Abstract: A bio-inspired wavy surface was presented for the wind turbine airfoil in a sand-laden environment. A numerical investigation was also made to explore the effects of the bio-inspired wavy surface and passive flow on the erosion resistance and aerodynamic performance of wind turbine airfoils. The primary relationship was then established for the effects of the geometric parameters of the wavy structure on the sand particle impacts and aerodynamic forces. An optimal design was achieved to balance between high aerodynamic efficiency and robust protection against solid particle erosion. The S809 airfoil was selected as the commonly used profile in wind turbine applications. A computational framework was used to conduct using the Reynolds-Averaged Navier-Stokes (RANS) equations. The steady-state turbulent flow field was obtained around the airfoil. The Lagrangian-based Discrete Phase Model (DPM) was coupled with the fluid dynamics solver in order to simulate the erosive environment. The trajectories of individual sand particles were tracked to determine their impact velocities, angles, and positions on the airfoil surface. This one-way coupled approach was used to accurately capture the dilute particle flows of the aeolian sand transport. Four geometric variables were examined to systematically parameterize the wavy surface: the starting position of the wavy section on the airfoil chord, the total coverage length, wavelength, and amplitude. The results demonstrated that the highly effective strategy was achieved in the wavy structure on the airfoil's pressure surface, in order to mitigate the erosion damage. The enhanced protection was attributed to the underlying physical mechanism. Specifically, the stable and local recirculation vortices were generated within the troughs of the waves. An "aerodynamic shielding" was then created to alter the near-wall flow field. Among them, a significant fraction of the incoming sand particles was deflected away from the airfoil surface, thus reducing the overall rate and kinetic energy of impacts. There was a critical trade-off between the gains in the erosion resistance and the aerodynamic penalties. It was found that the specific geometry of the wavy surface had a decisive impact on the integrated performance of airfoils. The installation position was also proved as the foundational parameter to balance the performance; The wavy structure was initiated at 10% of the chord length from the leading edge on the pressure side. A beneficial baseline was established for the erosion reduction across all tested angles of attack without severely compromising the critical aerodynamics of the leading-edge region. Furthermore, a cost-benefit relationship was observed concerning the coverage length of the wavy section. While the longer sections offered more extensive surface protection, a notable aerodynamic penalty was also induced to reduce the pressure on the pressure surface. Consequently, the airfoil's lift-to-drag ratio was lowered, especially at the low angles of attack. A weighted optimization analysis showed that an optimal design was identified to consider both erosion mitigation and aerodynamic efficiency. A wavy structure was applied to the pressure surface that commenced at 10% of the chord length and extended for a total length of 35.6% of the chord. This configuration was provided for the most favorable balance. The micro-geometry of this optimal structure was characterized by a short wavelength of 4 mm and a relatively small amplitude equal to 20% of its wavelength. This specific combination was highly effective in inducing the protective vortices and then minimizing the additional dragging. The bio-inspired concept was confirmed to provide a concrete and quantifiable design. The findings can offer passive protection for the next-generation and high-durability wind turbine blades. The blade service life can also be extended to reduce the operational and maintenance costs in the sand-rich regions.