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.

When the wind turbine operates in the wind-sand environment, the sand particles will cause erosion and wear on the surface of the wind turbine blades, which will result in morphological changes and lead to changes in aerodynamic performance. In order to deeply understand the degree of wear of wind turbine blades in the wind-sand environment and its change rule with time, and to provide scientific basis for the operation and maintenance of wind turbines in the wind-sand environment, it is necessary to systematically study the dynamic evolution process of erosion and wear on the surface of the blades, as well as the change of the aerodynamic performance in this process. This study adopts the numerical model of flow-solid-erosion coupling, based on the particle concentration-time conversion method, and by simulating the erosion process of wind-sand on the wind turbine-specific airfoil S809, the dynamic evolution process of the morphology of the airfoil surface under the erosion effect of the sand particles is explored, and the depth of erosion and morphology of the airfoil surface are analyzed, and the influence law of the wind-sand particles on the morphology and its aerodynamic performance of the airfoil surface of the S809 are further investigated under different angles of attack. The influence of sand particles on the surface morphology of S809 airfoil at different angles of attack is further investigated. The study shows that, with the advancement of erosion time, the abrasion degree of sand particles on the airfoil surface increases, which makes the depth of the erosion pits deepen, and the pressure coefficient fluctuation of the airfoil surface becomes drastic. At the same time, the lift coefficient shows a trend of slight increase and then slow decrease. The particle erosion and wear were concentrated mainly in the high-pressure areas of pressure surface at the leading edge of airfoil segment. The wear area of airfoil segment was gradually enlarged with the increase of the erosion time, and the depth of wear was deepened. There was the slightly decrease rate of the maximum depth after the surface erosion of airfoil segment. The area of suction surface erosion wear was shifted to the leading edge, with the increase of angle of attack. While the area of pressure surface erosion wear was to the trailing edge. The larger the angle of attack was, the more serious the erosion wear in the region of the pressure front edge of the airfoil segment was. At the same time, the pressure coefficient of the wing section cross-section was appeared the fluctuation in the process of erosion. The more outstanding fluctuation was found with the advancement of the erosion time, especially on the more significant fluctuation of the pressure coefficient at the front edge of the suction force. Overall, the wing segment lift coefficient showed the increasing first and then decreasing in the process of particle erosion, with the advancement of erosion time. Once the angle of attack was 10° and the erosion duration was 40 h, the wing segment lift coefficient increased up to 6.3% than before. When the angle of attack was more than 12°, the coefficient of lift decreased significantly after 20 h of erosion, compared with the low angle of attack. The value of β was about 0.62 at the angle of attack from 2° to 8°, whereas, the value of β increased up to 0.82 at the angle of attack of 10°. The slow increase was observed with the increase of the angle of attack. In general, the wing segment lift-to-drag ratio was depended mainly on the incoming wind and sand at small angles of attack. There was no influence under the incoming wind and sand at large angles of attack. The findings can provide the data support and theoretical basis to maintain and repair the wind turbines in the wind-sand inflow environment.