| To investigate the reduction effect of air-jetting on the penetration resistance of objects moving in sandy soil, experimental studies were conducted to examine the influences of key factors such as airflow velocity, number and distribution of airflow outlets, and soil moisture content on horizontal penetration resistance, using the penetration test platform with adjustable functions of penetration speed and airflow velocity. The results with air-jetting were compared with the penetration resistance without air-jetting. The experimental results indicate that during jetting penetration in dry sand, only sand particles at and above the jet outlet’s position are dispersed by the airflow, while the lower particles are almost undisturbed. Under the influence of airflow, local fluidization of dry sand particles occurs, leading to a significant reduction in penetration resistance, with a more obvious effect at higher airflow velocity. For wet sand, air-jetting can also reduce the penetration resistance. Without air-jetting, the penetration resistance in dry sand linearly increases as moisture content in the range of 0 to 20%, while the increase of moisture content leads to an exponential growth in penetration resistance with air-jetting. In the experiments, the maximum drag reduction percentage for dry sand is 63.5%, and it is 35.5% for wet sand penetration with 20% moisture content. We kept the total air pressure as a constant and changed the number and distribution of jet outlets. The drag reduction percentage for dry sand is around 20%, while it is within 10% for wet sand. Optimal drag reduction is achieved with a single outlet jetting at the front of the intruder. It was noted that the influence of lateral jet outlets in dry sand caused a larger disturbance range than that of the single front outlet from the observation of the soil bed surface after penetration. In contrast, the wet sand bed fractured into several chunks, and under the influence of a single top jet outlet, a deep track pattern appeared on the surface. This experimental study provided theoretical support for reducing resistance and energy consumption in soil-contacting components and offered new insights for the optimization design of robots. |
