Impact forces on the drive spoon of a large cannon irrigation sprinkler: Simple theory, CFD numerical simulation and validation

The service life and stability of the large cannon sprinklers depends on the stress distribution that occurs on the drive spoon caused by the impact force of the driving water jet. A simple theory of the forces caused by the impact of the water jet on the drive spoon was developed, and a three-dimensional (3D) model numerical simulation using computational fluid dynamics (CFD) was constructed. An experiment was carried out to verify the accuracy of the simple momentum-based theory and the numerical CFD simulations. The results showed a large deviation between the simulated and measured values under low pressure conditions, with a maximum deviation of 15.98%. However, the simulations had good accuracy under high pressure conditions. The difference between simple theory and experimental values also decreased with increasing working pressure when considering both horizontal and vertical components. The simple theory was adjusted by the use of correction factors that were regressed with working pressure using experimental data. The coefficient of determination of the correction factor expressions for both the horizontal and vertical components were 0.9799 and 0.9289 respectively. After adjustment of the simple theory, the calculated values of the vertical and horizontal impact forces were compared to the experimental values and had a difference <5%.