Deterministic and statistical analysis of trailing-edge noise mechanisms with and without serrations

The scope of this paper is to perform a detailed analysis of the unsteady flow properties in proximity of the trailing-edge of a lifting free transition NACA 64-618 extruded airfoil. The natural transition cases 6 and 7 of the AIAA workshop on Benchmark Problems for Airframe Noise Computations (BANC-V Category 1) are considered as references. The numerical flow solution is carried out by using the fully explicit, transient and compressible lattice-Boltzmann equation implemented in the CFD/CAA solver Exa PowerFLOWR. The acoustic far-field is obtained by using the Ffowcs-Williams and Hawking integral solution applied to the wing surface. In addition, the validity of Roger and Moreau's trailing- edge model, fed with Schlinker-Amiet's and Rozenberg's wall-pressure spectrum model, is checked by comparison with both experimental and numerical results. The influence of the computational grid on the turbulent boundary layer statistics at the trailing-edge is documented as well. As conclusive effort, the effectiveness of sawtooth serrations on noise reduction is investigated by considering two different flap angles at a fixed airfoil incidence.