Numerical Investigation of Unsteady Boundary Layer Transition on a Dynamically Pitching Rotor

Predictions of unsteady boundary layer transition are performed on a four-bladed rotor in axial inflow using a computational fluid dynamics approach. The configuration is based on experiments performed at the German Aerospace Center (DLR) in the 1.6-m × 3.4-m wind tunnel in the rotor test facility (RTG). Simulations are performed using the NASA OVERFLOW 2.3 solver with hybrid RANS/LES and laminar turbulent transition modeling. Solutions are based on a hover tip Mach number of 0.143 with prescribed cyclic pitching conditions. Computational methods and grid generation are described. The rotor flow field is analyzed, and the effect of transition modeling on unsteady boundary layer transition prediction is assessed. Laminar-turbulent transition predictions and rotor performance are compared to experimental measurements obtained at the DLR RTG. A study of sensitivity was performed on freestream turbulence intensity to investigate its effect on predicted rotor transition.