a spoiler structure for local scour protection

As a Marine structure, monopile foundations can significantly change the hydrodynamic conditions around the piles, leading to local scour. The main causes of local scour around monopile foundations are horseshoe vortex, downward flow, and wake vortex. In this study, a large-diameter monopile foundation of offshore wind power is taken as the research object. A novel spoiler structure is proposed and a three-dimensional numerical model is established. Based on numerical simulation, the influence mechanism of spoiler structure on local scour around monopile is investigated in constant current. The influence of length L and height H2 of the spoiler on the location and strength of local horseshoe vortex is discussed, and the distribution characteristics of the bed shear stress are obtained. By comparing the distribution of local horseshoe vortex and bed shear stress with and without spoiler, it is found that the spoiler ribs can significantly reduce the strength of horseshoe vortex and the regional shear stress between ribs. The local horseshoe vortex presents three flow mechanisms under different geometric spoiler structures, namely independent horseshoe vortex, disturbed horseshoe vortex, and separated horseshoe vortex. In the three horseshoe vortex states, the protected bed area has a linear relationship with the spoiler geometric length or height. Additionally, the spoiler exhibits good scour protection characteristics with L/ H2=1. By analyzing the flow field characteristics around the spoiler, the influence mechanism of ribs on the horseshoe vortex and shear stress distribution around the monopile foundation is revealed. Overall, the novel spoiler structure shows promising results for local erosion protection, and it has practical importance for guiding the protection design of monopile foundations.