Impact characteristics of simulated hailstones during ingestion by turbofan aero-engines

Recent in-flight instances of aircraft engine power loss involving hail ingestion have forced the manufacturers to demonstrate successful engine operation whilst ingesting hail. The main objective of this research project has been to obtain an understanding of the basic characteristics of hailstone impacts. A hail gun was designed to fire simulated hailstones at speeds up to 175 m/s. Three measurement techniques were used to determine the impact characteristics of the hailstones, i.e: patternator, high speed cine-photography, and still photography with short duration flashes. Using these techniques, the basic impact characteristics in terms of post-impact particle size, velocity and mass distribution were obtained for a variety of target configurations. The influence of seemingly important parameters on the impact characteristics were investigated, including approach angle and velocity, target curvature, and target rotation. Studies were further made into multiple impacts, and the effect of target curvature and rotation on the impact characteristics. Based on the experimental results, a set of empirical rules and a mathematical model describing hailstone break-up were defined.