A STUDY OF THE EFFECTS AND SIGNIFICANCE OF TRANSITION MODELING FOR ROTORCRAFT APPLICATIONS

A four-blade helicopter rotor is modeled using computational fluid dynamics (CFD), and the impact on the flow-field with and without a floating fuselage geometry is assessed. The numerical predictions were made with CFD simulations using the NASA OVERFLOW 2.2n solver. For numerical simulations, the flow-field was discretized in a structured, overset topology with grids intended to solve the scope of the problem. Results based on a tip Mach number of 0.58 were acquired for various collective pitch angles. The simulations were completed with the Spalart-Allmaras (SA) one equation eddy-viscosity turbulence model along with the Spalart-Shur rotation/curvature correction coupled with the amplification factor transport (AFT) transition model. Additionally, Delayed, Detached Eddy Simulation (DDES) was used to induce hybrid RANS/LES behavior. Overall predicted figure of merit and laminar-to-turbulent transition patterns on the blade surfaces with and without the fuselage exhibited reasonable agreement with experimental data. Specifically, laminar-turbulent transition patterns on the blade surfaces at 10° collective pitch showed better agreement with experimental data than at 8° collective pitch. It was observed from the simulations that the blade root and tip vortex systems become increasingly unstable as the collective pitch is increased for both configurations.