Unveiling the Unsteadiness: Modeling Dragonfly's Descent With an Aerodynamic Trajectory Framework

This paper presents the development of an unsteady Computational Fluid Dynamics (CFD) workflow to simulate the trajectory of the Dragonfly lander through the Titan atmosphere following several distinct prescribed trajectories computed by flight dynamics software tools such as Closed Loop Simulation (CLS) and Program to Optimize Simulated Trajectories II (POST II). The purpose of these unsteady trajectories is to assess the effects of transient dynamic motion and oscillations, specifically non-zero angular rates, on the aerodynamic loads imparted on the lander body as compared to a quasi-steady approach where loads are solely dependent on the current flight velocity and rotor speeds. The quasi-steady loads are based on a Reynolds-Averaged Navier-Stokes (RANS) simulation approach which was then compared with time-accurate Improved Delayed Detached Eddy Simulations (IDDES). In all cases, the rotors were simulated using a “Virtual Disk Model (VDM)” based on Blade Element Momentum Theory (BEMT) coupled to the CFD solution. Both simplified comparison cases with prescribed constant angular rates as well as full trajectories of lander flight paths from complete flight dynamics simulations of the Preparation for Powered Flight (PPF) phase and the lander’s first flight are shown. The results demonstrate overall good agreement between the flight dynamics simulation results (which themselves are informed by a CFD generated database using the RANS approach) and the unsteady CFD simulations, though additional higher frequency content and noisier signals are noted in the unsteady CFD.