CFD Turbulence Transition Models Validation for Rotors in Unsteady Axial and Forward-flight Conditions using CREATETM-AV Helios

Abstract

Computational Fluid Dynamics (CFD) turbulence transition models are evaluated for rotors in unsteady axial and in forward flight conditions. The study is carried out using CREATETM -AV Helios with NASA codes, Overflow and FUN3D, as the near-body solvers. Three transition models are considered, Amplification Factor Transport (AFT), Langtry-Menter γ-Reθt (LM), and the LM with a crossflow transition model. The LM model is modified to allow for Galilean invariance. The validation study utilizes the data from two recent rotor tests where unsteady transition measurements were obtained on the upper (suction) surface of rotor blades using a novel application of the Differential Infrared Thermography (DIT) technique. The first configuration, the DLR RTG rotor, is a four-blade, 2.13-foot radius rotor in axial flow with pitching blades, operating at Reynolds numbers of 3.2 x 10-5 and 1.7 x 10-5> at three quarter radius, for the two test cases studied. The second configuration, the PSP rotor, is a model-scale, 5.58-foot radius, three-blade rotor in a high-advance-ratio, high-thrust forward flight condition, mounted on a ROBIN-Mod7 fuselage, and operating at a hover Reynolds number of 1.25 x 10-6 at three quarter radius. For this rotor, the validation study also included the DIT measurements on the lower (pressure) surface. Both configurations exhibit large unsteadiness in transition locations. CFD predictions are obtained using consistent grid resolution and numerical settings across the three models and the two rotor configurations. The computed results are analyzed in terms of the rotor transition maps, separation maps, and surface streamlines on the blade upper and lower surfaces. The agreement with the test data is good, in general, including the rapid, unsteady movement of the transition locations.