NASA Dragonfly Mission: Coaxial Rotor Test and CFD Prediction

A fixed-pitch speed-controlled coaxial rotor system (Dragonfly Phase B*) was tested in the NASA Langley Transonic Dynamics Tunnel. The primary objective of the test was to experimentally measure rotor performance of a candidate full-scale flight rotor for the Dragonfly program, NASA's 4th New Frontiers Mission, in an atmosphere as close as possible to that on Saturn's largest moon, Titan. The heavy gas (R-134a) test setup provided Ma-scaled data at one-third chord-based Reynolds number when compared to Titan. These data serve as a validation anchor for computational fluid dynamics performance tables used by the Dragonfly team to predict rotor performance on Titan. The present work provides a thorough validation study of coaxial rotor performance estimation with an accuracy of order 5–10% over the primary flight envelope using an efficient hybrid blade element momentum theory with unsteady Reynolds-averaged Navier–Stokes (BEMT-URANS) flow solver, RotCFD. Airfoil lookup tables were generated in OVERFLOW. The computational performance matrix consisted of more than 1500 cases total, including hover, climb, edgewise flight, descent, and vortex ring state. Significant effort was devoted to quantitative comparisons between experimental data and computational results, with emphasis on uncertainty quantification and confidence levels of performance predictions. This work has been instrumental in establishing the hybrid BEMT-URANS methodology to provide mean coaxial rotor performance data for Dragonfly Mobility closed-loop simulations.