Numerical modelling of soil stress and pressure distribution on a flat tillage tool using computational fluid dynamics

Soil pressure on tillage tools and its distribution over the tool surface are important factors for tool design with respect to tool wear. Soil stresses due to the tool motion are also very important in identifying the soil mechanical behaviour. The pressure distribution over the surface of a flat tillage tool and the soil stress pattern due to forward motion of the tool were investigated using computational fluid dynamics (CFD) simulations for high-speed tillage. The soil was characterized for its rheological behaviour as a Bingham material. Three-dimensional analyses were carried out by the control volume method with structured mesh using CFX4.4, a commercial CFD code. The results indicated that soil stress due to the tool motion was distributed as a set of pressure bulbs with maximum stress near the tool face that was decreasing along the longitudinal direction. Higher tool speed was accompanied by an increase in soil stress in front of the tool. Soil stress close to the tool tip increased from 220 to 1060 kPa, while the maximum pressure on the tool surface increased from 250 to 1240 kPa when the tool speed was increased from 1 to 10 m s−1. A critical speed range of 4–6 m s−1 was found after which increase in tool speed was accompanied by a decreasing trend of the longitudinal distance of soil failure zone from the tool face. Soil pressure on the tool surface and the resulting draught predicted by CFD modelling were very close when compared to published data based on finite element analysis on similar studies.