Effect of misaligned flow on trailing-edge noise

Abstract

This study presents the influence of misaligned flow on trailing-edge noise through high-fidelity large-eddy simulations, focusing on a NACA 0012 airfoil at a Reynolds number of $4\times 10^5$, a Mach number of 0.058, and a zero incidence angle. To model misaligned flow, the $30°$ and $45°$ swept airfoils are considered. Additionally, we simulate a straight airfoil with reduced Mach numbers equal to the chordwise velocity component of the swept airfoil, without spanwise flows. Numerical results are cross-examined with extended Amiet’s trailing-edge theory for a swept airfoil. It is found that the noise reduction trend with misaligned flow does not exactly correspond to the trend of reduced chordwise velocity. Our findings reveal that the presence of misaligned flow reduces the hydrodynamic wall-pressure spectrum near the trailing edge and generates destructive interference, efficiently mitigating airfoil noise; the latter has a more significant effect than the former. In particular, spanwise anti-phase coherent flow convection is found to be crucial for phase interference, which is not considered in the analytical approach. It is also found that the spanwise correlation length differs between numerical simulations and the generalized Corcos’ model, affecting the discrepancy in the level of noise reduction between numerical results and analytical results. As the acoustic behavior driven by flow misalignment in the swept airfoil represents a simplified flow pattern applicable to serrated geometries and straight blades undergoing the Coriolis effect in rotating motion, this work is anticipated to be instrumental in providing physical insights into practical applications.