Numerical Simulation of the Axial Fan Performance Degradation Due to Sand Ingestion

This paper presents a method based on Lieblein and Koch correlations for assessing the performance degradation of an axial fan due to sand ingestion. The method is based on mean line analysis, and predicted aerodynamic performance includes the adiabatic efficiency, pressure rise coefficient and stall margin. Changes to the blade geometry which affect the fan aerodynamic performance are mainly due to erosion which reduces the blade chord and increases the tip clearance and surface roughness. Erosion damage has a significant effect on the aerodynamic lift coefficient, which is related to the static pressure distribution. An in-house developed trajectory code, combined with restitution factors and an erosion model (applicable for cast aluminium alloy and stainless steel), was used to predict particle trajectories and the amount of material removed. The method was applied successfully to a contra-whirl axial fan where reasonably good agreement was found between predicted and experimental results. Tests were conducted with MIL-E 5007E sand particle sizes of between 0.0 and 1000.0 microns. A method for predicting life expectancy of the fan is also presented. The methodology shows that critical blade parameters necessary for performance degradation simulation can be successfully obtained in this way.