Abstract:
Two transition modeling methods are assessed for predicting the skin frictions and flow field of a full-scale, hovering XV-15 tiltrotor using an unsteady Reynolds-averaged Navier-Stokes (RANS) flow solver. The rotor Figure of Merit (FM) is predicted over a range of collective pitch angles at two tip Mach numbers: a design tip Mach number of 0.69 and a reduced tip Mach number of 0.56. Computed skin frictions are compared with the measured data at selected collective pitch angles of 3°, 10°, 14° and 16.6°. The Langtry-Menter γ - Reθt transition model is integrated into Spalart-Allmaras's one-equation turbulence model (SA-TM) as well as Menter's shear stress transport two-equation turbulence model (SST-TM). Both SATM and SST-TM transition models are assessed for predicting the laminar separation-induced transition and the mid-chord flow separation phenomena on the XV-15 rotor. A method to correct premature flow separation is introduced to improve the model's behavior in predicting the hover performance and flow field for the XV-15 rotor at high thrust levels. Predicted skin frictions and hover performance show strong conformity with the wind tunnel measurements.