A Numerical Study of In-Ground Effect Aerodynamics and Sediment Entrainment for the Dragonfly Lander

NASA's Dragonfly rotorcraft will perform repeated low altitude operations during takeoff, landing, and hover on Titan, where rotor downwash interacts strongly with the surface. This study uses computational fluid dynamics under Titan atmospheric conditions to quantify the influence of ground proximity on rotor performance, fuselage loading, and wall shear stress (WSS) for the Dragonfly lander. Simulations spanning out-of-ground effect (OGE) to strong in-ground effect (IGE) show increasing thrust augmentation and growing unsteadiness as the vehicle descends below h/D = 1. The resulting recirculation beneath the fuselage produces notable fluctuations in the vertical and longitudinal loads. WSS rises sharply near h/D = 0.65, forming localized regions of high shear driven by the confined downwash and redirected upwash. These conditions represent the most favorable regime for sustained sand and dust mobilization on Titan, while touchdown and subsequent hold reduce the shear as the flow stabilizes. The results define the near surface aerodynamic environment relevant to Dragonfly's flight safety, sensor performance, and surface interaction risk during descent and landing.