Rod–airfoil configurations are commonly used to study turbulence–structure interaction noise, which is a major contributor to aerodynamic noise in various engineering applications. In this work, noise mitigation by regular and irregular leading-edge serrations is investigated for a rod–NACA0012–airfoil configuration using a direct hybrid CFD/CAA method. Large eddy simulations (LESs) are performed for the turbulent flow, and the acoustic perturbation equations (APEs) are solved to determine the acoustic field. The numerical results are validated by experimental data. The NACA0012 airfoil has different serrated leading edges, i.e., serrations with constant (regular) and varying (irregular) spanwise distributions of the amplitudes. Irregular spanwise amplitude distributions are generated by increasing or decreasing the amplitude of every second serration. The findings show an overall noise reduction for all configurations with regular and irregular serrations. The highest noise reductions are achieved by the irregular leading-edge serration configurations A3W2 and A6W2, with reductions of up to 11 dB in the Strouhal number range of $S_t$ = 0.25–0.75. Regular serration designs with greater amplitudes (A1W1 and A1W2) outperform other regular serration designs, reducing noise levels by up to 10 dB. For irregular configurations, the level of mitigation is found to be correlated with the base amplitude of their regular serrated counterparts.

The subsonic flows around NACA 0012 aerofoils with a solid, a porous, and a poro-serrated trailing edge (TE) at a Reynolds number of 1 × 10⁶ are investigated by a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) approach. The porosity is treated by the method-of-volume averaging. In the RANS, a two-equation low Reynolds number k-ε turbulence model is modified to include the porous treatment. Similarly the equations in the LES are extended by the Darcy–Forchheimer model. The simulation is set up with the broadband turbulent boundary layer trailing edge (TBL-TE) noise prediction as a future objective in mind, i.e., the noise sources in the trailing edge region are captured by the LES. To enforce a physically realistic transition from an averaged RANS solution towards a resolved turbulent flow field, at the inflow of the LES coherent structures are generated by means of the reformulated synthetic turbulence generation (RSTG) method. For the poro-serrated TE, turbulence statistics vary in the spanwise direction between the two extremes of a pure solid and a rectangular porous TE, where porosity locally increases the level of turbulence intensity and alters the near wall turbulence anisotropy.