Abstract: Dynamic stall affects the aerodynamic characteristics of rotor airfoils. The aerodynamic performance of helicopter rotors is restricted by dynamic stall. A deeper understanding of its underlying mechanisms will facilitate the aerodynamic optimization of rotor airfoils designs. This study establishes a numerical simulation framework for rotor airfoils dynamic stall using a Delayed Detached Eddy Simulation (DDES) and \gamma \text-\overline\mathrmRe_\theta t coupled model (TDDES) developed by our group. The TDDES model accurately simulates unsteady aerodynamics, as validated through NACA0012 airfoil cases. To reveal the influence of aerodynamic parameters (Mach number, mean angle of attack, angle-of-attack amplitude, reduced frequency, leading edge radius, maximum thickness, maximum camber) on unsteady dynamic stall, we perform unsteady numerical simulations based on the TDDES model using the OA309 airfoil. The variation characteristics of aerodynamic coefficients and flow-field structures are analyzed under controlled parameter variations. Comparative analysis of computational results reveals that an increase in Mach number causes dynamic stall vortex (DSV) to rupture earlier and dissipate more rapidly, manifesting as a decreased stall angle of attack and a reduced negative peak in the pitching moment coefficient. Increases in the mean angle of attack and its amplitude lead to a higher stall angle of attack and a significantly larger negative peak in the pitching moment coefficient. A higher reduced frequency results in a more pronounced delay in the dynamic stall process, retarding the separation of the DSV and allowing the separation vortex to accumulate greater strength, thereby enhancing the hysteresis effect of the aerodynamic forces. Increasing the leading-edge radius weakens the adverse pressure gradient near the airfoil's leading edge, suppressing the intensity of the separation vortex and consequently alleviating the severity of dynamic stall. Enlarging the airfoil's maximum thickness and maximum camber promotes airflow attachment by altering the geometric shape of the airfoil, which can effectively suppress the occurrence of dynamic stall. The research results can provide a theoretical basis and data support for the unsteady aerodynamic design and dynamic stall suppression of helicopter rotor airfoils.