CFD-based Aerodynamic Analysis of Wavy-Surface Ellipsoidal Seed Capsules Launched from an Unmanned Aerial Vehicle-based Forest-Planting System

Unmanned aerial vehicle (UAV)-based aerial seeding has emerged as a cost-effective approach for forest restoration, particularly in remote and inaccessible terrains. Its practical effectiveness remains constrained by low seeding accuracy and uneven dispersal. These issues are largely driven by aerodynamics of nonspherical surfaced seeds that remains unexplored. This study addresses this gap through the computational fluid dynamics (CFD) investigation of wavy-surface ellipsoidal seed capsules during the early phase of their launch from a pneumatic gun. Three-dimensional simulations are performed for 10³ ≤ Re ≤ 5 × 10⁴ and α = 0°-90°, considering parametric variations in waviness parameters. Grid and time-step independence tests, as well as a confinement test of the computational domain, are carried out. The CFD verification and validation show that the SST k-ω model is the best choice, with a maximum deviation of 6.5% from the empirical correlation. The results reveals that aerodynamics of the capsules becomes sensitive to waviness at α = 60° and within the range log₁₀Re = 3.7-4.6. As the amplitude A* increases from 0 to 1, at log₁₀Re = 4.3 and α = 60°, the drag coefficient C D , lift coefficient C L , and pitching moment coefficient C M vary from 0.46 to 0.60, from 0.24 to 0.47, and from -5.8 × 10 -2 to -8.1 × 10 -2 , respectively. As the wavelength λ* increases from 0.5 to 1, C D , C L , and C M vary from 0.49 to 0.58, from 0.29 to 0.47, and from -6.2 × 10 -2 to -7.6 × 10 -2 , respectively. Flow-field analysis indicates that the waviness parameters alter the pressure distribution and vortex structure in the wake.