INFLUENCE OF NOZZLE ROUGHNESS ON CONDITIONS IN A GAS-BLAST EROSION RIG

Although the gas-blast method of erosion testing is widely used, little is known about the distribution of particle velocities and trajectories in the plume of erodent particles leaving the nozzle. In this work, experimental methods have been developed to study and describe these, and in particular the influence of the internal roughness of the nozzle has been examined. An analytical function has been derived which describes the angular distribution of particle trajectories in the plume; this distribution is uniquely described by a single dimensionless ''focus coefficient'', beta, which depends, among other factors, on the nozzle bore roughness and on the nature of the erodent particles. The nozzle roughness also significantly affects the velocity of the erodent particles; a rough nozzle bore is associated with lower erodent velocity, a greater spread of velocities and a more widely spread plume. The results are relevant to erosion testing by the gas-blast method, and suggestions are made for improvements in the control and standardization of the erosion conditions in such tests.