Investigation of Air Fluidization during Intruder Penetration in Sand

TL;DR

This study combines CFD-DEM simulations and experiments to explore how airflow influences sand penetration resistance, revealing nonlinear effects and four distinct stages of particle behavior during intrusion.

Contribution

It provides new insights into granular aeration mechanisms through integrated computational and experimental analysis, enhancing understanding of fluidization effects during sand penetration.

Findings

Penetration resistance decreases nonlinearly with depth under airflow.

Higher airflow rates increase the critical depth for effective fluidization.

Four stages of particle motion and channel formation during penetration are identified.

Abstract

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.