When a gas turbine engine is shut down it will develop a circumferential thermal gradient vertically across the compressor due to hot air rising from the cooling metal components and pooling at the top. As the hot compressor rotor drum and casing cool and contract in the presence of this thermal gradient, they do so non-uniformly and therefore will bend slightly, in a phenomenon known as rotor bow. Starting an engine under bowed conditions can result in damage, representing a risk to both airworthiness and operational capability. This study consolidates some preliminary findings by the authors relating to the drivers for rotor bow, such as engine geometry, aircraft-engine integration and rotor temperature on shutdown. The commercial and military operational considerations associated with rotor bow are also discussed, including limitations which may result from a bowed rotor; the influence of operations including the final flight and descent profiles, taxi procedures and rapid turnaround requirements; as well as some practical solutions which may be implemented to reduce the impact of rotor bow.
