Reduction in Resistive Forces by Directional Air Fluidization in Dry Granular Media

Directional fluidization applies the concept of granular air fluidization to vary the resistive forces locally around an intruder in a granular medium. We fabricated a cylindrical intruder (d = 30mm, length = 30 mm) capable of blowing air through a nozzle at varying flow rates (from 0 to 100 L/min) and angles relative to the direction of intruder motion in dry granular media. Varying the flow rate and angle affects the drag force parallel to the intruder’s direction of motion as well as the lift force in the vertical direction. Drag experiments were performed by forcing the intruder horizontally with a robot arm at a low speed (v ~= 10 mm/s) in 5 cm of dry sand with grain diameters ranging from 0.4-0.8 mm. Multi-axis force data demonstrated a consistent reduction in saturated drag forces that was sensitive to air flow rate but insensitive to blowing angle (BL). Saturated lift forces showed a greater dependence on BL, with more significant reductions coinciding with steeper angles (60 - 90 degree range). These results suggest a scheme for minimizing resistive forces in lift and drag by blowing air downwards and open a door for growing robot navigation in granular media.