Geometric design of confining lunar landing pads for plume-surface interaction mitigation: a comparative CFD study

Rocket exhaust impinging on the unconsolidated lunar regolith erodes the surface and ejects dust, sand and gravel at velocities that can exceed the lunar escape velocity, threatening nearby surface assets, orbiting hardware and the lander itself. This preprint presents a comparative computational fluid dynamics (CFD) study of five geometric concepts for a 50 m diameter confining lunar landing pad, named COOL-PAD (Confiner On-site Operational Landing PAD), sized for a Starship-class Human Landing System. Each concept combines a rounded central hill with a different arrangement of confiner walls (V-, R-, I-, C-shaped and curved "flower" walls) intended to slow down, redirect and raise the outgoing flow. Steady-state RANS simulations (SST k–ω) of a 9 m diameter CO₂ jet at 3,700 m/s, representing the combined exhaust of a multi-engine Raptor cluster, were performed with Cradle CFD scFLOW. The designs are compared in terms of peak surface pressure, peak wall shear stress, maximum outflow velocity and pad volume. Peak stagnation pressure was nearly insensitive to the wall layout (0.96–0.98 MPa), whereas peak wall shear stress (5.8–10.7 kPa) and maximum outflow velocity (100–251 m/s) varied strongly. The concept with a fully rounded hill and sixteen filleted V-shaped walls offered the best balance. The results suggest geometric design guidelines (early obstruction of the radial flow, wide flow-facing surfaces and rounded edges), valid as a relative comparison between designs given the simplified flow model. This work is derived from the author's Master's thesis in Space Engineering at Universidad Carlos III de Madrid (2024).