Numerical study on benefits of curved serrations upon suppressing turbulent boundary layer trailing-edge noise

Abstract

Turbulent boundary layer trailing-edge noise can be effectively reduced by installing serrations on wind turbine blades. This study designs iron-shaped trailing-edge serrations with Bessel curves and investigates the noise reduction mechanism of three iron-shaped serrations (IS-0.25, IS-0.5, IS-0.75) with different curvatures installed on the NACA0018 airfoil using numerical methods. Large Eddy Simulation and Ffowcs-Williams and Hawkings acoustic analogy integral formula are employed to calculate the flow field and the far-field noise under Reynolds number $R_e=1.6\times {10}^5$. The results indicate that iron-shaped serrations achieve better aerodynamic performance and noise reduction compared to airfoils without serrations (Baseline) and with triangular serrations. IS-0.75 has the highest lift and lift-to-drag ratio at attack angles of $0^{\circ }$ to $8^{\circ }$. For attack angle $\alpha =6^{\circ }$, the fluid near the trailing edge of IS-0.75 adheres well to the airfoil surface, delaying flow separation and suppressing vortex shedding, with maximum low-to-moderate frequency noise reduction of 16.2 dB compared to Baseline.