A numerical study on the airwake of a simplified ship using IDDES: Impact of aspect ratios

Artikel i vetenskaplig tidskrift, 2026

AbstractThe geometry of a ship plays a critical role in governing the bi-stable behaviour of its airwake. This study presents a comprehensive investigation into the influence of aspect ratio (Asp∗) on the wake bi-stability of a simplified ship model. Six aspect ratios, in the range Asp∗∈ [1.0, 2.0], were analysed using IDDES at Re = 8 × 104. The results reveal that flow separation at the hangar and the stern generates large recirculation regions, resulting in suction pressure effects that vary with aspect ratio. The aerodynamic drag peaks when aspect ratio is 1.15, while lift increases steadily with aspect ratio, reaching 11.3% when aspect ratio is 2. The evolution of lateral pressure gradients and switching dynamics shows that increased aspect ratio leads to reduced flow switching due to enhanced streamwise velocity near separation points. Reattachment lengths at both the superstructure and the wake region decrease with increased value of aspect ratio, coinciding with smaller vortex cores and increased turbulence. When aspect ratio is 1, stable transition regions are obtained at the top step, while symmetry is achieved at the bottom step. Consequently, an appropriate value of aspect ratio can potentially ensure improvement of wake flow dynamics for shipboard operational safety and energy efficiency.