Effect of the Biomimetic Spine-Covered Protrusions (BSCPs) Height and Arrangement on SUBOFF Bare Hull Model Drag

The main aim of this work is to investigate the effect of the biomimetic spine-covered protrusions structure (BSCPs) inspired by pufferfish spines on the small autonomous underwater vehicles (AUVs) hull drag. The BSCPs with eight different heights (0.3–1 mm, 0.1 mm interval) and two arrangements (average and staggered arrays) are applied to a bare submarine hull (SUBOFF) at zero angle of pitch and yaw, and a plain hull is introduced for comparison. CFD-RANS method is used to simulate flow over the hull at a Reynolds number of 1.4 × 10⁶. The drag results show that the staggered arrays have the optimal drag reduction performance, with a maximum drag reduction of 9.47% for the BSCPs height of 0.3 mm. Although the hull pressure drag with BSCPs increases, the reduction in viscous drag is superior. Skin-friction coefficient reflects significantly lower BSCPs hull shear stress than plain hull. The reverse vortex prevents the ejection of low-velocity fluids and impedes sweeping of high-velocity fluids, effectively reducing the generation of Reynolds stresses near the wall. The combined reduction in shear and Reynolds stress leads to viscous drag decrease. The boundary layer developing downstream of the small-scale BSCPs has the more strong anti-separation ability. Furthermore, the BSCPs inhibit the vorticity motion, thereby hinders turbulent outbursts and reduces turbulence intensity. Future activities may involve the application of optimized BSCPs structure parameters on different AUVs hulls.