Investigation of Air Fluidization during Intruder Penetration in Sand

Self-burrowing robots navigating through granular media benefit from airflow-assisted burrowing, which reduces penetration resistance. However, the mechanisms underlying airflow-granular interactions remain poorly understood. To address this knowledge gap, we employ a coupled computational fluid dynamics and discrete element method (CFD-DEM) approach, supplemented by experimental cone penetration tests (CPT) under varying airflow conditions, to investigate the effects of aeration on penetration resistance. Experimental results reveal a nonlinear relationship between penetration resistance reduction and depth, wherein resistance approaches near-zero values up to a critical depth, beyond which the effectiveness of fluidization diminishes. Simulations demonstrate that higher airflow rates enhance the mobilization of overlying grains, increasing the critical depth. A detailed meso- and micro-scale analysis of particle motion, contact forces, and fluid pressure fields reveals four distinct penetration stages: particle ejection and channel formation, channel sealing, channel refill, and final compaction. These findings contribute to a deeper understanding of granular aeration mechanisms and their implications for geotechnical engineering, excavation technologies, and the development of self-burrowing robotic systems.