###### Abstract  
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. a 202  
rod-airfoil configurations and concluded that radiated noise increases with a larger rod diameter and/or a shorter streamwise gap, owing to intensified vortex-structure interactions at the airfoil leading edge. Moreover, [PERSON] et al. [5] performed experimental and numerical investigations on sound generation from airfoil-flow interaction. They identified the interaction of vortices with the airfoil leading edge as the main characteristics of the rod-airfoil interaction flow and the dominant noise source. [PERSON] et al. [6] performed a numerical investigation on body-wake flow interaction over rod-airfoil configuration, contributing to the understanding of the aerodynamic noise characteristics of this configuration. The numerical investigation revealed that varying the distance between the rod and airfoil significantly influences the flow patterns and the suppression of turbulent fluctuations and noise radiation. Similarly, [PERSON] et al. [7] investigated the effect of rod diameter and rod-airfoil distance on noise generation using experimental and numerical techniques. They used low-dissipation upwind schemes and DDES, which showed reasonable agreement with experimental data. The application of serrations to the leading edge for noise mitigation has been investigated by several researchers. [PERSON] and [PERSON] [8] conducted a numerical analysis of aerodynamic noise mitigation via leading-edge serrations for a rod-airfoil configuration and provided insights into noise reduction using a wavy leading-edge design. The authors stated that leading-edge serrations reduced the unsteady loading on the airfoil and the coherence along the span, and did increase the spanwise phase variation. All these effects contribute to noise reduction. [PERSON] et al. [9] conducted experimental studies to examine the effects of wavy (serrated) leading edges on rod-airfoil interaction noise and found that serrated leading edges effectively reduced noise, with the sound power reduction level being influenced by both amplitude and wavelength. [PERSON] et al. [10] examined the broadband noise reduction effects of an airfoil with a serrated leading edge, finding that it effectively reduced noise at all angles without substantially altering noise directivity. Furthermore, the study conducted by [PERSON] et al. [11] investigated the impact of serrated leading edges on rod-airfoil interaction noise, revealing a significant reduction in noise levels across the mid- to high-frequency range.