High-Fidelity Computations of the Prandtl-D Flying Wing

A complete, multi-fidelity numerical study is undertaken to investigate the loads and flow structure on the Prandtl-D, a low-speed flying-wing demonstrator designed to operate with a bell-shaped lift distribution. The Prandtl-D is simulated using Implicit Large-Eddy Simulation (ILES) at mean-chord Reynolds number (Rec) of 2.0x10^5 at the design condition of alpha = 8:0 to provide the full, three-dimensional unsteady flow topology. The flow-field at the wing’s design point was characterized by a laminar separation bubble that extended across the majority of the wing, open separation near the wingtip, and absence of a tip vortex. The flow structure over thewing contrastedwith previousRANS results at slightly higher Rec¯ but exhibited similarities with experiments at the same Rec. The wake sheet contained a vortical structure inboard of the wingtip that originated from the open-separation zone rather than the hypothesized downwash-upwash switch. Examination of loads and flow structure at different fidelities demonstrated favorable agreement between the ILES and RANS augmented by the AFT transition model, though inviscid method were a sufficient level of fidelity for engineering purposes to capture the net and sectional loads near the design condition as a means of developing fidelity thresholds for this nontraditional platform