High Fidelity CFD Analyses of Dynamic Stall on a Four-Bladed Fully Articulated Rotor System

Accurate prediction of dynamic stall is one of the most challenging problems in rotorcraft modeling. The large majority of dynamic stall studies in the past, both computational and experimental, have investigated only airfoils and finite wings. Such studies do not take into account rotational effects and interactional aerodynamics that could impact the onset and evolution of dynamic stall. This study investigates dynamic stall on a four-bladed fully articulated rotor system. It evaluates the ability of state-of-the-art computational fluid dynamics (CFD) solvers to capture not only the unsteady and largely separated flows associated with dynamic stall but also rotational and interactional aerodynamics effects specific to rotorcraft. Experimental data for the study were taken from a 1991 experimental test in the ONERA S1MA transonic tunnel in Modane, France. High-fidelity computations were performed at the experimental conditions using CREATETM-AV Helios with NASA OVERFLOW and NASA FUN3D near-body solver modules, and elsA. In each of the solvers, high-resolution grids with various turbulence models were used to best capture the unsteady, highly separated flows associated with dynamic stall. Results from the study indicate that the ability of CFD to capture separated flow and dynamic stall depends on the origin of the separated flow. Separation and stall events from blade vortex interactions, as well as trim conditions with the rotors at incipient stall are much more difficult to capture than classic (high-angle-of-attack induced) dynamic stall.