Numerical analysis of noise reduction mechanisms on improved trailing edge serrations using the Lattice Boltzmann method

Abstract

This study investigates the flow topology and noise emission from an airfoil with combed teeth trailing edge geometry, to understand the noise reduction mechanisms observed in earlier experiments. A comparison is made to a straight trailing edge and a serrated trailing edge without combs. The different trailing edges are retrofitted to a NACA0018 airfoil at zero angle of attack. The flow field is analyzed by evaluating the fully explicit, transient, compressible Lattice Boltzmann equation. The acoustic far field is obtained by means of a Ffowcs-Williams and Hawkings integral solution. The simulated acoustic far field results and boundary layer characteristics for the teeth configuration match earlier experiments well. Furthermore, the numerical results confirm that the combed teeth give a larger noise reduction than the standard teeth. It is hypothesized that the main noise-suppression mechanism of the combs is an improvement in the streamline angles: in general, the flow tends to be less three-dimensional and more aligned with the serration edge. As a result, less vorticity is produced, especially at the root of the serrations.