Sensitivity of rotor aeroelastic predictions with two-equation turbulence models

The capabilities of modeling complex rotor aeromechanics, principally via Computational Fluid Dynamics-Computational Structural Dynamics (CFD-CSD) coupling, have significantly improved with advances in computational hardware and software. Of particular interest is the accurate turbulence modeling for rotating blades, which remains one of the primary uncertainties in rotorcraft aeromechanics predictions. Recent collaborative investigations, where different solvers and turbulence models were applied, yielded dissimilar results for some flight conditions, but comparable results in others. An investigation of the behavior of two popular two-equation models for rotorcraft aeromechanics has been undertaken to understand their similarity and differences in various applications. The two models are based on the Kok and Menter variants of the k- \(\omega\) $\omega$ equations. The Kok model is evaluated with and without the Shear Stress Transport (SST) terms. The role of Delayed Detached Eddy Simulation (DDES) is also examined. These studies have been performed for rotating and non-rotating configurations, applying a common solver, mesh, and time step. Aerodynamic influences have been decoupled from aeroelastic applications to isolate causes of differences. The results indicate that differences arise when separated flows are present. The Kok model is unstable without the addition of a limiter on the production of the turbulent viscosity when a dynamic motion with large separation is modeled. Some of the aerodynamic differences in separated flows can be compensated for during fully trimmed aeroelastic predictions. Trim conditions arising from the use of different structural solvers or near dynamic stall conditions may introduce new variations.