NUMERICAL INVESTIGATION OF SURFACE SLIP ON TURBULENCE PROPAGATION AROUND THE TIP SECTION OF NREL 5MW OFFSHORE WIND TURBINE

Abstract

This study investigates the effect of surface slip on unsteady vortex dynamics around a NACA 64-618 airfoil at a Reynolds number of 1.3 × 10⁶ and angle of attack of 12°. A Navier-slip boundary condition, mimicking a superhydrophobic coating, was applied to evaluate its influence on turbulent flow behavior. Four slip lengths (Ls = 100 µm, 140 µm, 185 µm, and 400 µm) and a baseline no-slip case were analyzed. Instantaneous and mean velocity fields, frequency spectra, and proper orthogonal decomposition (POD) were used to characterize the flow. Slip was found to suppress trailing-edge separation bubbles and enhance wake flow acceleration. Shear-layer instability intensified, leading to early vortex roll-up. Frequency analysis showed a shift to lower dominant frequencies, especially for Ls = 400 µm, indicating small-scale vortex pairing. POD results revealed increased turbulent kinetic energy in the wake, concentrated within dominant mode pairs due to surface slip.