The effects of leading edge radius on the static and dynamic stall characteristics of rotor airfoils are investigated. Initially, a parametric airfoil (PARFOIL) method is employed to generate four morphed airfoils with different leading edge radii based on a NACA 0012 airfoil. Subsequently, the Reynolds-averaged Navier–Stokes (RANS) method is employed to simulate the aerodynamic characteristics of static airfoils, while the improved delayed detached-eddy simulation (IDDES) method is employed for pitching airfoils. The effectiveness and accuracy of the computational fluid dynamics (CFD) methods are demonstrated through favorable agreement between the numerical and experimental results. Finally, both the static and dynamic aerodynamic characteristics are simulated and analyzed for the airfoils with varying leading edge radii. Comparative analyses indicate that at low Mach numbers, the high adverse pressure gradient near the leading edge is the primary cause of leading edge separation and stall. A larger leading edge radius helps to reduce the suction pressure peak and adverse pressure gradients, thus delaying the leading edge separation and stall of airfoil. At high Mach numbers, the leading edge separation and stall are mainly induced by the shock wave. Variations in leading edge radius have minimal impacts on the high adverse pressure gradient induced by the shock wave, thus making the stall characteristics of airfoils almost unaffected at high Mach numbers.

This study investigates dynamic stall mechanisms of a pitching NACA 0012 airfoil through high-fidelity computational fluid dynamics (CFD) simulations. The improved delayed detached eddy simulation (IDDES) method based on a sliding mesh system is constructed and validated against experimental airload measurements. The results demonstrate a good agreement and the capability to capture three-dimensional flow structures. Comparative analyses at two Mach numbers of 0.283 and 0.5 reveal distinct stall physics. At the Mach number of 0.283, a notable 9.7° delay is observed between the static and dynamic stall. The airfoil experiences a leading-edge stall dominated by a strong adverse pressure gradient and generates rapid airload variations. In addition, trailing-edge vortex (TEV) and secondary leading-edge vortices (LEVs) induce distinct airload fluctuations. After the shedding of primary vortices, secondary vortices develop. In contrast, the airfoil at the Mach number of 0.5 presents a reduced stall delay of 6.4° and a shock-induced dynamic stall characterized by dispersed, smaller vortices, which results in mild airload variations during stall. Aerodynamic damping analysis identifies stall delay as a primary contributor to negative damping. Enhanced pitching stability at the higher Mach number correlates with reduced stall delay and different LEV development characteristics. Results across varying reduced frequencies show that increasing reduced frequency delays the aerodynamic response and stall onset. At Ma = 0.283, this increasement promotes a divergent tendency in pitching motion, whereas at Ma = 0.5, it induces greater oscillatory stability attributed to distinct stall characteristics.

To investigate the vortex dynamics and loading noise radiation characteristics during dynamic stall of helicopter rotor airfoils, a numerical study is carried out using the unsteady Reynolds-averaged Navier–Stokes method and the Ffowcs Williams-Hawkings equation. First, the aerodynamic and aeroacoustic characteristics of NACA0012 airfoil in dynamic stall were calculated. The numerical method is validated through comparisons with experimental data. Then, the aeroacoustic characteristic of an airfoil in the typical deep stall condition is analyzed, with a detailed discussion on the relationship between flow phenomena and sound pressure (SP). Based on the vortex evolution over airfoil surface, a model for loading noise driven by vortex evolution during dynamic stall is presented. Finally, the impact of reduced frequency (k) on the loading noise characteristics of the airfoil is analyzed, and conclusions are obtained. The dynamic stall loading noise is primarily caused by the shedding and movement of the dynamic stall vortex (DSV) and trailing edge vortex, with DSV shedding inducing rapid and intense SP fluctuations, resulting in high-intensity noise of up to approximately 30 Pa. An increase in k enhances the rate of change in unsteady surface pressure coefficient (Cp), which accelerates pressure variation and leads to a significant rise in overall sound pressure level.