Fan Blade Tip Aerodynamics With Realistic Operational Casing Geometries and Clearances Available to Purchase

During engine operation fan casing abradable liners are worn by the blade tip, resulting in the formation of trenches. This paper investigates the influence of these trenches on the fan blade tip aerodynamics. A detailed understanding of the tip flow features for the fan blade under investigation is developed. A parametric model is then used to model trenches in the casing above the blade tip. It is shown that increasing clearance via a trench reduces performance by less than increasing clearance through cropping the blade tip. A response surface method is then used to generate a model that can predict fan efficiency for a given set of clearance and trench parameters. It is shown that the efficiency sensitivity to clearance is greater for cropped tips than trenches, and is biased towards the leading edge for cropped tips, and the trailing edge for trenches.