Unsteady Aerodynamics of a Pitching Airfoil with Trailing-Edge Flap in a Four-Bladed Rotor Configuration

To improve the unsteady aerodynamic response of the IAR 330 PUMA rotor, the present analysis provides a two-dimensional (2D) CFD-based framework for rotor blade sections integrated with trailing-edge flaps (TEFs). From a biomimetic perspective, the TEF is treated as an engineering abstraction of the adaptive aft-chord and camber variation observed in natural flyers, providing a controlled morphing envelope for aerodynamic-load regulation. The scientific contribution consists of an integrated assessment of the NACA 13112 section over an extended TEF deflection range, the comparison of several relative TEF chord lengths, and the transfer of the section-level framework to a four-section representation of the IAR 330 PUMA rotor. First, the effect of TEF deflection on the trajectory and strength of the dynamic stall vortex (DSV) is examined for a pitching NACA 13112 airfoil with a chord length of c=0.6 m and a pitching axis located at x/c=0.25. The pitching motion was prescribed in ANSYS Fluent through a user-defined function (UDF), imposing a hysteresis variation of the angle of attack (AoA) from α=-3° to α=23°, while flap deflection angle (β) varied from β=-20° to β=8°, corresponding to upward and downward TEF deflection, respectively. The second part of this study extends the same pitching law to real-scale rotor blade sections under hovering flight conditions. For the rotor simulations, the Multiple Reference Frame (MRF) model was used for the steady-state analysis, whereas a Sliding Mesh interface was adopted for the transient computations. A 2D pressure-based solver was employed, together with the SST k-ω turbulence model, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) formulation, and a coupled pressure-velocity scheme. The rotational speed was set to ω=265 RPM, corresponding to a local tangential velocity of approximately U=145 m/s at the analysed radius of r=5.225 m and to a local Mach number of M≈0.43. The ideal-gas assumption and energy equation were employed to account for compressibility effects. Among the investigated IAR 330 PUMA rotor-section configurations, the TEF with a chord length of cf=0.25c TEF provided the most balanced aerodynamic response, reducing the peak pitching-moment coefficient by approximately 32% relative to the baseline airfoil.