CFD Simulation of Soil Forces on a Flat Tillage Tool

Abstract

Soil forces on a tillage tool are of interest for several reasons, including the draft and power requirement to pull the implement. Pressure exerted by soil on the tillage tool and its distribution on tool surface with respect to tool wear is an important parameter for tool design with respect to the tool size and shape. The stress experienced by soil due to the tool motion is very important in identifying the soil mechanical behavior. The objective of this research was to gain an insight into soil forces and the pressure distribution on a simple tool considering the dynamics of soiltool interaction from fluid flow approach. Pressure distribution over the surface of a flat tillage tool, soil failure due to tool movement and draft requirement were investigated using computational fluid dynamics (CFD) for high speed tillage using a commercial CFD software CFX4.4. Soil was characterized as a Bingham material in its rheological behavior. Three dimensional simulations were conducted by control volume method with structured mesh. Results obtained from the simulations were compared with published data. Soil pressure on the tool surface increased with the tool operating speed. Pressure concentration was the highest at the tool tip; it decreased towards the soil surface and extended over greater area on the tool surface with increase in tool speed. Draft was related as a square function of speed. The longitudinal distance of the pressure bulb from the tool face(further most yield surface or conventionally, rupture distance) on the horizontal plane initially increased with speed and after a critical speed range of 4-6 m s-1, it did not increase with speed.