Numerical Investigation of Droplet Impact Dynamics of Ammonium Dinitramide (Adn)-Based Liquid Propellant on Solid Surfaces

This study presents a numerical investigation of the impact dynamics of ammonium dinitramide (ADN)-based liquid green propellant droplet on non-heated solid surfaces with various surface roughness levels, using the volume of fluid (VOF) method. Droplet diameters of 2 mm and 4 mm with impact velocities of 1 m/s and 2 m/s were examined, corresponding to Weber numbers (We) of 56.77, 113.54, 227.09, and 454.17. Results reveal three distinct impact regimes: (i) capillary-dominated spreading and retraction at low We number, with max-spreading at 3.2; (ii) inertia-dominated, sustained lamella formation at moderate We value, with max-spreading at 4.3 and no retraction; and (iii) delayed capillary-driven retraction at high We number, with max-spreading up to 7. Surface roughness significantly influenced spreading at lower We values, where droplets on smoother surfaces achieved up to 8% larger maximum spreading compared to rough surfaces, while roughness effects diminished at higher We due to inertial dominance. No secondary droplet formation or splashing is observed, indicating that the liquid propellant's viscosity stabilizes the impact behavior. The results establish the first hydrodynamic baseline for ADN-based liquid droplet impact behavior, providing valuable critical information to injector design, splash-free deposition, and spray control in liquid propulsion systems.